bluuebunny/crossref_metadata_2025 huggingface dataset:
A low-pressure cloud chamber to study the spatial distribution of ionizations
Authors: D C Hodges  , M Marshall
Published: July 2002

To further the understanding of the biological effects of radiation a knowledge of the spatial distribution of ionizations in small volumes is required. A cloud chamber capable of resolving the droplets formed on individual ions in the tracks of low-energy electrons has been constructed. It is made to high-vacuum specifications and contains a mixture of permanent gases and vapours, unsaturated before expansion, at a total pressure of 10 kPa. Condensation efficiencies close to 100% are obtained without significant background from condensation on uncharged particles and molecular aggregates. This paper describes the chamber, associated equipment and method of operation and discusses the performance of the system.
A circuit for the measurement of instantaneous temperature in heated turbulent flows
Authors: S Tavoularis
Published: July 2002

Measurement of the instantaneous temperature in heated turbulent air flows has often been carried out with cold-wires operating at a constant current supplied by an electronic circuit. A new electronic circuit for such a resistance thermometer offering simplicity with good accuracy, has been developed. The advantages over previous configurations are low voltage drift and simple construction and operation. The circuit is described in detail and measurements in a heated homogeneous shear flow are provided as an application.
A high-power RF line generator of novel design
Authors: W N Hugrass  , I R Jones  , M G R Phillips
Published: July 2002

A modification of the Weibel radio frequency line generator is described. The modification substantially reduces the necessary number of spark gap switches and yields both a significant saving in construction costs and a greater ease of construction and reliability of operation. The construction and performance of an eight-period line generator incorporating this design modification are described. The equivalent root mean square open-circuit voltage and generator impedance are 14.1 kV and 9.7 Omega .
A reagent-efficient computer-controlled stopped-flow technique for electron spin resonance spectroscopy
Authors: P R C Gascoyne
Published: July 2002

A stopped-flow technique employing a mini-computer control arrangement is described for use in electron spin resonance spectroscopy. By observing the time dependence of small segments rather than individual points of a spectrum, complete time-resolved spectra in the range 10 ms to 5 min can be obtained with very efficient use of reagents. An algorithm and a suitable experimental arrangement are described for the application of the technique.
A sensitive apparatus for the reproducible measurement of fluorescence polarisation
Authors: R A Hann
Published: July 2002

Continuous measurements of fluorescence polarisation are made using a chopped light source and detected via a continuously rotating polariser. Lock-in amplification techniques are used to recover the information from the photomultiplier output, thus ensuring good stability and high signal-to-noise ratio.
Ion extraction from a plasma through a conical orifice
Authors: S V Krishna Kumar  , M C Siddagangappa  , V S Venkatasubramanian
Published: July 2002

A method of ion extraction from plasmas is reported in which the interference of field lines due to the extraction system in the plasma region is avoided by proper shaping of the extractor electrode and is supported by field plots.
Response time correlation for industrial temperature sensors
Authors: R K Chohan
Published: July 2002

Response time correlations relate response times and heat transfer coefficients. A simple relationship can be derived for industrial temperature sensors and is similar to that presented by Pandey (1985) for bare thermocouples. Some results of tests in validating this correlation are briefly presented.
A method for measuring plasma arc wind tunnel gas velocity with a position controlled electron beam probe
Authors: Charles Cason
Published: July 2002

An electron beam probe has been used in the Micom 8 MW Plasma Facility. Difficulties in applying the probe to measurements of such parameters as gas density were found to be caused by the weak plasma arc-generated magnetic fields producing positional displacements of the beam. This problem was solved by means of a closed-loop electronic controller. Response time of the controller is down 3 dB at 130 Hz; this was found to be sufficiently fast for adequate control. The operation of the controller indicated that 0·26 G magnetic field was induced in the flow stream by the arc jets. Gas velocity in a plasma flow was estimated by observation of the drift rate of pulsed beam-generated plasma cylinders as a phase shift from two observation points. Estimates of gas velocity for an air flow of 156 g s−1 from phase shift measurements gave 3700±400 m s−1 as compared with a machine computed value of 3800 m s−1 for a normalized specific total enthalpy of 150.
Rapid and accurate electrical resistivity measurements of bulk metal and alloy samples
Authors: J A Garcia  , S Hull  , S Messoloras  , R J Stewart
Published: July 2002

An inexpensive apparatus using the eddy current decay method for measuring the resistivity from bulk samples is described. In order to rapidly accumulate data on the variation of the eddy current, the analogue signal is digitised and stored in a specially developed fast transient device (FIFO). The digital data are then transferred to a microcomputer for further analysis. The resistivity of an Al-1.56 at.% Cu alloy has been measured using this apparatus in order to determine the solute concentration after different aging times at 210 degrees C.
Statistics of laser Doppler velocimeter signals: frequency measurement
Authors: R J Adrian
Published: July 2002

