bluuebunny/crossref_metadata_2025 huggingface dataset:
Kernel of locally nilpotent 𝑅-derivations of 𝑅[𝑋,𝑌]
Authors: Bhatwadekar S. , Dutta Amartya
Published: July 2002

In this paper we study the kernel of a non-zero locally nilpotent

R
R

-derivation of the polynomial ring

R
[
X
,
Y
]

R[X,Y]

over a noetherian integral domain

R
R

containing a field of characteristic zero. We show that if

R
R

is normal then the kernel has a graded

R
R

-algebra structure isomorphic to the symbolic Rees algebra of an unmixed ideal of height one in

R
R

, and, conversely, the symbolic Rees algebra of any unmixed height one ideal in

R
R

can be embedded in

R
[
X
,
Y
]

R[X,Y]

as the kernel of a locally nilpotent

R
R

-derivation of

R
[
X
,
Y
]

R[X,Y]

. We also give a necessary and sufficient criterion for the kernel to be a polynomial ring in general.
Asymptotics for minimal discrete energy on the sphere
Authors: Kuijlaars A. , Saff E.
Published: July 2002

We investigate the energy of arrangements of

N
N

points on the surface of the unit sphere

S
d

S^d

in

R

d
+
1

\mathbf {R}^{d+1}

that interact through a power law potential

V
=
1

/

r
s

,

V = 1/r^s ,

where

s
>
0

s > 0

and

r
r

is Euclidean distance. With

E

d

(
s
,
N
)

\mathcal {E}_d(s,N)

denoting the minimal energy for such

N
N

-point arrangements we obtain bounds (valid for all

N
N

) for

E

d

(
s
,
N
)

\mathcal {E}_d(s,N)

in the cases when

0
>
s
>
d

0 > s > d

and

2
≤
d
>
s

2 \leq d > s

. For

s
=
d

s = d

, we determine the precise asymptotic behavior of

E

d

(
d
,
N
)

\mathcal {E}_d(d,N)

as

N
→
∞

N \rightarrow \infty

. As a corollary, lower bounds are given for the separation of any pair of points in an

N
N

-point minimal energy configuration, when

s
≥
d
≥
2

s \geq d \geq 2

. For the unit sphere in

R

3

\mathbf {R}^3

(
d
=
2
)

(d = 2)

, we present two conjectures concerning the asymptotic expansion of

E

2

(
s
,
N
)

\mathcal {E}_2(s,N)

that relate to the zeta function

ζ
L

(
s
)

\zeta _L(s)

for a hexagonal lattice in the plane. We prove an asymptotic upper bound that supports the first of these conjectures. Of related interest, we derive an asymptotic formula for the partial sums of

ζ
L

(
s
)

\zeta _L(s)

when

0
>
s
>
2

0 > s > 2

(the divergent case).
Generators and irreducible polynomials over finite fields
Authors: Wan Daqing
Published: July 2002

Weil’s character sum estimate is used to study the problem of constructing generators for the multiplicative group of a finite field. An application to the distribution of irreducible polynomials is given, which confirms an asymptotic version of a conjecture of Hansen-Mullen.
On the rapid computation of various polylogarithmic constants
Authors: Bailey David , Borwein Peter , Plouffe Simon
Published: July 2002

We give algorithms for the computation of the

d
d

-th digit of certain transcendental numbers in various bases. These algorithms can be easily implemented (multiple precision arithmetic is not needed), require virtually no memory, and feature run times that scale nearly linearly with the order of the digit desired. They make it feasible to compute, for example, the billionth binary digit of

log
⁡

(
2
)

\log {(2)}

or

π
\pi

on a modest work station in a few hours run time. We demonstrate this technique by computing the ten billionth hexadecimal digit of

π
\pi

, the billionth hexadecimal digits of

π

2

,

log
⁡
(
2
)

\pi ^{2}, \; \log (2)

and

log

2

⁡
(
2
)

\log ^{2}(2)

, and the ten billionth decimal digit of

log
⁡
(
9

/

10
)

\log (9/10)

. These calculations rest on the observation that very special types of identities exist for certain numbers like

π
\pi

,

π

2

\pi ^{2}

,

log
⁡
(
2
)

\log (2)

and

log

2

⁡
(
2
)

\log ^{2}(2)

. These are essentially polylogarithmic ladders in an integer base. A number of these identities that we derive in this work appear to be new, for example the critical identity for

π
\pi

:
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="pi equals sigma-summation Underscript i equals 0 Overscript normal infinity Endscripts StartFraction 1 Over 16 Superscript i Baseline EndFraction left-parenthesis StartFraction 4 Over 8 i plus 1 EndFraction minus StartFraction 2 Over 8 i plus 4 EndFraction minus StartFraction 1 Over 8 i plus 5 EndFraction minus StartFraction 1 Over 8 i plus 6 EndFraction right-parenthesis period">

π
=

∑

i
=
0

∞

1

16

i

(

4

8
i
+
1

−

2

8
i
+
4

−

1

8
i
+
5

−

1

8
i
+
6

)

.

