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EXAMS > Sensors > Flashcards

Sensors Flashcards

Sensors

1
Q

What is a wave?

A

Field disturbances that transfer energy from one location to another

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2
Q

What is a detector?

A

devices used to measure the characteristics of field disturbances

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3
Q

What do characteristics of disturbances reveal?

A

information about a waves origin

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4
Q

What can waves carry?

A

information from one location to another which is accessed by detection

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5
Q

What can EM radiation tell us about stars?

A

material composition

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6
Q

define passive sensing system

A

a system that generates a signal in response to a stimulus under normal environmental conditions

eg retina, some metal detectors

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7
Q

Define an active detection system

A

a system where the sensor requires a non natural stimuli to generate a signal, eg x ray system, MRI

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8
Q

Describe active detection in a cyber context

A

the sensor(s) uses a digital probe signal to instigate a response from a target, which is then measured. Requires more computing power and potentially less susceptible to data poisoning.

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9
Q

Describe passive detection in a cyber context

A

the sensor(s) measure ambient digital signals only, without the use of a probe on the target. Can be more susceptible to data poisoning than active measures

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10
Q

Describe binary classifiers

A

most detection cases we care about binary classification eg on/off, high/low, moving/stationary in a security context - threat/non threat

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11
Q

Describe a confusion matrix

A

red/green matrix, at simplest a 4 square grid
X axis - signal/actual/object
Y axis - detector response/predicted values
Green is real positives/negatives
Red is false positives/negatives

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12
Q

What is the X axis of a confusion matrix?

A

X axis - signal/actual/object

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13
Q

What is the Y axis of a confusion matrix?

A

Y axis - detector response/predicted values

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14
Q

What are the green regions of a confusion matrix?

A

Green is real positives/negatives

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15
Q

What are the red regions of a confusion matrix?

A

Red is false positives/negatives

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16
Q

On a 4 square confusion matrix, what are the 4 binary classifiers?

A

True positive - TP
True negative - TN
False positive - FP
False negative - FN

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17
Q

What are the 5 base calculations on a confusion matrix that help define how good a detector is?

A

Total positive = TP + FN
Total negative = FP + TN
Total true readings = TP + TN
Total false readings = FP + FN
Total readings = TP + TN + FP + FN

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18
Q

how to calculate accuracy on a confusion matrix

A

Accuracy = total positive / total measurements

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19
Q

What is specificity of a detector?

A

Specificity is the true positive rate

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20
Q

How do you calculate specificity?

A

True positive rate = TP / (TP + FN)

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21
Q

What is sensitivity of a detector?

A

true negative rate

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22
Q

how do you calculate sensitivity?

A

true negative rate = TN / (FP + TN)

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23
Q

What measure indicates that a detector will alarms correctly?

A

Specificity or true positive rate

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24
Q

What gives the probability that a detector will alarm incorrectly?

A

Incorrect alarm rate = 1 - true negative rate

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25
Q

Define a ROC curve?

A

Receiver Operator Characteristic curve is a way of plotting all possible confusion matrices to make it easy to identify the best threshold to make a decision.

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26
Q

define the axis of a ROC graph

A

X - False positive rate (1 - sensitivity )
Y - true positive rate (specificity )

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27
Q

What is 1, 1 on an ROC curve?

A

no true or false negatives

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28
Q

What does going up the Y axis on the ROC curve mean?

A

increased probability of detection

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29
Q

What does going up the x axis mean?

A

increase in the probability of false alarm

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30
Q

What is AUC?

A

Area under the curve

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31
Q

What is ROC sensitivity index?

A

d’ or D prime is the distance a ROC curve is from the 0,0 1,1 graph. in general, the further from the 0,0 1,1 graph the better the sensor is, but this will be dependant on risk appetite for false alarms.

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32
Q

4 particulate sampling techniques

A

Filters
impactors
dry cyclones
wetted wall cyclones

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33
Q

3 gas sampling techniques

A

Absorption
Adsorption
Condensation

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34
Q

4 key air sampling questions

A

Why are you sampling
what are you sampling
where are you sampling
how long are you sampling for

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35
Q

7 main analytes

A

aural
biochem
magnetic
optical
radiological
thermal

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36
Q

define an analyte

A

a substance who’s chemical constituents are being identified and measured

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37
Q

what is the prerequisite for detection of a stimulus?

A

must be present in sufficient CONCENTRATION or INTENSITY so it can be DETECTED and DIFFERENTIATED from the environment

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38
Q

4 routes of entry to the human body

A

respiratory
percutaneous
ocular
ingestions

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39
Q

2 features of the air we breathe

A

Highly diverse
Ambient aerosol

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40
Q

Define highly diverse

A

already contains bacteria, viruses and toxins

infections are from an aerosol route

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41
Q

Define ambient aeresol

A

contains naturally occurring aerosolised particles physically identical to threat particles present at continually fluctuating levels

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42
Q

6 particulate sampling techniques

A

filtration
impingement/impaction
sedimentation
precipitation
thermal
electrostatic

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43
Q

4 stages of air sampling

A

pre-separator
filter/collection
media airflow
controller pump

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44
Q

Features of PM10 high volume air sampler

A

Flow rate between 1-1.7 m^3/min

size selective inlet allow for particles of pre determined range to be captured on a quartz filter (usually less than 10 microns and filter paper determines the minimum size)

filter weighted before and after use to determine the mass of particulates caught

controlled by mass flow controller or volumetric flow controller

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45
Q

types of filter (8)