The statistical properties of laser Doppler velocimeter signals are derived and used to obtain the signal zero crossing statistics for steady flows and high scattering particle concentrations. The results are applied to a model of a zero crossing counter, and expressions for the power spectrum and autocorrelation of the output signal are given in terms of the input signal autocorrelation. The RMS value of the fluctuations in the zero crossing counter output is calculated as a function of the optical system bandwidth and the counting time for infinite and finite input signal-to-noise ratios, and simple asymptotic expressions are found for large counting times and infinite signal-to-noise ratio. For finite input signal-to-noise ratios and large counting times bounds are derived for the output of a zero crossing counter preceded by a tracking filter, and the effects of the tracking filter are discussed.
A pulsed nuclear magnetic resonance probe using a water thermostat
Authors: V S Steckline  , K F Kuhlmann  , W S Magee
Published: July 2002

A pulsed NMR probe with a doped-water thermostat is described. The sample temperature is held constant to +or-0.005 degrees C.
A simple compensating torquemeter for use in high field solenoids
Authors: C Voigt  , S Foner
Published: July 2002

A simple compensating torquemeter for use in high field solenoids is described. A capacitive pick up is used for sensing deviations from the zero position. The entire torquemeter is rotated in the axial field by means of a small worm gear assembly. Torques of 100 dyn cm can be measured to about 2%.
Pile-up corrections in the measurement of lifetimes
Authors: P B Coates
Published: July 2002

In lifetime and similar experiments is which the time interval is measured up to the first detected event, a pile-up error is introduced if subsequent events are neglected. The application of corrections at high data collection rates is discussed with reference to the second-order errors introduced by variations in the source intensity, which have not been considered previously, and coherence effects.
A facility for electron microscopy of specimens in controlled environments
Authors: P R Ward  , R F Mitchell
Published: July 2002

A controlled environment for specimens in the electron microscope is produced within a space formed by two 20 mu m apertures 0.75 mm apart in the gap of the objective polepiece. An additional diffusion pump makes it possible to operate the microscope with gas at 1 atm pressure in the space without covering the apertures with membranes. A side entry stage permits rapid specimen changing and enables the whole of a normal grid to be scanned. Preliminary experiments using this system indicate that repeat periods less than 100 AA can be distinguished in wet catalase when helium pressure is used in the specimen chamber and the current density at the specimen is 0.1 nA mu m-2 or less. With higher beam currents, bubbling occurs in the specimen and the structure of the crystal is no longer observable.
A small repetitive dye laser
Authors: C Loth  , R Astier  , Y H Meyer
Published: July 2002

A repetitive (up to 20 Hz) dye laser, was built for spectroscopic applications. Consuming only 60 W in a xenon flashtube which can operate continuously for several hours, it produces a monochromatic (2 AA) beam of tunable wavelength and with a divergence of 1 mrad. The peak power is about 0.5 kW. Coumarin derivatives and rhodamine 6G are tested in optimized solvents.
High voltage electron microscope specimen rod with demountable double tilting facilities
Authors: D L Allinson  , E Kisch
Published: July 2002

A double-tilting side-entry specimen rod which has sapphire bearings on one axis of tilt has been made. A feature of the device is the ability to remove and interchange the specimen mounting block.
Model calculations for the swept frequency acoustic resonator
Authors: S B Dev  , S Sarkar  , R A Pethrick
Published: July 2002

Describes a mathematical representation of elastic wave propagation in a swept frequency acoustic resonator. Conditions are investigated for the resonance of the cavity in a normal mode of vibration and limits presented for the frequency range over which this technique may be usefully used.
Calibration of a time-of-flight machine for molecular beam studies
Authors: H C W Beijerinck  , R G J M Moonen  , N F Verster
Published: July 2002

A time-of-flight machine for the velocity analysis of molecular beams is described together with an experimental investigation of systematic errors. A velocity selecting chopper is used to measure all delay times, including the delay in the beam detector due to the extraction time from the ionizer and the flight time of the ions in the quadrupole mass filter. With the ionizer no memory effects occur at emission currents smaller than 1 mA. Memory effects in the detector chamber due to the direct reflection of beam particles are eliminated.
Miniature Mattauch-Herzog mass spectrometer
Authors: J P Carrico  , S Booker  , J Rice  , E Schaefer
Published: July 2002

A miniature Mattauch-Herzog mass spectrometer is described. The electric field radius is 4.3 cm. Detector slits are placed in the magnet focal plane at positions corresponding to magnetic field radii of 1.0 and 2.5 cm. Information pertaining to the resolution and dynamic range is reported.
The literature of environmental communication
Authors: Pleasant Andrew , Good Jennifer , Shanahan James , Cohen Brad
Published: July 2002

This paper examines the growth and development of the literature of “environmental communication” research. The paper collects citations of all papers matching specified keywords covering environmental communication topics in the social science journal literature from relevant indices. The indices used were: the Institute for Scientific Information's (ISI) Social Sciences Citation Index (Web of Science), the ISI Arts and Humanities Citation Index (Web of Science), Communication Abstracts, PsycINFO, Anthropological Literature, Sociology Abstracts and Periodical Abstracts (Pro-Quest Direct). The paper analyzes the collected citations for journal of publication, date, and frequency of publication by year, author, and keywords and topics. The paper shows what topics of attention, what fields, and what journals have been interested in publishing environmental communication research, and some of the authors leading the way. In addition, basic topics of interest for environmental communication research are discerned. The literature review shows the need for a more centralized point of publication for environmental communication research.
Nonexpansive, 𝒯-continuous antirepresentations have common fixed points
Authors: Bartoszek Wojciech
Published: July 2002

