bluuebunny/crossref_metadata_2025 huggingface dataset:
Simplicity and the stable rank of some free product C*-algebras
Authors: Dykema Kenneth
Published: July 2002

A necessary and sufficient condition for the simplicity of the C

∗

^{*}

–algebra reduced free product of finite dimensional abelian algebras is found, and it is proved that the stable rank of every such free product is 1. Related results about other reduced free products of C

∗

^{*}

–algebras are proved.
Computing the canonical height on K3 surfaces
Authors: Call Gregory , Silverman Joseph
Published: July 2002

Let

S
S

be a surface in

P

2

×

P

2

\mathbb {P}^2\times \mathbb {P}^2

given by the intersection of a (1,1)-form and a (2,2)-form. Then

S
S

is a K3 surface with two noncommuting involutions

σ
x

\sigma ^x

and

σ
y

\sigma ^y

. In 1991 the second author constructed two height functions

h
^

+

\hat {h}^+

and

h
^

−

\hat {h}^-

which behave canonically with respect to

σ
x

\sigma ^x

and

σ
y

\sigma ^y

, and in 1993 together with the first author showed in general how to decompose such canonical heights into a sum of local heights

∑
v

λ
^

±

(

⋅

,
v
)

\sum _v \hat {\lambda }^\pm (\,\cdot \,,v)

. We discuss how the geometry of the surface

S
S

is related to formulas for the local heights, and we give practical algorithms for computing the involutions

σ
x

\sigma ^x

,

σ
y

\sigma ^y

, the local heights

λ
^

+

(

⋅

,
v
)

\hat {\lambda }^+(\,\cdot \,,v)

,

λ
^

−

(

⋅

,
v
)

\hat {\lambda }^-(\,\cdot \,,v)

, and the canonical heights

h
^

+

\hat {h}^+

,

h
^

−

\hat {h}^-

.
Convergence rate of approximate solutions to weakly coupled nonlinear systems
Authors: Nessyahu Haim
Published: July 2002

We study the convergence rate of approximate solutions to nonlinear hyperbolic systems which are weakly coupled through linear source terms. Such weakly coupled

2
×
2

2 \times 2

systems appear, for example, in the context of resonant waves in gas dynamics equations. This work is an extension of our previous scalar analysis. This analysis asserts that a One Sided Lipschitz Condition (OSLC, or

L
i
p

+

\mathrm {Lip}^+

-stability) together with

W

−
1
,
1

W^{-1,1}

-consistency imply convergence to the unique entropy solution. Moreover, it provides sharp convergence rate estimates, both global (quantified in terms of the

W

s
,
p

W^{s,p}

-norms) and local. We focus our attention on the

L
i
p

+

\mathrm {Lip}^+

-stability of the viscosity regularization associated with such weakly coupled systems. We derive sufficient conditions, interesting for their own sake, under which the viscosity (and hence the entropy) solutions are

L
i
p

+

\mathrm {Lip}^+

-stable in an appropriate sense. Equipped with this, we may apply the abovementioned convergence rate analysis to approximate solutions that share this type of

L
i
p

+

\mathrm {Lip}^+

-stability.
Stieltjes polynomials and related quadrature formulae for a class of weight functions
Authors: Gautschi Walter , Notaris Sotirios
Published: July 2002

Consider a (nonnegative) measure

d
σ

d \sigma

with support in the interval

[
a
,
b
]

[a,b]

such that the respective orthogonal polynomials, above a specific index

ℓ
\ell

, satisfy a three-term recurrence relation with constant coefficients. We show that the corresponding Stieltjes polynomials, above the index

2
ℓ
−
1

2\ell -1

, have a very simple and useful representation in terms of the orthogonal polynomials. As a result of this, the Gauss-Kronrod quadrature formulae for

d
σ

d \sigma

have all the desirable properties, namely, the interlacing of nodes, their inclusion in the closed interval

[
a
,
b
]

[a,b]

(under an additional assumption on

d
σ

d \sigma

), and the positivity of all weights. Furthermore, the interpolatory quadrature formulae based on the zeros of the Stieltjes polynomials have positive weights, and both of these quadrature formulae have elevated degrees of exactness.
Nonlinear stability of stationary discrete shocks for nonconvex scalar conservation laws
Authors: Liu Hailiang , Wang Jinghua
Published: July 2002