A

glass fibre
quartz fibre
borosilicate
fibrecellulose and mixed cellulose esters (MCE)
PTFE PM 2.5
Glass fibre tape
Andersen impactor filters
Polycarbonate filter

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46
Q

Concentration calculation

A

concentration = mass of pollutant / volume of air

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47
Q

gravimetric concentration formula

A

SP = (Wf-Wi)/V(T) x 10^6SP = mass concentration of suspended particulate
Wf = final weight of filter
Wi = initial volume of filter
V(T) = total volume of air sampled
10^6 = conversion of g to ug

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48
Q

Define aerodynamic diameter of a particle

A

a sphere, whose density is 1 g cm^-3 which settles in still air at the same velocity as the particle in question

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49
Q

Define Mass Median Aerodynamic Diameter

A

is defined as the diameter at which 50% of the particles by mass are larger and 50% are smaller.

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50
Q

Define Geometric Standard Deviation (GSD)

A

is a measure of the spread of an aerodynamic particlesize distribution. Typically calculated as follows:GSD = (d84 /d16)^1/2where d84 and d16 represent the diameters at which 84% and 16% of the aerosol mass are contained, respectively, in diameters less than these diameters.

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51
Q

Types of air sampler (*)

A

Cyclone3 piece cassette
swirling aerosol collector
AGI 30
Slit sampler
Andersen sampler

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52
Q

3 categories of materials for sensing

A

Structural, functional, biomaterials

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53
Q

Define structural material

A

Structural materials are used for their structural integrity and mechanical behaviour. Strength, weight, toughness, hardness…

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54
Q

Define functional material

A

Functional materials are used for their function or response to a stimulus e.g. magnetic , electrical, optical

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55
Q

Define biomaterials

A

materials that have been designed to interface with biological systems, for the treatment, augmentation, or replacement of biological functions. Biomaterials and biological systems interact both ways.

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56
Q

% categories of materials

A

metal, ceramic, polymer, glass, composite

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57
Q

Triangle of material choice

A

processing Properties Structure

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58
Q

Define processing of materials

A

the journey from the ground to a usable material in a system ore - purify

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59
Q

What is the difference between detect to treat and detect to warn?

A

Detect to warn systems must respond in sufficient time to allow protective measures to prevent or minimize exposure of a significant portion of the at risk population.
Detect to treat is much longer as you accept people will be affected, you look to mitigating the severity of the exposure

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60
Q

What is detect to treat?

A

Detect to treat is much longer as you accept people will be affected, you look to mitigating the severity of the exposure

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61
Q

what is detect to warn?

A

Detect to warn systems must respond in sufficient time to allow protective measures to prevent or minimize exposure of a significant portion of the at risk population.

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62
Q

Detection strategy for detect to treat

A

Point sensing

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63
Q

Detection strategy for detect to warn

A

Stand-off sensing Eg LiDAR

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64
Q

What do we mean by generic detection?

A

detection of a range of threats ie wide groups of bacteria which a small group might be a threat agent

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65
Q

What analytical systems provide generic detection

A

LIDAR

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66
Q

what is flow cytometer?

A

pass a cell suspension through a light source and measure the fluorescence from the agents

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67
Q

What do we mean by structural sensing?

A

detection of a threat by use of the structural elements of the threat, usually from binding to part of these elements with something that is easy to detect e.g. an agglutination test

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68
Q

What are the five bio-analysis methods?

A

Culture
Microscopy
Immunoassay
PCR
Chemical Assays

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69
Q

Describe Method of Bioanalysis Culture

A

grow agents in conditions that specifically relate certain types of bacteria/fungi etc ie rose Bengal agar is a growing media that inhibits bacteria and allows the identification of the presence of yeast and moulds

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70
Q

Describe Method of Bioanalysis Microscopy

A

Morphological identification of particles

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71
Q

Describe Method of Bioanalysis Immunoassay

A

particles with specific epitopes matching the assay antibodiesparticles with parts of the allergen that are identified by the body (epitodes) that in this case match the antibodies present in the assay test.

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72
Q

Describe Method of Bioanalysis PCR

A

DNA matching test

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73
Q

Describe Method of Bioanalysis chemical assays

A

identify the biomass of specific chemicals eg ATP

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74
Q

Limitations of bioanalysis method culture

A

underestimates concentration of all organisms
nonculturable organisms are invisible
non culturable are classed as noninfective

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75
Q

Limitations of bioanalysis method microscopy

A

limited to groups of organisms, not specific strains

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76
Q

Limitations of bioanalysis method immunoassay

A

limited to organisms that the assay is designed for, therefore only binary resultsCross reactivity is common

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77
Q

Limitations of bioanalysis method PCR

A

limited to organisms that the assay is designed for, therefore only binary results
highly specific
highly sensitive

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78
Q

Limitations of bioanalysis method Chemical analysis

A

only an indicator for large quantities of organisms

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79
Q

what is meant by direct binding event?

A

direct binding of the target to a specific molecular recognition element

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80
Q

how does direct binding event works?