\begin{equation*}\pi = \sum _{i=0}^{\infty }\frac {1}{16^{i}}\bigr ( \frac {4}{8i+1} - \frac {2}{8i+4} - \frac {1}{8i+5} - \frac {1}{8i+6} \bigl ).\end{equation*}
Evaluation of discrete logarithms in a group of 𝑝-torsion points of an elliptic curve in characteristic 𝑝
Authors: Semaev I.
Published: July 2002

We show that to solve the discrete log problem in a subgroup of order

p
p

of an elliptic curve over the finite field of characteristic

p
p

one needs

O
(
ln
⁡
p
)

O(\ln p)

operations in this field.
Stretch-regulated Exocytosis/Endocytosis in Bladder Umbrella Cells
Authors: Truschel Steven T. , Wang Edward , Ruiz Wily G. , Leung Som-Ming , Rojas Raul , Lavelle John , Zeidel Mark , Stoffer David , Apodaca Gerard
Published: July 2002

The epithelium of the urinary bladder must maintain a highly impermeable barrier despite large variations in urine volume during bladder filling and voiding. To study how the epithelium accommodates these volume changes, we mounted bladder tissue in modified Ussing chambers and subjected the tissue to mechanical stretch. Stretching the tissue for 5 h resulted in a 50% increase in lumenal surface area (from ∼2900 to 4300 μm2), exocytosis of a population of discoidal vesicles located in the apical cytoplasm of the superficial umbrella cells, and release of secretory proteins. Surprisingly, stretch also induced endocytosis of apical membrane and 100% of biotin-labeled membrane was internalized within 5 min after stretch. The endocytosed membrane was delivered to lysosomes and degraded by a leupeptin-sensitive pathway. Last, we show that the exocytic events were mediated, in part, by a cyclic adenosine monophosphate, protein kinase A-dependent process. Our results indicate that stretch modulates mucosal surface area by coordinating both exocytosis and endocytosis at the apical membrane of umbrella cells and provide insight into the mechanism of how mechanical forces regulate membrane traffic in nonexcitable cells.
GOLD—Graphical Overview of Linkage Disequilibrium
Authors: Abecasis G. R. , Cookson W. O. C.
Published: July 2002

Summary: We describe a software package that provides a graphical summary of linkage disequilibrium in human genetic data. It allows for the analysis of family data and is well suited to the analysis of dense genetic maps.

Availability: http://www.well.ox.ac.uk/asthma/GOLD

Contact: goncalo@well.ox.ac.uk
gff2ps: visualizing genomic annotations
Authors: Abril Josep F. , Guigó Roderic
Published: July 2002

Summary: gff2psis a program for visualizing annotations of genomic sequences. The program takes the annotated features on a genomic sequence in GFF format as input, and produces a visual output in PostScript. While it can be used in a very simple way, it also allows for a great degree of customization through a number of options and/or customization files.

Availability: gff2psis freely available at http://www1.imim.es/~jabril/GFFTOOLS/GFF2PS.html

Contact: jabril@imim.es

Supplementary information: http://www1.imim.es/~jabril/GFFTOOLS/GFF2PS.html

To whom correspondence should be addressed.
Statistical estimation of cluster boundaries in gene expression
profile data
Authors: Horimoto Katsuhisa , Toh Hiroyuki
Published: July 2002

Motivation: Gene expression profile data are rapidly accumulating due to advances in microarray techniques. The abundant data are analyzed by clustering procedures to extract the useful information about the genes inherent in the data. In the clustering analyses, the systematic determination of the boundaries of gene clusters, instead of by visual inspection and biological knowledge, still remains challenging.

Results: We propose a statistical procedure to estimate the number of clusters in the hierarchical clustering of the expression profiles. Following the hierarchical clustering, the statistical property of the profiles at the node in the dendrogram is evaluated by a statistics-based value: the variance inflation factor in the multiple regression analysis. The evaluation leads to an automatic determination of the cluster boundaries without any additional analyses and any biological knowledge of the measured genes. The performance of the present procedure is demonstrated on the profiles of 2467 yeast genes, with very promising results.

Availability: A set of programs will be electronically sent upon request.

Contact: horimoto@post.saga-med.ac.jp; toh@beri.co.jp

* To whom all correspondence should be addressed.

† These authors contributed equally to this work.
Comparison of genomic DNA sequences: solved and unsolved

problems
Authors: Miller Webb
Published: July 2002

Motivation: The DNA sequences of entire genomes are being determined at a rapid rate. Whereas initial genome sequencing efforts were for organisms chosen to be widely spaced in the tree of life, there is a growing emphasis on projects to sequence a species that is sufficiently similar to an already-sequenced species to allow direct comparison of those two DNA sequences. This and other changes in genome sequencing strategies have created a strong need for new methods to compare genomic sequences.

Results: We sketch the current state of software for comparing genomic DNA sequences and outline research directions that we believe are likely to result in important advances in practice.