Let

C
C

be a closed convex subset of a Banach (dual Banach) space

X

\mathfrak {X}

. By

S

\mathcal {S}

we denote an antirepresentation

{

T

s

:

s
∈
S
}

\{ T_{s} \,:\, s \in S \}

of a semitopological semigroup

S
S

as nonexpansive mappings on

C
C

. Suppose that the mapping

S
×
C
∋
(
s
,
x
)
→

T

s

x
∈
C

S \times C \ni (s,x) \to T_{s}x \in C

is jointly continuous when

C
C

has the weak (weak*) topology and the Banach space

R
U
C
(
S
)

RUC(S)

of bounded right uniformly continuous functions on

S
S

has a right invariant mean. If

C
C

is weakly compact (for some

x
∈
C

x \in C

the set

{

T

s

x

:

s
∈
S
}

¯

weak*

{\overline {\{ T_{s}x \,:\, s \in S \}}} ^{\text {weak*}}

is weakly* compact) and norm separable, then

{

T

s

:

s
∈
S
}

\{ T_{s} \,:\, s \in S \}

has a common fixed point in

C
C

.
On nonlinear oscillations in a suspension bridge system
Authors: Ding Zhonghai
Published: July 2002

In this paper, we study nonlinear oscillations in a suspension bridge system governed by two coupled nonlinear partial differential equations. By applying the Leray-Schauder degree theory, it is proved that the suspension bridge system has at least two solutions, one is a near-equilibrium oscillation, and the other is a large amplitude oscillation.
Determining the small solutions to 𝑆-unit equations
Authors: Smart N.
Published: July 2002

In this paper we generalize the method of Wildanger for finding small solutions to unit equations to the case of

S
S

-unit equations. The method uses a minor generalization of the LLL based techniques used to reduce the bounds derived from transcendence theory, followed by an enumeration strategy based on the Fincke-Pohst algorithm. The method used reduces the computing time needed from MIPS years down to minutes.
A topological characterisation of hyperbolic groups
Authors: Bowditch Brian
Published: July 2002

We characterise word hyperbolic groups as those groups which act properly discontinuously and cocompactly on the space of distinct triples of a compact metrisable space. This is, in turn, equivalent to a convergence group for which every point of the space is a conical limit point.
Branching theorems for compact symmetric spaces
Authors: Knapp A.
Published: July 2002

A compact symmetric space, for purposes of this article, is a quotient

G

/

K

G/K

, where

G
G

is a compact connected Lie group and

K
K

is the identity component of the subgroup of fixed points of an involution. A branching theorem describes how an irreducible representation decomposes upon restriction to a subgroup. The article deals with branching theorems for the passage from

G
G

to

K

2

×

K

1

K_{2}\times K_{1}

, where

G

/

(

K

2

×

K

1

)

G/(K_{2}\times K_{1})

is any of

U
(
n
+
m
)

/

(
U
(
n
)
×
U
(
m
)
)

U(n+m)/(U(n)\times U(m))

,

S
O
(
n
+
m
)

/

(
S
O
(
n
)
×
S
O
(
m
)
)

SO(n+m)/(SO(n)\times SO(m))

, or

S
p
(
n
+
m
)

/

(
S
p
(
n
)
×
S
p
(
m
)
)

Sp(n+m)/(Sp(n)\times Sp(m))

, with

n
≤
m

n\leq m

. For each of these compact symmetric spaces, one associates another compact symmetric space

G
′

/

K

2

G’/K_{2}

with the following property: To each irreducible representation

(
σ
,
V
)

(\sigma ,V)

of

G
G

whose space

V

K

1

V^{K_{1}}

of

K

1

K_{1}

-fixed vectors is nonzero, there corresponds a canonical irreducible representation

(

σ
′

,

V
′

)

(\sigma ’,V’)

of

G
′

G’

such that the representations

(
σ

|

K

2

,

V

K

1

)

(\sigma |_{K_{2}},V^{K_{1}})

and

(

σ
′

,

V
′

)

(\sigma ’,V’)

are equivalent. For the situations under study,

G
′

/

K

2

G’/K_{2}

is equal respectively to

(
U
(
n
)
×
U
(
n
)
)

/

diag
(
U
(
n
)
)

(U(n)\times U(n))/\text {diag}(U(n))

,

U
(
n
)

/

S
O
(
n
)

U(n)/SO(n)

, and

U
(
2
n
)

/

S
p
(
n
)

U(2n)/Sp(n)

, independently of

m
m

. Hints of the kind of “duality” that is suggested by this result date back to a 1974 paper by S. Gelbart.
Diacylglycerol Kinase δ Suppresses ER-to-Golgi Traffic via Its SAM and PH Domains
Authors: Nagaya Hisao , Wada Ikuo , Jia Yan-Jun , Kanoh Hideo
Published: July 2002