This paper is to study the asymptotic stability of stationary discrete shocks for the Lax-Friedrichs scheme approximating nonconvex scalar conservation laws, provided that the summations of the initial perturbations equal to zero. The result is proved by using a weighted energy method based on the nonconvexity. Moreover, the

l
1

l^1

stability is also obtained. The key points of our proofs are to choose a suitable weight function.
A priori error estimates for numerical methods for scalar conservation laws. Part II : flux-splitting monotone schemes on irregular Cartesian grids
Authors: Cockburn Bernardo , Gremaud Pierre-Alain
Published: July 2002

This paper is the second of a series in which a general theory of a priori error estimates for scalar conservation laws is constructed. In this paper, we focus on how the lack of consistency introduced by the nonuniformity of the grids influences the convergence of flux-splitting monotone schemes to the entropy solution. We obtain the optimal rate of convergence of

(
Δ
x

)

1

/

2

(\Delta x)^{1/2}

in

L

∞

(

L

1

)

L^{\infty }(L^{1})

for consistent schemes in arbitrary grids without the use of any regularity property of the approximate solution. We then extend this result to less consistent schemes, called

p
−

p-

consistent schemes, and prove that they converge to the entropy solution with the rate of

(
Δ
x

)

min
{
1

/

2
,
p
}

(\Delta x)^{\min \{1/2,p\}}

in

L

∞

(

L

1

)

L^{\infty }(L^{1})

; again, no regularity property of the approximate solution is used. Finally, we propose a new explanation of the fact that even inconsistent schemes converge with the rate of

(
Δ
x

)

1

/

2

(\Delta x)^{1/2}

in

L

∞

(

L

1

)

L^{\infty }(L^{1})

. We show that this well-known supraconvergence phenomenon takes place because the consistency of the numerical flux and the fact that the scheme is written in conservation form allows the regularity properties of its approximate solution (total variation boundedness) to compensate for its lack of consistency; the nonlinear nature of the problem does not play any role in this mechanism. All the above results hold in the multidimensional case, provided the grids are Cartesian products of one-dimensional nonuniform grids.
Double roots of [-1,1] power series and related matters
Authors: Pinner Christopher
Published: July 2002

For a given collection of distinct arguments

θ
→

=
(

θ

1

,
…
,

θ

t

)

\vec {\theta }=(\theta _{1},\ldots ,\theta _{t})

, multiplicities

k
→

=
(

k

1

,
…
,

k

t

)
,

\vec {k}=(k_{1},\ldots ,k_{t}),

and a real interval

I
=
[
U
,
V
]

I=[U,V]

containing zero, we are interested in determining the smallest

r
r

for which there is a power series

f
(
x
)
=
1
+

∑

n
=
1

∞

a

n

x

n

f(x)=1+\sum _{n=1}^{\infty } a_{n}x^{n}

with coefficients

a

n

a_{n}

in

I
I

, and roots

α

1

=
r

e

2
π
i

θ

1

,
…
,

α

t

=
r

e

2
π
i

θ

t

\alpha _{1}=re^{2\pi i\theta _{1}}, \ldots ,\alpha _{t}=re^{2\pi i\theta _{t}}

of order

k

1

,
…
,

k

t

k_{1},\ldots ,k_{t}

respectively. We denote this by

r
(

θ
→

,

k
→

;
I
)

r(\vec {\theta },\vec {k};I)

. We describe the usual form of the extremal series (we give a sufficient condition which is also necessary when the extremal series possesses at least

(

∑

i
=
1

t

δ
(

θ

i

)

k

i

)

−
1

\left (\sum _{i=1}^{t} \delta (\theta _{i})k_{i}\right ) -1

non-dependent coefficients strictly inside

I
I

, where

δ
(

θ

i

)

\delta (\theta _{i})

is 1 or 2 as

α

i

\alpha _{i}

is real or complex). We focus particularly on

r
(
θ
,
2
;
[
−
1
,
1
]
)

r(\theta ,2;[-1,1])

, the size of the smallest double root of a

[
−
1
,
1
]

[-1,1]

power series lying on a given ray (of interest in connection with the complex analogue of work of Boris Solomyak on the distribution of the random series

∑
±

λ

n

\sum \pm \lambda ^{n}

). We computed the value of

r
(
θ
,
2
;
[
−
1
,
1
]
)

r(\theta ,2; [-1,1])

for the rationals

θ
\theta

in

(
0
,
1

/

2
)

(0,1/2)

of denominator less than fifty. The smallest value we encountered was

r
(
4

/

29
,
2
;
[
−
1
,
1
]
)
=
0.7536065594...

r(4/29,2;[-1,1])=0.7536065594...