A

a reversable ‘lock and key’ event like an antibody with a viral protein

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81
Q

9 molecular recognition elements for biosensing

A

single strand DNA
Antibody
Peptide
Enzyme
Lectine
Receptor
Aptamer
Small molecule
Imprinted molecule

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82
Q

What is an antibody?

A

also known as an immunoglobulin Ig is a large, Y shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses.

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83
Q

How do immunoassay ticket systems work?

A

liquid sample added to test strip and other reagents added if required

target molecules wick through the ticket, bind to immobilized agents and detection molecules in a ‘sandwich’ format

wick usually travels through a testing area before reaching a control line, if no line shows up on control after allotted time, then the test needs repeating.

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84
Q

Define SELEX?

A

Systematic Evolution of Ligands by EXponential Enrichment

a method of increasing the number of DNA/RNA strands required for testing and use them to sequence and characterise DNA found in the environment

The starting single stranded DNA or RNA library(10 14 ~10 16 random oligonucleotides) is composed of sequences 20~100 nucleotides in length with a random region in the middle flanked by fixed primer sequences.

After incubation with the target of interest, the bound

oligonucleotides are partitioned from unbound sequences and amplified by PCR .

repeated 2-15 times before used as biomarker identification tools.The resulting enriched DNA pool is used for the next round of selection.

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85
Q

What is SELEX short for?

A

Systematic Evolution of Ligands by EXponential Enrichment

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86
Q

6 high level approaches for structural sensing

A

Magnetic
optical
electrochemical
mass
acoustic/piezoelectric
MEMS

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87
Q

Types of optical

A

Fluorescence
Absorbance
SPR/RM
Luminescence
RAMAN

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88
Q

Types of magnetic

A

magneto-elastic
giant magneto-resistance (GMR)

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89
Q

types of MEMS (*)

A

MEOMScantileversmicrofluidsmicrocalorimetry

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90
Q

types of acoustic/piezo-electric

A

surface wave acousticquartz microbalance

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91
Q

types of mass

A

time of flight
ion trap
ion mobility (MS/MS)

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92
Q

types of electrochemical

A

amperometry
potentiometric
conductimetric
molecular electronics

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93
Q

What is a molecular recognition element?

A

Molecular recognition event is typically a specific interaction that is reversible, analogous to the interaction between a lock and a key, although in many cases the binding would more accurately be described as induced fit, during which the recognition element changes shape upon binding.

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94
Q

What does a direct binding event rely on?

A

Affinity of the target for the molecular recognition elements

Non-specific binding of extraneous material at the binding site

Sensitivity of detection

If attomolar (10 18 ) detection levels are required then high affinity molecular recognition elements with minimal non specific binding required

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95
Q

considerations for structure based sensing?

A

Sample collection,

Sample concentration,

Binding of the target to the molecular recognition element,

Possible addition and removal of “reporter” groups,

Detection of target molecular recognition element complex,

Analysis of the output signal,

Renewal of the sensor surface for repeated monitoring.

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96
Q

target inhibitor for single strand DNA?

A

complementary sequence of DNA

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97
Q

target inhibitor for Antibody

A

proteins, carbohydrates, small organic molecules etc

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98
Q

target inhibitor for Peptide

A

proteins, carbohydrates, small organic molecules etc

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99
Q

target inhibitor for enzyme

A

substrate such as biochemicals like glucose, acetic acid

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100
Q

target inhibitor for lectin

A

carbohydrate

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101
Q

target inhibitor for receptor

A

proteins, carbohydrates, small organic molecules

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102
Q

target inhibitor for aptamer

A

proteins, carbohydrates, small organic molecules etc

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103
Q

target inhibitor for small molecules

A

proteins, cells etc

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104
Q

target inhibitor for imprinted moelcules

A

proteins, small organics molecules, whole cells etc

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105
Q

8 SELEX methods

A

IP-SELEX
Capture-SELEX
Cell-SELEX
CE-SELEX
M-SELEX
AFM-SELEX
AEGIS-SELEX
Animal-SELEX

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106
Q

Key aspects of IP-SELEX

A

includes immunoprecipitation

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107
Q

Key aspects of Capture-SELEX

A

oligonucleotide library is immobilized on a support instead of the targets to identify aptamers against small soluble molecules

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108
Q

Key aspects of Call-SELEX

A

utilizes whole live cells as targets for selection of aptamers

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109
Q

Key aspects of CE-SELEX

A

involes separation of ions based on electrophoretic mobility

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110
Q

Key aspects of M-SELEX

A

combines SELEX with a microfluid system

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111
Q

Key aspects of AFM-SELEX

A

employs AFM to create a 3D image of the sample surface

112
Q

Key aspects of AEGIS-SELEX

A

utilizes libraries with the artificially expanded genetic code

113
Q

Key aspects of animal-SELEX

A

aptamers are selected directly within live animal models

114
Q

advantages of IP-SELEX

A

selects aptamers against proteins under normal physiological conditionsincreased affinity and specificity

115
Q

advantages of Capture-SELEX

A

suitable for the selection of aptamers against small moleculesimmobilization of the target not requiredused for discovery of structure switching aptamers

116
Q

advantages of Cell-SELEX

A

Prior knowledge of the target not requiredAptamers are selected against molecules in their native stateMany potential targets available on the cell surfaceProtein purification not required