We report here that the anterograde transport from the endoplasmic reticulum (ER) to the Golgi was markedly suppressed by diacylglycerol kinase δ (DGKδ) that uniquely possesses a pleckstrin homology (PH) and a sterile α motif (SAM) domain. A low-level expression of DGKδ in NIH3T3 cells caused redistribution into the ER of the marker proteins of the Golgi membranes and the vesicular-tubular clusters (VTCs). In this case DGKδ delayed the ER-to-Golgi traffic of vesicular stomatitis virus glycoprotein (VSV G) and also the reassembly of the Golgi apparatus after brefeldin A (BFA) treatment and washout. DGKδ was demonstrated to associate with the ER through its C-terminal SAM domain acting as an ER-targeting motif. Both of the SAM domain and the N-terminal PH domain of DGKδ were needed to exert its effects on ER-to-Golgi traffic. Kinase-dead mutants of DGKδ were also effective as the wild-type enzyme, suggesting that the catalytic activity of DGK was not involved in the present observation. Remarkably, the expression of DGKδ abrogated formation of COPII-coated structures labeled with Sec13p without affecting COPI structures. These findings indicate that DGKδ negatively regulates ER-to-Golgi traffic by selectively inhibiting the formation of ER export sites without significantly affecting retrograde transport.
Black-White Inequalities in Mortality and Life Expectancy, 1933–1999: Implications for Healthy People 2010
Authors: Levine Robert S. , Foster James E. , Fullilove Robert E. , Fullilove Mindy T. , Briggs Nathaniel C. , Hull Pamela C. , Husaini Baqar A. , Hennekens Charles H.
Published: July 2002

Objectives.

Optimistic predictions for the Healthy People 2010 goals of eliminating racial/ethnic disparities in health have been made based on absolute improvements in life expectancy and mortality. This study sought to determine whether there is evidence of relative improvement (a more valid measure of inequality) in life expectancy and mortality, and whether such improvement, if demonstrated, predicts future success in eliminating disparities.

Methods.

Historical data from the National Center for Health Statistics and the Census Bureau were used to predict future trends in relative mortality and life expectancy, employing an Autoregressive Integrated Moving Average (ARIMA) model. Excess mortality and time lags in mortality and life expectancy for blacks relative to whites were also estimated.

Results.

Based on data for 1945 to 1999, forecasts for relative black:white age-adjusted, all-cause mortality and white:black life expectancy at birth showed trends toward increasing disparities. From 1979, when the Healthy People initiative began, to 1998, the black:white ratio of age-adjusted, gender-specific mortality increased for all but one of nine causes of death that accounted for 83.4% of all US mortality in 1998. From 1980 to 1998, average numbers of excess deaths per day among American blacks relative to whites increased by 20%. American blacks experienced 4.3 to 4.5 million premature deaths relative to whites in 1940–1999.

Conclusions.

The rationale that underlies the optimistic Healthy People 2010 forecasts, that future success can be built on a foundation of past success, is not supported when relative measures of inequality are used. There has been no sustained decrease in black-white inequalities in age-adjusted mortality or life expectancy at birth at the national level since 1945. Without fundamental changes, most probably related to the ways medical and public health practitioners are trained, evaluated, and compensated for prevention-related activities, as well as further research on translating the findings of prevention studies into clinical practice, it is likely that simply reducing disparities in access to care and/or medical treatment will be insufficient. Millions of premature deaths will continue to occur among African Americans.
Factors Associated with Adolescent Initiation of Injection Drug Use
Authors: Fuller Crystal M. , Vlahov David , Arria Amelia M. , Ompad Danielle C. , Garfein Richard , Strathdee Steffanie A.
Published: July 2002

Objective.

The purpose of this study was to evaluate the extent to which demographic, sexual, and non-injection drug use practices predict adolescent initiation of injection drug use.

Methods.

Street recruited injection drug users 15–30 years of age in Baltimore, Maryland, who initiated injection within five years of study enrollment, completed a questionnaire that included a year-by-year history regarding the five years prior to initiation of injection. Factors associated with initiation during adolescence (≤21 years of age) versus young adult-hood (>21) were determined using logistic regression.

Results.

Of 226 participants, most were female (61%) and African American (64%). Median age of participants was 25; median age at initiation of injection was 23. Factors significantly associated with adolescent initiation in multivariate analysis included race other than African American, and practices prior to initiating injection including condom use, lack of cocaine use, exclusive crack smoking just prior to initiation, and smoking marijuana. Adolescent initiates also had shorter durations of illicit drug use prior to initiating injection.

Conclusion.

Short-term non-injection drug use, particularly exclusive crack smoking, was associated with adolescent initiation of injection drug use. Early prevention efforts targeting this high-risk group of younger drug users are warranted in order to delay or prevent onset of injection drug use.
Profile of Arthritis Disability
Authors: Verbrugge Lois M. , Juarez Lucia
Published: July 2002

Using the 1994–95 National Health Interview Supplement Disability Supplement, the authors study levels of disabilities and accommodations among US adults with arthritis disability, compared to people with disability due to other conditions.

Arthritis-disabled people are defined in two ways. One definition covers a broad range of arthritis and rheumatic conditions, and the other concentrates solely on arthritis.

The authors find that arthritis-disabled people have more total disabilities than other-disabled people. However, their disabilities are less severe, have shorter durations, and accumulate more gradually over time. Despite more disabilities, people with arthritis disability use fewer assistive and service accommodations than other-disabled people. They do use more mobility aids.