. For the one-sided intervals

I
=
[
0
,
1
]

I=[0,1]

and

[
−
1
,
0
]

[-1,0]

the corresponding smallest values were

r
(
11

/

30
,
2
;
[
0
,
1
]
)
=
.8237251991
.
.
.

r(11/30,2;[0,1])=.8237251991...

and

r
(
1

/

3
,
2
;
[
−
1
,
0
]
)
=
.8656332072
.
.
.

r(1/3,2;[-1,0])=.8656332072...

.
Tau method approximation of a generalized Epstein-Hubbell elliptic-type integral
Authors: Khajah H.
Published: July 2002

We consider the evaluation of a recent generalization of the Ep- stein-Hubbell elliptic-type integral using the tau method approximation with a Chebyshev polynomial basis. This also leads to an approximation of Lauricella’s hypergeometric function of three variables. Numerical results are given for polynomial approximations of degree 6.
Alterations can remove singularities
Authors: Oort Frans
Published: July 2002

This note is a review of: A. J. de Jong - Smoothness, semi-stability and alterations. Manuscript 1995, 39 pp.: Publications Mathématiques I.H.E.S. 83, 1996, pp. 51-93.
Integral transforms with exponential kernels and Laplace transform
Authors: Kashiwara Masaki , Schapira Pierre
Published: July 2002

Let

X

⟵
f

Z

⟶
g

Y

X \underset {f}{\longleftarrow } Z \underset {g}{\longrightarrow } Y

be a correspondence of complex manifolds. We study integral transforms associated to kernels

exp
⁡
(
φ
)

\exp (\varphi )

, with

φ
\varphi

meromorphic on

Z
Z

, acting on formal or moderate cohomologies. Our main application is the Laplace transform. In this case,

X
X

is the projective compactification of the vector space

V
≃

C

n

V \simeq \mathbb {C}^n

,

Y
Y

is its dual space,

Z
=
X
×
Y

Z=X\times Y

and

φ
(
z
,
w
)
=
⟨
z
,
w
⟩

\varphi (z,w) =\langle z,w \rangle

. We obtain the isomorphisms:
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartLayout 1st Row 1st Column Blank 2nd Column a m p semicolon upper F circled-times Superscript upper W Baseline script upper O Subscript upper V Baseline asymptotically-equals upper F Superscript logical-and Baseline left-bracket n right-bracket circled-times Superscript upper W Baseline script upper O Subscript upper V Sub Superscript asterisk Subscript Baseline comma upper T upper H o m left-parenthesis upper F comma script upper O Subscript upper V Baseline right-parenthesis asymptotically-equals upper T upper H o m left-parenthesis upper F Superscript logical-and Baseline left-bracket n right-bracket comma script upper O Subscript upper V Sub Superscript asterisk Subscript Baseline right-parenthesis EndLayout">

a
m
p
;
F

⊗
W

O

V

≃

F
∧

[
n
]

⊗
W

O

V
∗

,

THom
⁡
(
F
,

O

V

)
≃
THom
⁡
(

F
∧

[
n
]
,

O

V
∗

)

\begin{align*} &F \otimes ^W \mathcal {O}_V \simeq F^\wedge [n] \otimes ^W \mathcal {O}_{V^*},\quad \operatorname {THom}(F,\mathcal {O}_V) \simeq \operatorname {THom}(F^\wedge [n],\mathcal {O}_{V^*}) \end{align*}

where

F
F

is a conic and

R

\mathbb {R}

-constructible sheaf on

V
V

and

F
∧

F^\wedge

is its Fourier-Sato transform. Some applications are discussed.
Classification of admissible nilpotent orbits in simple real Lie algebras 𝐸₆₍₆₎ and 𝐸₆₍₋₂₆₎
Authors: Noël Alfred
Published: July 2002

This paper completes the classification of admissible nilpotent orbits of the noncompact simple exceptional real Lie algebras. The author has previoulsly determined such orbits for exceptional real simple Lie algebras of inner type. Here he uses the same techniques, with some modifications, to classify the admissible nilpotent orbits of