117
Q

advantages of CE-SELEX

A

Fastonly 1-4 rounds of selection requiredreduced non specific bindingtarget immobilization not required

118
Q

advantages of M-SELEX

A

RapidVery effective (small amounts of reagents required)Applicable to small moleculesAutomatable

119
Q

advantages of AFM-SELEX

A

able to isolate high affinity aptamersFast 3-4 rounds

120
Q

advantages of AEGIS-SELEX

A

high specificity of the selected aptamers

121
Q

advantages of animal-SELEX

A

selected aptamers bind the targets in their natural environmentPrior knowledge of target not requiredMinimal optimization needed

122
Q

disadvantages of IP-SELEX

A

more time consuming than standard SELEX

123
Q

disadvantages of Capture-SELEX

A

some oligonucleotides from the library might not be released/selected

124
Q

disadvantages of Cell-SELEX

A

suitable for cell surface targetsRequires high level of technical expertiseCostlyTime consumingPost SELEX identification of target required

125
Q

disadvantages of CE-SELEX

A

not suitable for small targetsexpensive equipment

126
Q

disadvantages of M-SELEX

A

Not suitable low purity/recovery of aptamerstarget immobilization required

127
Q

disadvantages of AFM-SELEX

A

expensive equipment requiredImmobilization of target aptamers required

128
Q

disadvantages of AEGIS-SELEX

A

Poor recognition of the unnatural bases by natural DNA polymerases

129
Q

disadvantages of Animal-SELEX

A

time consuming (man rounds required)

130
Q

Dog’s nose; how does this compare with current detection systems?

A

test kits in the range of 1g-1ug (visible to particles)Field instruments in the range of 1ug-1pg (particles/vapour)Dogs in the range of 1fg-1ag (vapour)

131
Q

Dog density of olfactory epithelium?

A

170cm^2(humans have 10cm^2)

132
Q

How does the dog receptors mean it has a better sense of smell?

A

It is the interactions of odour molecules with specific receptor proteins that give specificity.

Each olfactory odour receptor neuron has only one functional odour receptor; if the odour molecule interacts with the receptor then the nerve cell will respond.

133
Q

Define nuclear forensics

A

the use of scientific techniques to investigate potentially criminal uses of radiological and/or nuclear material. most commonly used for counter proliferation purposes, but does have growing use in health and safety outside of civil nuclear too.

134
Q

3 goals of nuclear security policies

A

–Development and control of military applications of nuclear energy

Finding ways to curb the proliferation of states, or even non state actors, with nuclear capabilities; failing that

Receiving best possible information on the nuclear programme or weapon arsenal of other states.

a growing fourth area - reduce the use of RN material as a non monetary criminal currency

135
Q

4 linkages that nuclear forensics can provide

A

people
places
materials
events (including time components)

136
Q

IAEA definition of nuclear forensics

A

Nuclear forensics is the examination of nuclear or other radioactive materials, or of evidence contaminated with radionuclides, in the context of legal proceedings under international or national law related to nuclear security

137
Q

Types of radiation for detection

A

Alpha
Beta
Gamma
Neutron
Muon - not radioactive but part of high energy physics which most RN physicists are best placed to study this as well

138
Q

Detection for alpha/beta

A

scintillator
Signal analyser

139
Q

types of detector for gamma

A

Gamma spectrometers consist of a (usually HPGe )detector used for measuring photon energies, apre amplifier, an amplifier, an analogue to digitalconverter (ADC ) and a multichannel analyser(MCA).

140
Q

types of detector for neutron

A

He-3 gas with photomultiplier giving a count per unit time response

141
Q

what is a neutron particle?

A

3 quarks, 1 up and 2 down which are generated in some nuclear decay chains and neutral in charge so very difficult to detect.

present in the decay chains of plutonium and uranium which could indicate the presence of special nuclear material. this is useful for standoff detection.

142
Q

what is and alpha particle?

A

a helium atom without the electrons, low travel distance and low penetration properties (sheet of paper will stop them)

143
Q

what is an neutron particle?

A

3 quarks, 1 up and 2 down which are generated in some nuclear decay chains, most usefully the decay chains of plutonium and uranium which could indicate the presence of special nuclear material. this is useful for standoff detection.

144
Q

what does a scintillator do?

A

converts energy lost by ionising radiation into pulses of light in solids or liquids which then interacts with a photocathode to give an electron multiplied in a Photo Multiplier Tube (PMT) to give electrical signal

145
Q

What does the signal do?

A

analysed by a multi channel analyser and the intensity of each alpha particle energy is taken. it is the intensity at each energy level that allows an analyst to work out what types of radioactive material is present. noting there will probably be multiple elements in differing quantities so the decay chain is useful to cross reference with.

146
Q

materials for scintillators

A

organic (plastic) or inorganic (ZnS or NaI)

147
Q

how do you limit thermal noise?

A

electron hole production creates noise which can be mitigated by cooling in liquid nitrogen.

148
Q

What are the axis of a gamma spectrum graph?

A

y axis - counts
x axis - particle energy

149
Q

What happens to the signal in a gamma spectrometer?

A

The preamplifier converts a charge pulse to avoltage pulse, while the amplifier provides avoltage gain .