Because arthritis is the leading chronic condition for middle-aged and older adults, this profile of extensive but mild-to-moderate disability is experienced by many millions of adults. Accommodations for arthritis may also be extensive but aimed more toward self-care than toward assistive and medical services.
Safer Choices: Reducing Teen Pregnancy, HIV, and STDs
Authors: Coyle Karin , Basen-Engquist Karen , Kirby Douglas , Parcel Guy , Banspach Stephen , Collins Janet , Baumler Elizabeth , Carvajal Scott , Harrist Ronald
Published: July 2002

Objectives.

This study evaluated the long-term effectiveness of Safer Choices, a theory-based, multi-component educational program designed to reduce sexual risk behaviors and increase protective behaviors in preventing HIV, other STDs, and pregnancy among high school students.

Methods.

The study used a randomized controlled trial involving 20 high schools in California and Texas. A cohort of 3869 ninth-grade students was tracked for 31 months from fall semester 1993 (baseline) to spring semester 1996 (31-month follow-up). Data were collected using self-report surveys administered by trained data collectors. Response rate at 31-month follow-up was 79%.

Results.

Safer Choices had its greatest effect on measures involving condom use. The program reduced the frequency of intercourse without a condom during the three months prior to the survey, reduced the number of sexual partners with whom students had intercourse without a condom, and increased use of condoms and other protection against pregnancy at last intercourse. Safer Choices also improved 7 of 13 psychosocial variables, many related to condom use, but did not have a significant effect upon rates of sexual initiation.

Conclusions.

The Safer Choices program was effective in reducing important risk behaviors for HIV, other STDs, and pregnancy and in enhancing most psychosocial determinants of such behavior.
in vivo gene expression and the adaptive response: from pathogenesis to vaccines and antimicrobials
Authors: Heithoff Douglas M. , Sinsheimer Robert L. , Low David A. , Mahan Michael J.
Published: July 2002

Microbial pathogens possess a repertoire of virulence determinants that each make unique contributions to fitness during infection. Analysis of these in vivo –expressed functions reveals the biology of the infection process, encompassing the bacterial infection strategies and the host ecological and environmental retaliatory strategies designed to combat them (e.g. thermal, osmotic, oxygen, nutrient and acid stress). Many of the bacterial virulence functions that contribute to a successful infection are normally only expressed during infection. A genetic approach was used to isolate mutants that ectopically expressed many of these functions in a laboratory setting. Lack of DNA adenine methylase (Dam) inSalmonella typhimuriumabolishes the preferential expression of many bacterial virulence genes in host tissues. Dam−Salmonellawere proficient in colonization of mucosal sites but were defective in colonization of deeper tissue sites. Additionally, Dam−mutants were totally avirulent and effective as live vaccines against murine typhoid fever. Since dam is highly conserved in many pathogenic bacteria that cause significant morbidity and mortality worldwide, Dams are potentially excellent targets for both vaccines and antimicrobials.
In‐phantom dosimetry for the reaction as a source for accelerator‐based BNCT
Authors: Burlon A. A. , Kreiner A. J. , White S. M. , Blackburn B. W. , Gierga D. P. , Yanch J. C.
Published: July 2002

The use of the reaction at MeV for accelerator‐based boron neutron capture therapy (AB‐BNCT) is investigated. Among the deuteron‐induced reactions at low incident energy, the reaction turns out to be one of the best for AB‐BNCT because of beneficial materials properties inherent to carbon and its relatively large neutron production cross section. The deuteron beam was produced by a tandem accelerator at MIT's Laboratory for Accelerator Beam Applications (LABA) and the neutron beam shaping assembly included a heavy water moderator and a lead reflector. The resulting neutron spectrum was dosimetrically evaluated at different depths inside a water‐filled brain phantom using the dual ionization chamber technique for fast neutrons and photons and bare and cadmium‐covered gold foils for the thermal neutron flux. The RBE doses in tumor and healthy tissue were calculated from experimental data assuming a tumor concentration of 40 ppm and a healthy tissue concentration of 11.4 ppm (corresponding to a reported ratio of 3.5:1). All results were simulated using the code MCNP, a general Monte Carlo radiation transport code capable of simulating electron, photon, and neutron transport. Experimental and simulated results are presented at 1, 2, 3, 4, 6, 8, and 10 cm depths along the brain phantom centerline. An advantage depth of 5.6 cm was obtained for a treatment time of 56 min assuming a 4 mA deuteron current and a maximum healthy tissue dose of 12.5 RBE Gy.
Development of an automated detection system for microcalcifications lesion in mammography (in Japanese)
Authors: Hirako Kenichi
Published: July 2002