E

6
(
6
)

E_{6(6)}

and

E

6
(
−
26
)

E_{6(-26)}

under their simply connected Lie groups.
Analytic families of eigenfunctions on a reductive symmetric space
Authors: van den Ban E. , Schlichtkrull H.
Published: July 2002

Let

X
=
G

/

H

X=G/H

be a reductive symmetric space, and let

D

(
X
)

\mathbb D(X)

denote the algebra of

G
G

-invariant differential operators on

X
X

. The asymptotic behavior of certain families

f
λ

f_\lambda

of generalized eigenfunctions for

D

(
X
)

\mathbb D(X)

is studied. The family parameter

λ
\lambda

is a complex character on the split component of a parabolic subgroup. It is shown that the family is uniquely determined by the coefficient of a particular exponent in the expansion. This property is used to obtain a method by means of which linear relations among partial Eisenstein integrals can be deduced from similar relations on parabolic subgroups. In the special case of a semisimple Lie group considered as a symmetric space, this result is closely related to a lifting principle introduced by Casselman. The induction of relations will be applied in forthcoming work on the Plancherel and the Paley-Wiener theorem.
The Teichmüller distance on the space of flat conformal structures
Authors: Izeki Hiroyasu
Published: July 2002

We define the Teichmüller pseudodistance on spaces of flat conformal structures by the same manner as classical Teichmüller distance on the Teichmüller space of Riemann surfaces. We will prove that for compact manifolds this pseudodistance becomes a complete distance. We will also prove similar results for noncompact manifolds under certain assumptions.
Conformally converting cusps to cones
Authors: Judge Christopher
Published: July 2002

Conformal deformations of hyperbolic surfaces with conical singularities are shown to be real-analytic. The first nontrivial term in the power series expansion around a cusped surface is shown to be a multiple of the Eisenstein series

E
2

E_2

.
Volume formulae for regular hyperbolic cubes
Authors: Marshall T.
Published: July 2002

We express the volume of a regular cube in hyperbolic

n
n

-space as an integral on

[
0
,
∞
)

[0, \infty )

, and derive from this an asymptotic volume formula for the regular ideal hyperbolic

n
n

-cube. This in turn is applied to finding an asymptotic lower bound for the least number of simplices into which a Euclidean

n
n

-cube can be triangulated.
The 14-kDa Dynein Light Chain-Family Protein Dlc1 Is Required for Regular Oscillatory Nuclear Movement and Efficient Recombination during Meiotic Prophase in Fission Yeast
Authors: Miki Futaba , Okazaki Koei , Shimanuki Mizuki , Yamamoto Ayumu , Hiraoka Yasushi , Niwa Osami
Published: July 2002

A Schizosaccharomyces pombe spindle pole body (SPB) protein interacts in a two-hybrid system with Dlc1, which belongs to the 14-kDa Tctex-1 dynein light chain family. Green fluorescent protein-tagged Dlc1 accumulated at the SPB throughout the life cycle. During meiotic prophase, Dlc1 was present along astral microtubules and microtubule-anchoring sites on the cell cortex, reminiscent of the cytoplasmic dynein heavy chain Dhc1. In a dlc1-null mutant, Dhc1-dependent nuclear movement in meiotic prophase became irregular in its duration and direction. Dhc1 protein was displaced from the cortex anchors and the formation of microtubule bundle(s) that guide nuclear movement was impaired in the mutant. Meiotic recombination in the dlc1 mutant was reduced to levels similar to that in the dhc1 mutant. Dlc1 and Dhc1 also have roles in karyogamy and rDNA relocation during the sexual phase. Strains mutated in both the dlc1 and dhc1loci displayed more severe defects in recombination, karyogamy, and sporulation than in either single mutant alone, suggesting that Dlc1 is involved in nuclear events that are independent of Dhc1. S. pombe contains a homolog of the 8-kDa dynein light chain, Dlc2. This class of dynein light chain, however, is not essential in either the vegetative or sexual phases.
PALI: a database of alignments and phylogeny of homologous

protein structures
Authors: Sujatha S. , Balaji S. , Srinivasan N.
Published: July 2002

Summary: PALI is a database of structure-based sequence alignments and phylogenetic relationships derived on the basis of three-dimensional structures of homologous proteins. This database enables grouping of pairs of homologous protein structures on the basis of their sequence identity calculated from the structure-based alignment and PALI also enables association of a new sequence to a family and automatic generation of a dendrogram combining the query sequence and homologous protein structures.