Contact: webb@cse.psu.edu
THE EFFECTS OF SECONDARY SCHOOL QUALITY ON THE DISTRIBUTION OF EARNINGS
Authors: Eide Eric R. , Showalter Mark H. , Sims David P.
Published: July 2002

A number of researchers have investigated the effects of school quality on average earnings in the postschooling years. In this article we broaden the discussion to investigate whether school quality has a measurable impact at other points in the conditional earnings distribution. We find that in specifications that do not control for individual and family background characteristics there are differential effects of school resources on earnings. The most significant effects occur in the top half of the conditional earnings distribution. However, after controlling for a variety of demographic variables, much of the impact of school resources on earnings is diminished. Exceptions to this seem to be school enrollment levels and, to a lesser degree, expenditures: higher enrollments tend to raise the upper tail of the earnings distribution without a similar increase in the bottom of the distribution; the effect of expenditures is positive and significant for the 0.25 quantile and the median.
Impact of the six nucleotides downstream of the stop codon on translation termination
Authors: Namy Olivier , Hatin Isabelle , Rousset Jean‐Pierre
Published: July 2002

The efficiency of translation termination is influenced by local contexts surrounding stop codons. In Saccharomyces cerevisiae, upstream and downstream sequences act synergistically to influence the translation termination efficiency. By analysing derivatives of a leaky stop codon context, we initially demonstrated that at least six nucleotides after the stop codon are a key determinant of readthrough efficiency in S. cerevisiae. We then developed a combinatorial‐based strategy to identify poor 3′ termination contexts. By screening a degenerate oligonucleotide library, we identified a consensus sequence –CA(A/G)N(U/C/G)A–, which promotes >5% readthrough efficiency when located downstream of a UAG stop codon. Potential base pairing between this stimulatory motif and regions close to helix 18 and 44 of the 18S rRNA provides a model for the effect of the 3′ stop codon context on translation termination.
Physical and functional association of SU(VAR)3‐9 and HDAC1 in Drosophila
Authors: Czermin Birgit , Schotta Gunnar , Hülsmann Bastian B , Brehm Alexander , Becker Peter B , Reuter Gunter , Imhof Axel
Published: July 2002

Modification of histones can have a dramatic impact on chromatin structure and function. Acetylation of lysines within the N‐terminal tail of the histone octamer marks transcriptionally active regions of the genome whereas deacetylation seems to play a role in transcriptional silencing. Recently, the methylation of the histone tails has also been shown to be important for transcriptional regulation and chromosome structure. Here we show by immunoaffinity purification that two activities important for chromatin‐mediated gene silencing, the histone methyltransferase SU(VAR)3‐9 and the histone deacetylase HDAC1, associate in vivo. The two activities cooperate to methylate pre‐acetylated histones. Both enzymes are modifiers of position effect variegation and interact genetically in flies. We suggest a model in which the concerted histone deacetylation and methylation by a SU(VAR)3‐9/HDAC1‐containing complex leads to a permanent silencing of transcription in particular areas of the genome.
A review of the comparative in-vitro activities of 12 antimicrobial agents, with a focus on five new ‘respiratory quinolones’
Authors: Blondeau Joseph M.
Published: July 2002

The efficacies of many antimicrobial agents are being threatened by a global increase in the numbers of resistant bacterial pathogens—microorganisms that were once susceptible to some of these agents. In particular, antimicrobial resistance amongst strains of Haemophilus influenzae,Moraxella catarrhalis and Streptococcus pneumoniae has limited the usefulness of first-line agents in some clinical settings. Quinolones were introduced in the 1980s and represented a significant therapeutic advancement in the treatment of patients with infectious diseases. While these compounds possessed potent in-vitro activities against a wide range of Gram-negative pathogens, their activities against some Gram-positive and ‘ atypical’ pathogens remained borderline. Further advancement in the development of quinolones has overcome some of these problems. The ‘respiratory quinolones’ represent a new generation within this class of molecules and comprise compounds possessing broad spectrum activities against Gram-negative, Gram-positive and atypical pathogens. This review will focus on the in-vitro activities of five new respiratory quinolones (gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin and trovafloxacin), ciprofloxacin and six non-quinolone agents (azithromycin, clarithromycin, amoxycillin, co-amoxiclav, cefuroxime and co-trimoxazole) against a range of bacterial and atypical pathogens, including those that are now resistant to several of these compounds.
Herpes zoster—predicting and minimizing the impact of post-herpetic neuralgia
Authors: Johnson Robert W.
Published: July 2002

Herpes zoster results from reactivation of latent varicella-zoster virus in the dorsal root ganglia and is frequently associated with severe pain. Most patients suffer acute pain during the rash phase, and in many, prodromal pain or discomfort also precedes the rash. The pain of herpes zoster gradually resolves with time, but may persist after the acute disease as post-herpetic neuralgia for weeks, months or even years. Post-herpetic neuralgia, the most common complication of herpes zoster, often results in significant morbidity and healthcare resource usage. Early treatment with oral antivirals has been shown to accelerate the resolution of postherpetic neuralgia, with therapeutic effects particularly evident in the over-50 age group, where pain generally persists for longer. Progressively increasing life expectancy of the population translates to increasing numbers of cases of herpes zoster. The socio-economic gains associated with active management, including use of oral antivirals where indicated, to speed resolution of pain and post-herpetic neuralgia, readily justify additional cost.
Teens' Images of Smoking and Smokers
Authors: Luke Douglas , Allen Peg , Arian Gretchen , Crawford Myra , Headen S. , Spigner C. , Tassler P. , Ureda J.
Published: July 2002

The authors used qualitative and quantitative data to identify and interpret specific images teens have about smoking and smokers. Qualitative data were collected in 1996 from 793 teenagers participating in 125 focus groups at eight different sites across the United States.