An automated detection system for clustered microcalcifications in digital mammograms was developed for computer‐aided diagnosis (CAD) systems. We developed new detection filters of microcalcifications based on the gradient‐vector image analysis. The “triple‐ring filter” extracts the region in a pattern similar to that of a microcalcification shadow. Then the “variable‐ring filter” recalculates two vector‐feature values (vector‐direction and vector‐magnitude feature values) and determines the gray‐level threshold values adaptively. These filters significantly improved the diagnostic sensitivity for the detection of microcalcifications in comparison with our previously developed scheme based on image contrast analysis. It was proved by an F (free‐response) ROC examination: the true positive fraction of our new system was always 10% or more higher than our previous system while the number of false positives per image remained constant. We also developed a “contrast‐correction technique” to correct the effects of the background content (mammary gland tissue) around the microcalcification and film contrast characteristic on its image contrast. This scheme improved the diagnostic performance for detecting the microcalcifications, and its technology was applied to the image data of two facilities where the imaging characteristic in terms of contrast was different. The diagnostic sensitivity for the detection of clustered microcalcifications in our database of 165 mammograms was 94.3% with 0.63 false positives per image, which demonstrates the effectiveness of our method. In addition, we also propose to use an artificial neural network to detect the microcalcifications in the first step instead of the triple‐ring filter method: this may make it possible to develop a CAD system with an even higher detection performance level.
Site‐specific variability in trabecular bone dosimetry: Considerations of energy loss to cortical bone
Authors: Patton P. W. , Rajon D. A. , Shah A. P. , Jokisch D. W. , Inglis B. A. , Bolch W. E.
Published: July 2002

With continual advances in radionuclide therapies, increasing emphasis is being placed on improving the patient specificity of dose estimates to marrow tissues. While much work has been focused on determining patient‐specific assessments of radionuclide uptake in the skeleton, few studies have been initiated to explore the individual variability of absorbed fraction data for electron and beta‐particle sources in various skeletal sites. The most recent values of radionuclide S values used in clinical medicine continue to utilize a formalism in which electrons are transported under a trabecular bone geometry of infinite extent. No provisions are thus made for the fraction of energy lost to the cortical bone cortex of the skeletal site and its surrounding tissues. In the present study, NMR microscopy was performed on trabecular bone samples taken from the femoral head and humeral proximal epiphysis of three subjects: a 51‐year male, an 82‐year female, and an 86‐year female. Following image segmentation and coupling to EGS4, electrons were transported within macrostructural models of the various skeletal sites that explicitly include the spatial extent of the spongiosa, as well as the thickness of the surrounding cortical bone. These energy‐dependent profiles of absorbed fractions to marrow tissues were then compared to transport simulations made within an infinite region of spongiosa. Ratios of mean absorbed fraction, as weighted by the beta energy spectra, under both transport methodologies were then assembled for the radionuclides and These ratios indicate that corrections to existing radionuclide S values for can vary by as much as 5% for the male, 6% for the 82‐year female, and 8% for the 86‐year female. For the higher‐energy beta spectrum of these same corrections can reach 8%, 10%, and 11%, respectively.
Investigations on dynamic intensity modulated photon fields in radiation therapy
Authors: Parsai Homayon
Published: July 2002

This thesis investigates the validity of inverse algorithms and delivery techniques in dynamic intensity modulated radiation therapy (IMRT) with the view toward clinical implementation. A dosimetric verification technique used to monitor the dynamic beam delivery was introduced with design considerations and clinical evaluation of various quality assurance (QA) phantoms, facilitating the measurement of dynamic IMRT dose distributions and conversion of photon fluence to machine deliverable monitor units. Benchmark tests using thermoluminescent dosimeters (TLDs), solid state detectors, and films were carried out in realistic clinical examples. This was to demonstrate the precision and degree of accuracy of the proposed techniques both in vitro and in vivo systems using canine subjects with paraspinal tumors. The results of the irradiation of canine subjects indicated that the goal of using IMRT to irradiate target volumes with sparing critical structures was met. However, the measure of physiological response found, was incapable of providing a more accurate measure of the dose delivered. Quantitative analysis on the influence of systematic and random field perturbations in highly conformal fields with emphasis on the dosimetric outcome is also presented in this thesis. Two sources of uncertainties deemed important in dynamic therapy of photon beams were studied. These were caused by inaccuracies in velocity and in position of both multileaf collimator (MLC) and backup diaphragms. This was attributed to some degree to the tolerance levels or mechanical constraints of beam defining parameters. These errors were simulated using a Gaussian function with standard deviation of ±1.0 mm to assess changes in dose distribution. Based on the results of this study, QA procedures which are unique to the delivery of dynamic beams were proposed.
Deblurring of x‐ray spectra acquired with a Nal‐photomultiplier detector by constrained least‐squares deconvolution
Authors: Skipper Julie A. , Hangartner Thomas N.
Published: July 2002