The ADC transforms the signal to adigital pulse that is used as input to the MCA.

The MCA sorts the pulses according to their pulse height , which is proportional to the photoninteraction energy.

150
Q

AWE objective for nuclear forensics

A

Develop and provide end to end operational response capabilities for detection, recovery, analysis, characterisation and technical attribution from all scenarios, exploiting nuclear and conventional forensics capabilities.

151
Q

what does nuclear forensics + conventional forensics =

A

total forensic exploitation

152
Q

Define nuclear characterisation

A

is the determination of a sample’s characteristics. It typically involves an elemental analysis of the sample, most often including isotopic analysis of nuclear materials (i.e. U and Pu) and selected minor constituents (e.g. Pb ). It also includes physical characterization e.g. measuring the key dimensions of solid samples, or for powders particle size and shape distribution.

153
Q

Define nuclear reconstruction

A

is the process of combining the information from interpretation with all other available information (e.g. from forensic analysis of non nuclear evidence associated with the sample or from intelligence sources) to determine as full a history as possible of the RN material. This phase is called attribution in the contexts of investigations of nuclear trafficking and terrorism events.

154
Q

what are the skills AWE have that make them import to the UK in nuclear security?

A

Hazardous materials of concern are used as part of AWE’s other core MOD programmes in support of the UK’s nuclear deterrent over the last 60 years.

Unique knowledge base in AWE’s personnel and AWE’s facilities for characterisation of explosives, bulk SNM, radioactive materials.

AWE provides key RN technical support to the UK CBRNE Operational Response

155
Q

RN types of signature that can be assessed (*)

A

Shape
Measurement
markinggrain analysismicroscopychemical characteristics - composition of the uranium
rare earth elemental pattern of the ore
major, minor and trace constituents

156
Q

describe point sensing

A

this is the processes of taking a sample of an analyte and putting it through a sensing capability

157
Q

describe standoff sensing

A

the process of trying to identify a potential threat from a long way away

158
Q

differences between point and standoff sensing

A

In point detection applications, the biological organisms must pass through the actual detection element.

Standoff detection is detection of a biological agent cloud at some distance on the order of kilometres from the target and from the detector

159
Q

What is LIDAR?

A

LIght, Detection And Ranging
essentially a light illuminated radar system

160
Q

uses of LIDAR in chem bio sensing

A

using a UV 297nm laser biological agents can be induced to fluoresce which can then be detected

161
Q

other uses of LIDAR

A

navigation and positioning
obstacle detection
plant regrowth
wind speed,
turbulence etc (with doppler systems)
speed guns
3d scanning

162
Q

Define DIAL

A

Differential absorption lidar

Allows for detection of aerosols and gases in atmosphere

163
Q

Differences between LIDAR and DIAL

A

DIAL uses 2 lasers sources, one of the absorption band of interest, the other slightly outside this band and the difference in the intensities allow a concentration of molecule of interest to be calculatedLIDAR is single source and usually based on time of flight

164
Q

Define LIBS

A

laser induced breakdown spectroscopy

high power laser beam generates a plasma plume, the cooling plasma allowing elemental emission lines to be observed

Very good for explosive identification

165
Q

Point detection systems

A

DNA analysis
PCR
Gas chromatography
Mass Spectrometry

166
Q

Point sensing cons

A

ones based on aerosol particle counting with size generate unacceptable false positives

unable to distinguish attack vs normal fluctuations in 1-10um range

167
Q

Point sensing pros

A

size and shape analysis combined with UV-LIF is rapid and best used in a building environment due to controllable background noiseoxidation of organisms determined by NAD(P)H fluorescence is a potentially exploitable signature for near real time detection

168
Q

Standoff detection cons

A

Long range IR LIDAR cannot distinguish between bio and non bio particles, so high false positive rate

Operational systems need to employ temporal comparisons of spectral signatures to decrease false positive readings due to fluctuations in background signatures.

169
Q

Standoff pros

A

Short range use of UV LIF provides near real time discrimination of biological from non biological particles.

The ability to use shorter excitation wavelengths for short distances where atmospheric propagation is not an issue allows information containing spectral properties to be gathered from aerosolized particles

170
Q

2 types of LIDAR (*)

A

direct energy detection (or incoherrent)coherent detection

171
Q

steps in a LIDAR chain

A

laser transmitter
scatter from targets
recieving optics
optical filter
photodetector
data acquisition

172
Q

Define Nyquist-Shannon sampling theorem

A

“If we sample a signal at twice its highest frequency, then we can recover it exactly.” However, if the signal is sparse fewer samples are needed for reconstruction

173
Q

Define Compressed sensing (CS) (or sparse sampling)

A

a novel paradigm in data acquisition that allows representing sparse data in an efficient and accurate way, using sparse recovery (SR) techniques based on nonlinear interpolation

174
Q

What is the key idea of compressed sensing?

A

to recover a sparse signal from very few nonadaptive, linear measurements by convex optimization

175
Q

Examples use of compressed sensing

A

Computed tomography
image reconstruction

176
Q

Steps in compressed sensing

A
  1. Measure projections
  2. First image estimate
  3. simulated projections / corrected projections
  4. comparison
  5. correct images
  6. iterative cycle - 3, 4, 5
  7. end point - final images
177
Q

What is machine learning?