Most focus groups were homogeneous with respect to gender, ethnicity, and smoking status. Ages ranged from 12 to 18 years, and about half of the participants were female. The majority of participants (62%) were white and African American, the remainder (38%) were Hispanic, American Indian, and Asian/Pacific Islander. Groups were comprised of smoking and nonsmoking teens. Focus group activities were used to elicit image-related discussions about attitudes, beliefs, and perceptions of smoking.

Investigators identified seven consistent and distinctive image themes: Appearance (smoking is dirty and unattractive), Activity (nonsmokers have busy, active lives), Drugs and sex (smokers are substance abusers and are sexually active), Rebellion (smokers belong to rebellious groups), Affect (smokers are depressed, angry, and stressed-out), In control (nonsmokers have self-control and are independent), and Pride (nonsmokers are proud of themselves, their families, and their heritage).

A large scale, multi-site qualitative research approach can increase understanding of teen smoking. The identification of distinctive images of smoking can help researchers develop more sophisticated models of the processes of teen smoking than currently exist.
Quality of Data in Multiethnic Health Surveys
Authors: Pasick Rena J. , Stewart Susan L. , Bird Joyce A. , D'Onofrio Carol N.
Published: July 2002

Objective.

There has been insufficient research on the influence of ethno-cultural and language differences in public health surveys. Using data from three independent studies, the authors examine methods to assess data quality and to identify causes of problematic survey questions.

Methods.

Qualitative and quantitative methods were used in this exploratory study, including secondary analyses of data from three baseline surveys (conducted in English, Spanish, Cantonese, Mandarin, and Vietnamese). Collection of additional data included interviews with investigators and interviewers; observations of item development; focus groups; think-aloud interviews; a test-retest assessment survey; and a pilot test of alternatively worded questions.

Results.

The authors identify underlying causes for the 12 most problematic variables in three multiethnic surveys and describe them in terms of ethnic differences in reliability, validity, and cognitive processes (interpretation, memory retrieval, judgment formation, and response editing), and differences with regard to cultural appropriateness and translation problems.

Conclusions.

Multiple complex elements affect measurement in a multiethnic survey, many of which are neither readily observed nor understood through standard tests of data quality. Multiethnic survey questions are best evaluated using a variety of quantitative and qualitative methods that reveal different types and causes of problems.
The Contributions of Managed Care Plans to Public Health Practice: Evidence from the Nation's Largest Local Health Departments
Authors: Mays Glen P. , Halverson Paul K. , Stevens Rachel
Published: July 2002

Objective.

The authors examine the extent and nature of managed care plans participating in local public health activities.

Methods.

In 1998, the authors surveyed the directors of all US local health departments serving jurisdictions of at least 100,000 residents to collect information about public health activities performed in their jurisdictions and about organizations participating in the activities. Multivariate logistic and linear regression models were used to examine organizational and market characteristics associated with managed care plan participation in public health activities.

Results.

Managed care plans were reported to participate in public health activities in 164 (46%) of the jurisdictions surveyed, and to contribute to 13% of the public health activities performed in the average jurisdiction. Plans appeared most likely to participate in public health activities involving the delivery or management of personal health services and the exchange of health-related information. Managed care participation was more likely to occur in jurisdictions with higher HMO penetration, fewer competing plans, and larger proportions of plans enrolling Medicaid recipients. Participation was positively associated with the overall scope and perceived effectiveness of local public health activities.

Conclusions.

Although plans participate in a narrow range of activities, these contributions may complement the work of public health agencies.
Telehealth: Reaching Out to Newly Injured Spinal Cord Patients
Authors: Phillips V. L. , Vesmarovich Susan , Hauber Roxanne , Wiggers Edith , Egner Amanda
Published: July 2002

Objectives.

The authors present preliminary results on health-related outcomes of a randomized trial of telehealth interventions designed to reduce the incidence of secondary conditions among people with mobility impairment resulting from spinal cord injury (SCI).

Methods.

Patients with spinal cord injuries were recruited during their initial stay at a rehabilitation facility in Atlanta, They received a video-based intervention for nine weeks, a telephone-based intervention for nine weeks, or standard follow-up care. Participants are followed for at least one year, to monitor days of hospitalization, depressive symptoms, and health-related quality of life.

Results.

Health-related quality of life was measured using the Quality of Well-Being (QWB) scale. QWB scores (n = 111) did not differ significantly between the three intervention groups at the end of the intervention period. At year one post discharge, however, scores for those completing one year of enrollment (n = 47) were significantly higher for the intervention groups compared to standard care. Mean annual hospital days were 3.00 for the video group, 5.22 for the telephone group, and 7.95 for the standard care group.

Conclusions.