A constrained least‐squares technique to correct diagnostic x‐ray tube energy spectra for inherent blurring by scintillation detectors was developed. The measured detector response function to monoenergetic sources was used to construct a matrix that modeled the energy broadening in the crystal. This blurring operator, along with an estimate of statistical noise in the count data, comprised the a priori system knowledge required for application of the method. Tungsten anode spectra up to 90 kVp were acquired with a Nal‐photomultiplier detector system at a source‐to‐detector distance of 30 cm. X‐ray tube output was collimated at the detector by a 0.5 mm diameter pinhole collimator. Measured Nal spectra were compared to both published reference data and to spectra acquired in our laboratory with a Ge detector system. Application of the constrained least‐squares technique involved first defining a criterion function that combined an assessment of the goodness of fit with a weighted measure of the smoothness of the solution. Minimization of this function resulted in the corrected spectrum. While it is not possible to recover the characteristic tungsten peaks, the success of our method in deconvolving the measured spectra was demonstrated by a significant improvement in agreement with reference data. To provide a measure of this agreement, a histogram of the differences between the two curves was generated. The full width at half maximum (FWHM) of the Gaussian distribution fit to the histogram was used to quantify the similarity between the spectra and the reference data, both before and after correction. As spectral agreement improves, the FWHM becomes smaller. We show that application of the constrained least‐squares technique improved spectral matching by 20%–60%.
Nonideal projection data in x‐ray computed tomography (in English)
Authors: Ebert Matthias
Published: July 2002

This thesis deals with various aspects of x‐ray computed tomography (CT) from nonideal projection data that do not permit the successful application of standard image reconstruction methods. A versatile calibration method was implemented allowing an adequate correction for geometric flex effects introduced by nonideal geometry during data acquisition. A filtered backprojection algorithm was modified such that the geometric information from the calibration can be considered with high accuracy and in a computationally efficient way. The methods proposed here were evaluated by means of computer simulations and measurements using two experimental cone‐beam CT scanners. Results are presented that demonstrate their excellent performance. Furthermore, a new retrospective image restoration scheme was developed in order to tackle the problem of inconsistent projection data due to internal organ motion. This scheme was applied to simulated projections as well as clinical CT data of a beating heart. The results of these investigations indicate that the image restoration approach is a promising alternative to existing, well‐established image reconstruction methods if considerable organ motion occurs during data acquisition.
Computer simulation of time‐gated transillumination and reflection of biological tissues and tissuelike phantoms
Authors: Michielsen K. , De Raedt H. , Garcı́a N.
Published: July 2002

A simulation technique is employed to explore the possibility of locating millimeter‐sized objects, immersed in turbid media, from time‐gated measurements of the transmitted or reflected light. The simulation results for tissuelike phantoms are compared to experimental transillumination data and excellent agreement is found. Simulations of time‐gated reflection experiments show that it is possible to detect objects of 1 mm diameter. This may open new possibilities for medical diagnosis of breast cancer in an early stage.
New classes of helical weighting algorithms with applications to fast CT reconstruction
Authors: Besson Guy
Published: July 2002

The focus of this paper is on CT helical weighting algorithms using one source rotation, or 2π, worth of projection data. Currently known 2π helical weighting algorithms include a fan‐angle dependency, and do not lend themselves to fast reconstruction, for two reasons. First, it can be shown that the weight distributions present a line of discontinuity across the sinogram (projection space), which defines two separate sinogram regions. Second, the expressions for the weighting functions differ for those two regions. Accordingly, reconstruction of P different image planes (all using a given projection) requires P weightings and filterings of that projection. In this paper, it is shown that, by first generalizing the concept of the interpolation/extrapolation function used in the weighting, to the concept of distance function, and second by selecting particular classes of such distance functions, the discontinuity across the sinogram can be eliminated. By imposing specific sufficient conditions on such distance functions, single analytical expressions across the entire 2π sinogram are obtained. Decomposition of these particular “single” distance functions leads to two‐filtering reconstruction algorithms, for which a given projection needs to be filtered only two times for an arbitrary number P of reconstruction planes. Finally, another generalization of the concept of helical weighting leads to one‐filtering weight functions that depend only on the sum of the projection—and fan angles. Accordingly, after rebinning the fan‐beam projections to parallel projections, the corresponding 2π helical weighting algorithms do not include a dependency over the ray parameter. Equivalently, for these algorithms, weighting commutes with filtering, and reconstruction of an arbitrary number P of image planes requires only one filtering per projection. These algorithms are shown to be consistent with the hypothesis of a linear z variation of the projections.
Lens design for large‐area x‐ray sensitive vidicons
Authors: Pang G. , Luhta R. , Rowlands J. A.
Published: July 2002

Large‐area x‐ray sensitive vidicons have the potential to be superior to conventional x‐ray image intensifiers for medical fluoroscopy. To build a large‐area x‐ray vidicon, an electron lens system is necessary to provide perpendicular beam landing. In this paper, we discuss theoretically how to build two and three cylinder coaxial lenses for this purpose. Some general design rules and a preferred design which satisfies our design criteria are presented. Limitations of these simple types of electron lens are discussed. Two advanced designs for vidicons with short lengths or reduced beam landing error are also included. Among them, the deflection‐center‐change system is introduced here for the first time.
Forward and adjoint methods for radiotherapy planning
Authors: Difilippo Felix C.
Published: July 2002

The sensitivity theory developed for nuclear engineering applications is applied to radiotherapy planning. After emphasizing the mathematical equivalence of solving the Boltzmann equation in forward and adjoint spaces both mathematical approaches are implemented to calculate the sensitivities of the dose distributions in a mathematical phantom to changes in the source of radiation. The tagging of the functionals of the radiation field with the origin of the source (forward or adjoint) makes possible the calculation of the sensitivity of the dose to the position, angular distribution, intensity, and spectra of the source, in a very efficient way by using present day available codes and hardware. There is then a potential for a new, accurate and potentially faster method that does not rely on a trial and error methodology.
The volume effect in irradiated mouse colorectum
Authors: Skwarchuk Mark William
Published: July 2002