A

study of computer algorithms that improve automatically through experience

178
Q

What tasks are suitable for machine learning? (x3)

A

spam filtering
pattern recognition
data mining

179
Q

conventional engineering design flow

A

acquisition of domain knowledge(physics based mathematical model)

Algorithm development (algorithm with performance guarantees)

180
Q

machine learning design flow

A

acquisition of data(training set)
hypothesis class > learning(black box machine)

181
Q

3 types of machine learning

A

supervised learning
unsupervised learning (clustering)
reinforcements learning

182
Q

What is required for supervised learning?

A

input and output data are known

183
Q

What is required for unsupervised learning?

A

input only is known

184
Q

What is required for reinforcement learning?

A

input data and quality measure is known

185
Q

what is an x-ray

A

high energy EM radiation
essentially the same as gamma radiation
Do not interact with matter much
find it hard to pass through dense materials

186
Q

formula for photon energy

A

plancks equation
E = hv
E= energy
h = placks constant 6.626x10-34 J.s
V = frequency in Hz

187
Q

wavelength of x-rays

A

0.01-10nm
hard x-rays are wavelengths under 0.2-0.1 nm

188
Q

energy of hard x-rays

A

have energies above 5-10 KeV

189
Q

4 parts of an Xray system

A

source
target
detector
signal processing/detection algorithm

190
Q

components of an X ray source

A

hot cathoderotating anode (around 10,000 rpm, heat generated approx. 2000C)
tungsten target angled 12-15 degrees (though molybdenum or graphite can be used)
Rotator

191
Q

generation of xrays - how are K lines generated?

A

by high velocity electron from the anode knocking out an electron from the K (S) orbital and outer shell electrons dropping to lower energy states and releasing energy in the form of x rays as they do so.

192
Q

generation of xrays - what are the characteristic interaction alpha and beta peaks created from?

A

alpha from 2p (outer L) shell to 1s (K) (smaller peak)

beta from 3p (middle M) shell to 1s (K) (higher peak)

193
Q

generation of xrays - what is bremsstrahlung radiation?

A

where a high energy electron passes close to a nucleus, it does not interact with the electrons, but is deflected by the nucleus, this deflection slows the electron and bremsstrahlung radiation is emitted with energy being proportional to how close to the necleus it was (the closer the higher the energy)

194
Q

2 types of x ray detector/sensor

A

Scintillator

direct converstion

195
Q

define scintillator

A

these operate by converting packets of xray radiation into wavelengths which can then just be detected using CMOS/CCD devices that produce and electrical signals

196
Q

define direct conversion (x-rays)

A

x-ray photons are directly converted to electrical signals

197
Q

Pros of direct conversion over scintillator

A

better energy resolution
better spatial resolution
higher signal conversion efficiencies

198
Q

steps of scintillator detection

A

Xray scintillator (xray converted to light, causes scattering)
photodiodeelectric circuit (TFT or CMOS)
image

199
Q

steps of direct detection

A

xrayCdTe (xray converted to electrical signal, minimal scattering)
CMOS circuit
Image

200
Q

Define CT scan

A

Computer tomography table moves through source/detectors and they move around target taking slices over time which are then used at the signal processing stage to build a 3d image

201
Q

Pros and cons of CT

A

pro
3d so can lead to better object identification
can hold certain scans on file for checking for addition/subtraction of material
comprehensive

con
higher dose rates, so may be unsuitable for circumstances where people might be exposed eg lorry backstakes a lot longer

202
Q

Define function based sensing

A

A function based detector is defined as a naturally occurring biological organism or portion of that organism (whether organ, tissue, cell, or receptor) that reacts in a measurable way when exposed to a range of chemical or biological toxic material. eg canary in coal mine

203
Q

differences between structure and function based sensing

A

Structure sensing is based in finding the agent that causes the problem
Function based sensing is looking for evidence that the agent is present eg contrails/emissions to find planes

204
Q

Describe a cell based system (x2)

A

inherent system where natural processes are exploited for detection

Engineered system, where a cell has been genetically engineered or had sensing materials added to them

205
Q

what is a hybrid system?

A

Hybrid systems exploit part of the functional process within a cell based response system, even as they are targeted at a specific characterized function.

206
Q

Describe an enzyme based chem detection system

A

NAIAD - nerve agent detection system
The bioreceptor in this case is the enzymebutyrylcholinesterase , which exhibits the same enzyme activity as human acetylcholinesterase.

The enzyme is immobilized onto a temperaturecontrolled pad that is continually washed with butyrylthiocholine methane sulfonate in an aqueousphosphate buffer.

The enzyme catalyses the hydrolysis of the ester, producing butrylthiocholine , and the concentration is monitored by an electrochemical cell arrangement(this is the transduction system).

If nerve agent is present, it inhibits the butyrylcholinesterase , which in turn causes an alteration in the electrical potential within the electrochemical cell, thus triggering an alarm at a present level.This type of detector is extremely sensitive to low levels of nerve agents such as tabun and sarin. Also HCN.