Preliminary evidence suggests that in-home telephone or video-based interventions do improve health-related outcomes for newly injured SCI patients. Telehealth interventions may be cost-saving if program costs are more than offset by a reduction in rehospitalization costs, but differential advantages of video-based interventions versus telephone alone warrant further examination.
Discrete point symmetries of ordinary differential equations
Authors: Hydon P. E.
Published: July 2002

This paper describes a method that enables the user to construct systematically the set of all discrete point symmetries of a given ordinary differential equation (ODE) of order two or greater, provided that the ODE has at least a one–parameter Lie group of point symmetries. The method is easy to use, and is based upon Li's method of constructing continuous symmetries. The calculations are simple, and computer algebra is not usually required. Various examples are used to illustrate the method. The paper concludes with a proof that every ODE whose Lie group of point symmetries is isomorphic to the unimodular group has at least four inequivalent real discrete point symmetries.
Roles of Na
+
–Ca
2+
exchange and of mitochondria in the regulation of presynaptic Ca
2+
and spontaneous glutamate release
Authors: Scotti Alessandra L. , Chatton Jean–Yves , Reuter Harald
Published: July 2002

The release of neurotransmitter from presynaptic terminals depends on an increase in the intracellular Ca
2+
concentration ([Ca
2+
]
i
). In addition to the opening of presynaptic Ca
2+
channels during excitation, other Ca
2+
transport systems may be involved in changes in [Ca
2+
]
i
.We have studied the regulation of[Ca
2+
]
i
in nerve terminals of hippocampal cells in culture by the Na
+
–Ca
2+
exchanger and by mitochondria. In addition, we have measured changes in the frequency of spontaneous excitatory postsynaptic currents (sEPSC) before and after the inhibition of the exchanger and of mitochondrial metabolism. We found rather heterogeneous [Ca
2+
]
i
responses of individual presynaptic terminals after inhibition of Na
+
–Ca
2+
exchange. The increase in [Ca
2+
]
i
became more uniform and much larger after additional treatment of the cells with mitochondrial inhibitors. Correspondingly, sEPSC frequencies changed very little when only Na
+
–Ca
2+
exchange was inhibited, but increased dramatically after additional inhibition of mitochondria. Our results provide evidence for prominent roles of Na
+
Ca
2+
exchange and mitochondria in presynaptic Ca
2+
regulation and spontaneous glutamate release.
Splendours and miseries of the brain
Authors: Zeki S.
Published: July 2002

In this speculative essay, I examine two evolutionary developments underlying the enormous success of the human brain: its capacity to acquire knowledge and its variability across individuals. A feature of an efficient knowledge–acquiring system is, I believe, its capacity to abstract and to formulate ideals. Both attributes carry with them a clash between experience of the particular and what the brain has developed from experience of the many. Both therefore can lead to much disappointment in our daily lives. This disappointment is heightened by the fact that both abstraction and ideals are subject to variability in time within an individual and between individuals. Variability, which is a cherished source for evolutionary selection, can also be an isolating and individualizing feature in society. Thus the very features of the human brain which underlie our enormous evolutionary success can also be a major source of our misery.
Elastomeric gradients: a hedge against stress concentration in marine holdfasts?
Authors: Waite J. H. , Vaccaro E. , Sun C. , Lucas J. M.
Published: July 2002

The byssal threads of marine mussels are elastomeric fibres with a great capacity for absorbing and dissipating energy. Up to 70% of the total absorbed energy can be dissipated in the byssus. Because byssal threads attach the mussel to hard inert surfaces in its habitat, they must combine the need to be good shock absorbers with appropriate matching of Young's modulus between living tissue and a hard sub–stratum such as stone—stiffnesses that can differ by five orders of magnitude. Recent data suggest that improved modulus matching and decreased stress concentration between different portions of the byssus is achieved by the use of protein gradients. Protein gradients in byssal threads are constructed using natural macromolecular chimeras having a central collagenous domain, variable flanking modules and histidine–rich amino and carboxy termini. Stiff silk–like flanking modules prevail distally, while at the animal end, rubbery modules resembling elastin predominate. In between the two thread ends there is a mix of both module types. The histidine–rich termini provide metal binding/cross–linking sites, while collagen domains may confer self–assembly on all parts of the structure. A graded axial distribution of flanking modules is expected to moderate stress concentration in joined materials having disparate moduli.
D box and KEN box motifs in budding yeast Hsl1p are required for APC-mediated degradation and direct binding to Cdc20p and Cdh1p
Authors: Burton Janet L. , Solomon Mark J.
Published: July 2002

The precise order of molecular events during cell cycle progression depends upon ubiquitin-mediated proteolysis of cell cycle regulators. We demonstrated previously that Hsl1p, a protein kinase that inhibits the Swe1p protein kinase in a bud morphogenesis checkpoint, is targeted for ubiquitin-mediated turnover by the anaphase-promoting complex (APC). Here, we investigate regions of Hsl1p that are critical both for binding to the APC machinery and for APC-mediated degradation. We demonstrate that Hsl1p contains both a destruction box (D box) and a KEN box motif that are necessary for Hsl1p turnover with either APCCdc20 or APCCdh1. In coimmunoprecipitation studies, the D box of full-length Hsl1p was critical for association with Cdc20p, whereas the KEN box was important for association with Cdh1p. Fusion of a 206-amino-acid fragment of Hsl1p containing these motifs to a heterologous protein resulted in APC-dependent degradation of the fusion protein that required intact D box and KEN box motifs. Finally, this bacterially expressed Hsl1p fusion protein interacted with Cdc20p and Cdh1p either translated in vitro or expressed in and purified from insect cells. Binding to Cdc20p and Cdh1p was disrupted completely by a D box/KEN box double mutant. These results indicate that D box and KEN box motifs are important for direct binding to the APC machinery, leading to ubiquitination and subsequent protein degradation.
Structure and stability effects of mutations designed to increase the primary sequence symmetry within the core region of a β‐trefoil
Authors: Brych Stephen R. , Blaber Sachiko I. , Logan Timothy M. , Blaber Michael
Published: July 2002