Availability: PALI can be accessed on the web at: http://pauling.mbu.iisc.ernet.in/~pali

Contact: ns@mbu.iisc.ernet.in

* To whom correspondence should be addressed.
Phytochromes and photomorphogenesis in
Arabidopsis
Authors: Whitelam Garry C. , Patel Samita , Devlin Paul F.
Published: July 2002

Plants have evolved exquisite sensory systems for monitoring their light environment. The intensity, quality, direction and duration of light are continuously monitored by the plant and the information gained is used to modulate all aspects of plant development. Several classes of distinct photoreceptors, sensitive to different regions of the light spectrum, mediate the developmental responses of plants to light signals. The red–far–red light–absorbing, reversibly photochromic phytochromes are perhaps the best characterized of these. Higher plants possess a family of phytochromes, the apoproteins of which are encoded by a small, divergent gene family.
Arabidopsis
has five apophytochrome–encoding genes,
PHYA–PHYE
. Different phytochromes have discrete biochemical and physiological properties, are differentially expressed and are involved in the perception of different light signals. Photoreceptor and signal transduction mutants of
Arabidopsis
are proving to be valuable tools in the molecular dissection of photomorphogenesis. Mutants deficient in four of the five phytochromes have now been isolated. Their analysis indicates considerable overlap in the physiological functions of different phytochromes. In addition, mutants defining components acting downstream of the phytochromes have provided evidence that different members of the family use different signalling pathways.
The neuromuscular control of birdsong
Authors: Suthers Roderick , Goller Franz , Pytte Carolyn
Published: July 2002

Birdsong requires complex learned motor skills involving the coordination of respiratory, vocal organ and craniomandibular muscle groups. Recent studies have added to our understanding of how these vocal subsystems function and interact during song production. The respiratory rhythm determines the temporal pattern of song. Sound is produced during expiration and each syllable is typically followed by a small inspiration, except at the highest syllable repetition rates when a pattern of pulsatile expiration is used. Both expiration and inspiration are active processes. The oscine vocal organ, the syrinx, contains two separate sound sources at the cranial end of each bronchus, each with independent motor control. Dorsal syringeal muscles regulate the timing of phonation by adducting the sound–generating labia into the air stream. Ventral syringeal muscles have an important role in determining the fundamental frequency of the sound. Different species use the two sides of their vocal organ in different ways to achieve the particular acoustic properties of their song. Reversible paralysis of the vocal organ during song learning in young birds reveals that motor practice is particularly important in late plastic song around the time of song crystallization in order for normal adult song to develop. Even in adult crystallized song, expiratory muscles use sensory feedback to make compensatory adjustments to perturbations of respiratory pressure. The stereotyped beak movements that accompany song appear to have a role in suppressing harmonics, particularly at low frequencies.
Genetic hitchhiking
Authors: Barton N. H.
Published: July 2002

Selection on one or more genes inevitably perturbs other genes, even when those genes have no direct effect on fitness. This article reviews the theory of such genetic hitchhiking, concentrating on effects on neutral loci. Maynard Smith and Haigh introduced the classical case where the perturbation is due to a single favourable mutation. This is contrasted with the apparently distinct effects of inherited variation in fitness due to loosely linked loci. A model of fluctuating selection is analysed which bridges these alternative treatments. When alleles sweep between extreme frequencies at a rateλ, the rate of drift is increased by a factor (1 +E[1/pq]λ/(2(2λ+r))), where the recombination rateris much smaller than the strength of selection. In spatially structured populations, the effects of any one substitution are weaker, and only cause a local increase in the frequency of a neutral allele. This increase depends primarily on the rate of recombination relative to selection (r/s), and more weakly, on the neighbourhood size,Nb= 4πρσ2. Spatial subdivision may allow local selective sweeps to occur more frequently than is indicated by the overall rate of molecular evolution. However, it seems unlikely that such sweeps can be sufficiently frequent to increase significantly the drift of neutral alleles.
Begging and bleating: the evolution of parent–offspring signalling
Authors: Godfray H. C. J. , Johnstone R. A.
Published: July 2002