207
Q

Describe an ion based sensing system

A

, Competitive assay. Here a similar membrane is formed except that it contains hapten linked gramicidin, ( G h ). The membrane is rinsed with a streptavidin solution after which an appropriatebiotinylated, hapten specific Fab′ is added, forming complexes between the MSL α and the G h . The G h is thus tethered distant from its immobilized inner layer partners, G T , preventing the formation of dimers and lowering the electrical conductance of the membrane. The sensor is stored in this state until the addition of analyte competes with the hapten for the Fab′, liberating the channel and resulting in an increase in the membrane conductance

208
Q

How can chromoatophores be used in sensing?

A

Fish chromatophores from Betta splendens are used as the cytosensor element in the development of a portable microscale device capable of detecting certain environmental toxins and bacterial pathogens by monitoring changes in pigment granule distribution.

Cell based biosensor prototype. The chamber containing chromatophores has wicks inserted for sample delivery,and is placed into the holder. An agent can be applied to the top wick, and the response of the chromatophores is imaged using the LED light source, lens and camera. The image is then processed by the statistical program present in the computer.A heterogeneous population of chromatophores is always present in primary tissue culture, and not all cells respond equally when exposed to many of the environmental toxins tested.

209
Q

define a chromatophore

A

Chromatophores, which are pigment cells responsible for the brilliant colours of fish, amphibians, and reptiles.

210
Q

considerations of function based systems (7)

A
  1. slow (minutes to hours) response time
  2. mostly lab based rather than field deployable
  3. Cell based assays prone to poisoning by environmental pollutants
  4. Prone to false alarms if not carefully characterised for selectivity, specificity and sensitivity
  5. Process of sampling air and getting sample to the cell needs attention
  6. preparation of sample adds time to the overall response time
  7. needs a life support system is still living
211
Q

Examples of function based sensing

A

Canaries in coal mines, sarin
Chickens as sentinels for encephalitis virus
Daphnia to indicate water quality
Poland, 8 regularly changes mussels are used to detect water quality changes

212
Q

limitations of function based sensing?

A

less specific
less selective
therefore potential for false positives is high
Do not measure concentrations
rely on transduction devices to measure response

213
Q

Strengths of functional detection

A

can detect presence of wide range of unknown chembio agents

214
Q

Describe an example hybrid system

A

PANTHER
PAthogen Notification for THreatening Environemtnal Releases

uses cellular analysis and notification of antigen risks and yields to detect pathogens including anthrax, plague, e.coli etc

215
Q

How does PANTHER work

A

use genetically engineered jellyfish cells to use antibodies to bind to threats. once a binding has occurred, Ca ++ are released. A bioluminescent protein from the jellyfish cells is released in response to the Ca++ increase, emitting light which is then detected.

216
Q

What do we mean by learning from nature in the context of detecting material of interest? (X5 topics)

A

chemical detection
infrared
electrical
magnetic
radiation

217
Q

Explain how studying nature can aid the development of situational awareness sensing systems?

A

radically different ways of design and manufacturing of components and systems

218
Q

What is the purpose of a conceptual model?

A

provides an overview of how different areas of learning from nature overlap

219
Q

Describe the 10 different types of sensing found in nature and how can they be used in a security context?

A

Chemical
Infra red
vibration
pressure
fluid flow
strain
magnetic
electric
fieldtouch
EM radiation

220
Q

What new functionality has been derived from nature?

A

– Specificity and sensitivity of sensors (e.g. snake (IR), moth (chemical))

– Navigation without maps & GPS (optic flow in insects, migrating birds)

– Optimised integration of sensors and processing

– Sustainability, adaptive capability (physically and behaviourally)

– Low processing energy demands; distributed energy.

221
Q

What Radically different way of designing and manufacturing components and systems have come from nature?

A

Exceptional packaging and integration

Self assembly and repair

Optimum low energy design (low temperature fabrication using readily available material, integration of functions, locomotion, tracking)

222
Q

6 topics in the bio design concept map

A

robotics
bionics
bioinspiration
biomimetics
biomimicry
eco-design

223
Q

5 areas of learning from nature

A

Bio mimicry
bio mimetics
bio derived materials
bio fabrication
bioinspired

224
Q

define bio mimicry

A

Study of nature, its models, systems, processes and elements and then imitates or takes creative inspiration from them to solve human problems.

225
Q

define bio mimetics

A

The underlying biological paradigms present keeping each species functioning in its own unique way.

226
Q

define bio derived materials

A

matierals made from or originating from living organisms

227
Q

define bio fabrication

A

A process using cells, viruses, proteins, biomaterials and bioactive compounds as building blocks to fabricate advanced biological models, medical therapeutics and non medical biological systems

228
Q

define bio inspired

A

Ideas inspired by mechanisms or laws operating in biological organisms. Or a conscious strategy by designers to observe and learn principles of design from nature.