Human acidic fibroblast growth factor (FGF‐1) is a member of the β‐trefoil hyperfamily and exhibits a characteristic threefold symmetry of the tertiary structure. However, evidence of this symmetry is not readily apparent at the level of the primary sequence. This suggests that while selective pressures may exist to retain (or converge upon) a symmetric tertiary structure, other selective pressures have resulted in divergence of the primary sequence during evolution. Using intra‐chain and homologue sequence comparisons for 19 members of this family of proteins, we have designed mutants of FGF‐1 that constrain a subset of core‐packing residues to threefold symmetry at the level of the primary sequence. The consequences of these mutations regarding structure and stability were evaluated using a combination of X‐ray crystallography and differential scanning calorimetry. The mutational effects on structure and stability can be rationalized through the characterization of “microcavities” within the core detected using a 1.0Å probe radius. The results show that the symmetric constraint within the primary sequence is compatible with a well‐packed core and near wild‐type stability. However, despite the general maintenance of overall thermal stability, a noticeable increase in non‐two‐state denaturation follows the increase in primary sequence symmetry. Therefore, properties of folding, rather than stability, may contribute to the selective pressure for asymmetric primary core sequences within symmetric protein architectures.
A conducting plastic simulating brain tissue
Authors: Burmeister Jay , Kota Chandrasekhar , Maughan Richard L. , Spokas John J. , Coderre Jeffrey A. , Ma Ruimei , Wielopolski Lucian
Published: July 2002

A new conducting plastic has been composed which accurately simulates the photon and neutron absorption properties of brain tissue. This tissue‐equivalent (TE) plastic was formulated to match the hydrogen and nitrogen constituents recommended by ICRU Report #44 for brain tissue. Its development was initiated by the inability of muscle tissue‐equivalent plastic to closely approximate brain tissue with respect to low‐energy neutron interactions. This new plastic is particularly useful as an electrode in TE dosimetry devices for boron neutron capture therapy (BNCT), which utilizes low‐energy neutrons for radiotherapy of the brain. Absorbed dose measurements in a clinical BNCT beam using a proportional counter constructed from this TE plastic show good agreement with Monte Carlo calculations.
Artificial neural network Radon inversion for image reconstruction
Authors: Rodriguez Alberto F. , Blass William E. , Missimer John H. , Leenders Klaus L.
Published: July 2002

Image reconstruction techniques are essential to computer tomography. Algorithms such as filtered backprojection (FBP) or algebraic techniques are most frequently used. This paper presents an attempt to apply a feed‐forward back‐propagation supervised artificial neural network (BPN) to tomographic image reconstruction, specifically to positron emission tomography (PET). The main result is that the network trained with Gaussian test images proved to be successful at reconstructing images from projection sets derived from arbitrary objects. Additional results relate to the design of the network and the full width at half maximum (FWHM) of the Gaussians in the training sets. First, the optimal number of nodes in the middle layer is about an order of magnitude less than the number of input or output nodes. Second, the number of iterations required to achieve a required training set tolerance appeared to decrease exponentially with the number of nodes in the middle layer. Finally, for training sets containing Gaussians of a single width, the optimal accuracy of reconstructing the control set is obtained with a FWHM of three pixels. Intended to explore feasibility, the BPN presented in the following does not provide reconstruction accuracy adequate for immediate application to PET. However, the trained network does reconstruct general images independent of the data with which it was trained. Proposed in the concluding section are several possible refinements that should permit the development of a network capable of fast reconstruction of three‐dimensional images from the discrete, noisy projection data characteristic of PET.
The x‐ray sensitivity of amorphous selenium for mammography
Authors: Stone Mary F. , Zhao Wei , Jacak Barbara V. , O'Connor Paul , Yu Bo , Rehak Pavel
Published: July 2002

A study of the x‐ray sensitivity of amorphous selenium (a‐Se) for digital mammography has been performed. A uniform layer of a‐Se was deposited on a glass substrate with electrodes on both surfaces. The deposition procedure was identical to that used for a‐Se flat‐panel detectors. A high voltage was applied to the top surface of the a‐Se layer in order to establish an electric field Then the sample was exposed to x rays with 27 kVp spectra generated from an x‐ray tube with a molybdenum (Mo) target. The mean x‐ray energy of the spectrum used was ∼16.6 keV. The x‐ray current generated by the a‐Se layer was measured as a function of From the current measurement and the estimation of total x‐ray energy absorbed in the a‐Se, the energy required to create one electron‐hole pair (EHP), W, was determined as a function of It was found that at the most commonly used of 10 V/μm, W was measured as 64 eV. This is considerably higher than the widely accepted typical value of measured at higher x‐ray photon energies (e.g., 50 keV). The dependence of W as a function of can be best fitted using the empirical expression of This relationship is consistent with the results obtained at higher x‐ray energies. This article provides an accurate measurement of x‐ray sensitivity of a‐Se at mammographic energies independent of detector operation, such as the most recently developed flat‐panel detectors. The results will be a useful tool for investigation and optimization of a‐Se‐based x‐ray imaging detectors, such as determination of pixel fill‐factor and optimal during operation.
One model for an integrated math/physics course focusing on electricity and magnetism and related calculus topics
Authors: Dunn Jason W. , Barbanel Julius
Published: July 2002