One approach for decreasing rectal complications due to prostate irradiation is to reduce the volume of normal tissue irradiated using conformal radiotherapy. A number of mathematical models have been previously developed to describe the change in associated toxicity with a change in irradiated volume, i.e., the “volume effect,” for serial‐type normal tissues, including the rectum. However, limited data are available to test or support these models. One goal of this thesis was to test the hypothesis that there would not be a threshold length, as predicted by the Probability model of the volume effect, in the development of fibrotic obstruction after irradiation of various lengths of C57B1/6 and C3Hf/Kam mouse colorectum. A strain‐dependent threshold length was observed, in contradiction of the Probability model predictions. However, the data could be described if the Probability model was modified to include a threshold volume term, i.e., the Threshold Probability model. The mechanism of the threshold was determined to be epithelial regeneration after irradiation. Strain differences were observed for the incidence, histological time of appearance, and spatial location of fibrosis. However, there were no consistent strain differences in mRNA levels or immunolocalization for the pro‐fibrotic cytokines TGFbeta 1, 2, 3, and TNFalpha. The data indicate the need for volume effect models that account for biologically important processes, such as the effect of epithelial regeneration after irradiation.
Clinically shaped fields: Relative outputs for Varian multileaf collimators and tray‐mounted cerrobend blocks
Authors: Meyer Klaudia H. , Skubic Stanley E. , Baird Leemon C. , Virudachalam Ramasamy , Asche David R.
Published: July 2002

The purpose of this study was to determine the variation in relative output factors for fields shaped using a multileaf collimator (MLC) versus tray‐mounted cerrobend blocks. A total of 21 different clinical fields from 16 patients were compared by casting cerrobend blocks from the same films that had generated the MLC shapes. Output measurements were made on a Varian 2300CD (26 1 cm leaves per side) in solid water for 6 and 20 MV at source‐to‐axis‐distance (SAD=100 cm) and at two depths, 5 cm and the clinically prescribed depth All measurements were taken under the central axis of the beam unless the shaped field was obviously skewed off axis or the beam was split. Several cases were repeated on a Varian 2100CD (40 1 cm leaves per side) MLC. For the 21 cases studied, the average overall MLC factor (MLC reading divided by the block reading) was found to be 0.9952 with a standard deviation of 0.0024. Repeat measurements performed on the 2100CD were within 0.2% of the MLC factors measured (for the same fields) on the 2300CD. When the data are broken down in terms of clinical applications (type of case at a clinically prescribed depth and energy), the resulting total clinical average is 0.9957 with a standard deviation of 0.0022. Both the overall average and the total clinical average MLC factors (0.995–0.996) agree with previous literature, which used abstract or generic field shapes. Further investigation of the data from this study may find a correlation between the MLC factor and the percent of open field.
Dependence of scatter on atomic number for x rays from tungsten and molybdenum anodes in the mammographic energy range
Authors: Aus R. J. , DeWerd L. A. , Pearson D. W. , Micka J. A. , Ng K. H.
Published: July 2002

A study was done to determine the relative amounts of scatter for the following materials with atomic numbers ranging from to C, Al, Ti, Fe, Cu, Zn, Zr, Y, Mo, Ta, and Pb. Measurements were performed for each material on two constant potential x‐ray units—one fitted with a molybdenum (Mo) anode–Mo filter and the other with a tungsten (W) anode–aluminum (Al) filter (medium filtration) at 30 kVp. Theoretical calculations were also performed for each anode to explain the scatter behavior and to aid in predicting the behavior for materials where measurements were not made. There was good agreement between the theoretical calculations and the experimental data.
Assessment of the relative dose distribution around an line source using a liquid ionization chamber
Authors: Bahar‐Gogani Jalil , Wickman Göran , Johansson Lennart , Johansson Bengt Erik
Published: July 2002

The relative absorbed dose distribution in water around an line source of 50 mm length and 0.3 mm diam has been measured using a liquid ionization chamber (LIC). The sensitive volume of the chamber is a cylinder with 3.0 mm diam and a thickness of 1.0 mm. The sensitive medium in the LIC consists of a mixture of two dielectric liquids, tetramethylsilane and isooctane. The mixture has been optimized so that the LIC provides an almost energy‐independent response for the radiation qualities present at different distances from the source in water. The measurements were carried out at distances of 2.5–50.0 mm along the source bisector and at distances of 0.0 to ±40.0 mm along the source axis. The results were compared with measurements made with LiF chips in Solid Water and with calculated data based on an analytical solution to the Sievert integral as well as with Monte Carlo calculations of absolute dose rate in water. Considering the uncertainties involved, the dose distribution measured by the LIC is in reasonably good agreement with the theoretical data as well as the results held with LiF. In comparison with the Monte Carlo calculations the discrepancies range from 0.1% to 18% with the largest differences at points close to the source. This work demonstrates the ability of the LIC for mapping the dose distribution around a low‐dose‐rate brachytherapy source emitting photons of intermediate energies.