229
Q

components of a situational awareness sensing system (SASS) (*)

A

structure
collection sampling
processing (communications)
surfaces / receptors
power
sensor element transduction

230
Q

4 components of structure for SASS

A

Function

Scale

Morphology

Materials

231
Q

5 components of surfaces with relation to SASS

A

surface area
surface modification
materials
connectivity
degradable/fouling

232
Q

3 collection and sample types

A

airwater solid

233
Q

4 components of receptors in relation to SASS

A

antibodies
bio probes
synthetic ligands
molecular

234
Q

3 components of processing and communications

A

internal

collective

external

235
Q

6 components of power

A

energy harvesting
fuel cells
photosynthesis/photoelectric
chemical
storage accumulators
power management

236
Q

Chart of processing information

A

Digital signal processing
compressive sensing
biology

237
Q

What are the 4 components of DSP

A

collect
compress
reconstruct
analyze/act

238
Q

3 components to CS

A

sparsely sample

reconstruct

analyse/act

239
Q

2 components to biology processing information

A

sparsely sample

analyse/act

240
Q

fiddler crab vision example

A

• Biological systems compressively sample environment and do not reconstruct to make critical decisions (Compressive Sensing)• This is achieved by having hard coded, neural circuitry that responds only to necessary information (Machine learning)social zone lower levelpredator zone upper level

241
Q

human vision example of CS/ML

A

colour vision only in the centre, peripheral vision only in black and white

242
Q

Nature - types of chemo sensing

A

olfaction
gustation (taste)
surface contact (touch)

243
Q

What is a ROC curve?

A

receiver operating characteristics curve shows either how different detectors respond compared to the same parameters, or how the same detector changes its detection ability in different environments when controlled for same detection confidence and fixed response time
closer to Y axis, the more real alarms are being seen closer to the x axis, the more false alarms present

244
Q

what is a detection assay?

A

a way of qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity

245
Q

Describe a sampling system

A

a system that autonomously or with human interaction through a series of agreed processes, can take a sample from an environment requiring testing, use one or more sensors to try to identify threats, then provide an response to an analyst.

246
Q

What the characteristics of a biosensor ? 14 points

A

specificity
sensitivity
speed
cost
reliability
ease of manufacturing
size
weight
power and consumables
ability to work in complex mixtures
low false positive rate
multianalyte detection
continuous/batch sensing
ease of operation
viability (live vs dead organisms)

247
Q

What is meant by the response time

A

time taken from a sensor reaching the limit of detection to generating an alarm

248
Q

What is LOD?

A

limit of detection or detection threshold - the minimum agent concentration required for a sensor to generate an alarm.

249
Q

why is LOD important?

A

because it is the key trigger point for a system to enter an alert state

250
Q

What is a spider chart used for?

A

demonstrating the results of 12 specifications of one or more sensors

251
Q

what is a spider chart?

A

12 spoked wheel where each spoke is a measurable requirement for the sensor system. usually the further from the centre the better the system

252
Q

12 specifications of a spider chart?

A

weight
power
consumption
Unit cost
reliability (MTBF)
Operating costs
MTBM
false positive rate (low dose rate)
false positive rate (high dose rate)
response time
detection confidence
sensitivity
size

253
Q

Explain deployment analysis?

A

assessment of 18 cardinal points to provide a final summary of how effective a system is, in ability to detect, but also maintain, continuously function and cost benefit

254
Q

units for weight

A

Kg though dependant on system in vivo could be mg, platform could be tonnes

255
Q

units for power consumption

A

watts

256
Q

unit for unit cost

A

£ or currency of country using device. that said, $ cost does help as an internationally understood baseline for most costings

257
Q

What is MTBF?

A

mean time between failures, or the average time between repairable failures of a technology product

258
Q

unit of MTBF

A

months, though could be context dependant to secs to years

259
Q

units for operating costs

A

£ per year

260
Q

What is MTBM

A

mean time between maintenance

261
Q

unit of MTBM

A

weeks, though could be system dependant

262
Q

unit of false positive rate

A

number per year, though could be context dependant, so covid with national screening policies could be rate per day

263
Q

response time unit

A

seconds

264
Q

unit of detection confidence

A

percentage calculated from confusion chart and ROC measurements

265
Q

unit for sensitivity

A

ACPLA - Agent Containing Particle per Litre of Air

266
Q

unit of size

A

m^3

267
Q

Is there such a thing as a one size fits all sensor?

A

no, and usually the opposite is true, should a sensor be described as a one size fits all, then it usually fails to meet the minimum requirements for any application.

268
Q

Define noise

A

is fluctuation in sensor responses due to factors that are independent of the measurement environment.

a signal to noise ration of more than 1 is important, though in some cases not necessary/ possible.

in these cases more processing like conducting a Fourier transform on the data is required, but this does affect the fidelity of the output.

269
Q

define clutter

A

is the sensor response to all factors associated with the measurement environment other than the agent.

270
Q

define signal

A

is the sensor’s response to the agent.

271
Q

18 cardinal points specifications for a bio sensor

A

specificity
selectivity
sensitivity
speed of response
stability
reproducability
repeatability
reliability
range
resolution
low false positive rate
multi analyte detection
continuous/batch sensing
ease of operation
viability
ease of manufacture
size ,weight ,power
cost

272
Q

5 S’s of cardinal points

A

specificity
selectivity
sensitivity
speed of response
stability

273
Q

4 R’s of cardinal points

A

Range
resolution
repeatability
reliability

274
Q

8 multi letters of cardinal points

A

low false positive rate
multi analyte detection
continuous/batch sensing
ease of operating
viability
ease of manufacturing
SWAP (size weight and power)
Cost

275
Q

Summary of cardinal points (13 points)

A

inital cost
operating cost
response time
limit of detection
power consumption
mission duration
consumables
maintenance
reliability
ruggedness/operationally hardened
form factor
environmental considerations

EXAMS (6 decks)

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