Over the last decade, there has been an increasing, widespread pedagogical interest in developing various types of integrated curricula for science and engineering programs. Over the last three years, a year-long Integrated Math/Physics course has been developed at Union College. This paper will focus on a model for a one-quarter integrated course organized around a traditional set of electricity and magnetism (E&M) physics topics, integrated with appropriate mathematical topics. Traditional, nonintegrated E&M physics students often struggle with challenging vector calculus ideas which may have been forgotten, not yet encountered, or introduced with different notation in different contexts. Likewise, traditional vector calculus mathematics students are often unable to gain intuitive insight, or fail to grasp the physical significance of many of the vector calculus ideas they are learning. Many of these frustrations are due to the fact that at many schools, the physics and calculus teachers teaching separate courses probably have little or no idea what their fellow educators are actually doing in these courses. Substantial differences in context, notation, and philosophy can cause breakdowns in the transfer of knowledge between mathematics and physics courses. We will discuss the methods, philosophy, and implementation of our course, and then go on to present what we feel were the substantial strengths and insights gained from a thoughtful integration of the two subjects. In addition, some problem areas and recommendations for probable student difficulties will be addressed.
Dynamics of gas bubbles in viscoelastic fluids. II. Nonlinear viscoelasticity
Authors: Allen John S. , Roy Ronald A.
Published: July 2002

The nonlinear oscillations of a spherical, acoustically forced gas bubble in nonlinear viscoelastic media are examined. The constitutive equation [Upper-Convective Maxwell (UCM)] used for the fluid is suitable for study of large-amplitude excursions of the bubble, in contrast to the previous work of the authors which focused on the smaller amplitude oscillations within a linear viscoelastic fluid [J. S. Allen and R. A. Roy, J. Acoust. Soc. Am. 107, 3167–3178 (2000)]. Assumptions concerning the trace of the stress tensor are addressed in light of the incorporation of viscoelastic constitutive equations into bubble dynamics equations. The numerical method used to solve the governing system of equations (one integrodifferential equation and two partial differential equations) is outlined. An energy balance relation is used to monitor the accuracy of the calculations and the formulation is compared with the previously developed linear viscoelastic model. Results are found to agree in the limit of small deformations; however, significant divergence for larger radial oscillations is noted. Furthermore, the inherent limitations of the linear viscoelastic approach are explored in light of the more complete nonlinear formulation. The relevance and importance of this approach to biomedical ultrasound applications are highlighted. Preliminary results indicate that tissue viscoelasticity may be an important consideration for the risk assessment of potential cavitation bioeffects.
Kramers–Kronig relations applied to finite bandwidth data from suspensions of encapsulated microbubbles
Authors: Mobley Joel , Waters Kendall R. , Hughes Michael S. , Hall Christopher S. , Marsh Jon N. , Brandenburger Gary H. , Miller James G.
Published: July 2002

In this work, the Kramers–Kronig (K–K) relations are applied to experimental data of resonant nature by limiting the interval of integration to the measurement spectrum. The data are from suspensions of encapsulated microbubbles (Albunex®) and have the characteristics of an ultrasonic notch filter. The goal is to test the consistency of this dispersion and attenuation data with the Kramers–Kronig relations in a strict manner, without any parameters from outside the experimental bandwidth entering in to the calculations. In the course of reaching the goal, the artifacts associated with the truncation of the integrals are identified and it is shown how their impacts on the results can be minimized. The problem is first approached analytically by performing the Kramers–Kronig calculations over a restricted spectral band on a specific Hilbert transform pair (Lorentzian curves). The resulting closed-form solutions illustrate the type of artifacts that can occur due to truncation and also show that accurate results can be achieved. Next, both twice-subtracted and lower-order Kramers–Kronig relations are applied directly to the attenuation and dispersion data from the encapsulated microbubbles. Only parameters from within the experimental attenuation coefficient and phase velocity data sets are used. The twice-subtracted K–K relations produced accurate estimates for both the attenuation coefficient and dispersion across all 12 data sets. Lower-order Kramers–Kronig relations also produced good results over the finite spectrum for most of the data. In 2 of the 12 cases, the twice-subtracted relations tracked the data markedly better than the lower-order predictions. These calculations demonstrate that truncation artifacts do not overwhelm the causal link between the phase velocity and the attenuation coefficient for finite bandwidth calculations. This work provides experimental evidence supporting the validity of the subtracted forms of the acoustic K–K relations between the phase velocity and attenuation coefficient.
Three-dimensional sound localization from a compact non-coplanar array of microphones using tree-based learning
Authors: Weng Juyang , Guentchev Kamen Y.
Published: July 2002

One of the various human sensory capabilities is to identify the direction of perceived sounds. The goal of this work is to study sound source localization in three dimensions using some of the most important cues the human uses. In an attempt to satisfy the requirements of portability and miniaturization in robotics, this approach employs a compact sensor structure that can be placed on a mobile platform. The objective is to estimate the relative sound source position in three-dimensional space without imposing excessive restrictions on its spatio-temporal characteristics and the environment structure. Two types of features are considered, interaural time and level differences. Their relative effectiveness for localization is studied, as well as a practical way of using these complementary parameters. A two-stage procedure was used. In the training stage, sound samples are produced from points with known coordinates and then are stored. In the recognition stage, unknown sounds are processed by the trained system to estimate the 3D location of the sound source. Results from the experiments showed under ±3° in average angular error and less than ±20% in average radial distance error.
Effects of a limited class of nonlinearities on estimates of relative weights
Authors: Richards Virginia M.
Published: July 2002

Perturbation analyses have been applied in recent years to determine the relative contribution of individual stimulus components in detection and discrimination tasks. Responses to stimulus samples are compared to stimulus parameters to determine the details of the decision rule. Often, a linear model is assumed and it is of interest to determine the relative contribution of different stimulus elements to the decision. Here, biases in estimated relative weights are considered for the case where the decision variable is given by D=(∑(αiXin)k)m and the stimulus components, the Xi, are normally distributed, of equal variance, and mutually independent. The αi are the “true” combination weights, and n, k, and m are positive reals. The method used to estimate relative weights is the correlation coefficient between the Xi and the observer’s responses. Estimates of relative αi do not depend on m but may depend on the mean values of the Xi and the values of n and k (a dependence on the variance, σi2, holds even for linear transformations).
Assessing auditory distance perception using virtual acoustics
Authors: Zahorik Pavel
Published: July 2002

In most naturally occurring situations, multiple acoustic properties of the sound reaching a listener’s ears change as sound source distance changes. Because many of these acoustic properties, or cues, can be confounded with variation in the acoustic properties of the source and the environment, the perceptual processes subserving distance localization likely combine and weight multiple cues in order to produce stable estimates of sound source distance. Here, this cue-weighting process is examined psychophysically, using a method of virtual acoustics that allows precise measurement and control of the acoustic cues thought to be salient for distance perception in a representative large-room environment. Though listeners’ judgments of sound source distance are found to consistently and exponentially underestimate true distance, the perceptual weight assigned to two primary distance cues (intensity and direct-to-reverberant energy ratio) varies substantially as a function of both sound source type (noise and speech) and angular position (0° and 90° relative to the median plane). These results suggest that the cue-weighting process is flexible, and able to adapt to individual distance cues that vary as a result of source properties and environmental conditions.
Knowledge about typical source output influences perceived auditory distance
Authors: Philbeck John W. , Mershon Donald H.
Published: July 2002

Vocal effort is known to influence the judged distance of speech sound sources. The present research examined whether this influence is due to long-term experience gained prior to the experiment versus short-term experience gained from exposure to speech stimuli earlier in the same experiment. Speech recordings were presented to 192 blindfolded listeners at three levels of vocal output. Even upon the first presentation, shouting voices were reported as appearing farthest, whispered voices closest. This suggests that auditory distance perception can be affected by past experience in a way that does not require explicit comparisons between individual stimuli.
Temporary shift in masked hearing thresholds in odontocetes after exposure to single underwater impulses from a seismic watergun
Authors: Finneran James J. , Schlundt Carolyn E. , Dear Randall , Carder Donald A. , Ridgway Sam H.
Published: July 2002

A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and a white whale (Delphinapterus leucas) before and after exposure to single underwater impulsive sounds produced from a seismic watergun. Pre- and postexposure thresholds were compared to determine if a temporary shift in masked hearing thresholds (MTTS), defined as a 6-dB or larger increase in postexposure thresholds, occurred. Hearing thresholds were measured at 0.4, 4, and 30 kHz. MTTSs of 7 and 6 dB were observed in the white whale at 0.4 and 30 kHz, respectively, approximately 2 min following exposure to single impulses with peak pressures of 160 kPa, peak-to-peak pressures of 226 dB re 1 μPa, and total energy fluxes of 186 dB re 1 μPa2⋅s. Thresholds returned to within 2 dB of the preexposure value approximately 4 min after exposure. No MTTS was observed in the dolphin at the highest exposure conditions: 207 kPa peak pressure, 228 dB re 1 μPa peak-to-peak pressure, and 188 dB re 1 μPa2⋅s total energy flux.
Glottal characteristics of female speakers: Acoustic correlates
Authors: Hanson Helen M.
Published: July 2002

The aim of the research reported in this paper is to formulate a set of acoustic parameters of the voicing source that reflect individual differences in the voice qualities of female speakers. Theoretical analysis and observations of experimental data suggest that a more open glottal configuration results in a glottal volume-velocity waveform with relatively greater low-frequency and weaker high-frequency components, compared to a waveform produced with a more adducted glottal configuration. The more open glottal configuration also leads to a greater source of aspiration noise and larger bandwidths of the natural frequencies of the vocal tract, particularly the first formant. These different attributes of the glottal waveform can be measured directly from the speech spectrum or waveform. A set of acoustic parameters that are likely to indicate glottal characteristics is described. These parameters are measured in the speech of a group of female speakers, and the glottal configurations of the speakers are hypothesized. This research contributes to the description of normal variations of voicing characteristics across speakers and to a continuing effort to improve the analysis and synthesis of female speech. It may also have applications in clinical settings.