The evolution of biological signalling in the face of evolutionary conflicts of interest is an active area of evolutionary ecology, and one to which Maynard Smith has made important contributions. We explore the major theoretical challenges in the field, concentrating largely on how offspring signal to their parents when there is the potential for parent–offspring conflict. Costly offspring solicitation (begging etc.) has been interpreted in terms of a Zahavi–Grafen honest handicap signal, but this has been challenged on the grounds of the costs of signalling. We review this controversy and also explore the issue of pooling versus separating signalling equilibrium. An alternative explanation for costly begging is that it is due to sibling competition, and we discuss the relationship between these ideas and signalling models in families with more than one offspring. Finally we consider signal uncertainty, how signalling models can be made dynamic, and briefly how they may be tested experimentally.
Molybdenum, rhodium, and tungsten anode spectral models using interpolating polynomials with application to mammography
Authors: Boone John M. , Fewell Thomas R. , Jennings Robert J.
Published: July 2002

Computer simulation is a convenient and frequently used tool in the study of x‐ray mammography, for the design of novel detector systems, the evaluation of dose deposition, x‐ray technique optimization, and other applications. An important component in the simulation process is the accurate computer‐generation of x‐ray spectra. A computer model for the generation of x‐ray spectra in the mammographic energy range from 18 kV to 40 kV has been developed. The proposed model requires no assumptions concerning the physics of x‐ray production in an x‐ray tube, but rather makes use of x‐ray spectra recently measured experimentally in the laboratories of the Center for Devices and Radiological Health. Using x‐ray spectra measured for molybdenum, rhodium, and tungsten anode x‐ray tubes at 13 different kV's (18, 20, 22,…,42 kV), a spectral model using interpolating polynomials was developed. At each energy in the spectrum, the x‐ray photon fluence was fit using 2, 3, or 4 term (depending on the energy) polynomials as a function of the applied tube voltage (kV). Using the polynomial fit coefficients determined at each 0.5 keV interval in the x‐ray spectrum, accurate x‐ray spectra can be generated for any arbitrary kV between 18 and 40 kV. Each anode material (Mo, Rh, W) uses a different set of polynomial coefficients. The molybdenum anode spectral model using interpolating polynomials is given the acronym MASMIP, and the rhodium and tungsten spectral models are called RASMIP and TASMIP, respectively. It is shown that the mean differences in photon fluence calculated over the energy channels and over the kV range from 20 to 40 kV were for MASMIP, for RASMIP, and for TASMIP. The polynomial coefficients for all three models are given in an Appendix. A short C subroutine which uses the polynomial coefficients and generates x‐ray spectra based on the proposed model is available on the World Wide Web at http://www.aip.org/epaps/epaps.html.
Application of AAPM Radiation Therapy Committee Task Group 23 test package for comparison of two treatment planning systems for photon external beam radiotherapy
Authors: Alam Rejina , Ibbott Geoffrey S. , Pourang Rahman , Nath Ravinder
Published: July 2002

Task Group 23 of the AAPM Radiation Therapy Committee has produced a test package for verification of the accuracy of treatment planning for photon external beam therapy. The package includes measured fundamental beam data for 4 and 18 MV x rays, and 13 test cases with measured dose values at selected points, which serve as the reference for determination of calculated dose accuracy. Test cases include three square fields, two rectangular fields, a wedged field, a blocked field, and an irregular field, as well as cases of an off‐center plane, source‐to‐surface distance (SSD) variation, oblique incidence, and lung and bone inhomogeneities. This package was used to evaluate two treatment planning systems. Although average dose variations in most cases were less than 1%, maximum deviations up to 19% were observed in one planning system and up to 11% in the other. Dose deviations greater than 3% were observed for 51 of 532 points (in the 4 MV case) and for 124 of 586 points (in the 18 MV case). An additional component of the test package is an evaluation of radiological field width at different depths. The largest deviation for width was 17.4 mm for 4 MV and 9.1 mm for 18 MV. In 20% of the widths studied, the deviation observed was greater than 3 mm for the 4 MV case. In the 18 MV case 18% of the widths had deviations greater than 3 mm. Our data indicate that the accuracy of the two treatment planning systems tested here warrants improvement, even for simple treatment geometries involving photon beams, which are generally considered to be well understood. As one of the treatment planning systems is widely used in the US, it is concluded that the accuracy of the currently available commercial treatment planning systems is not adequate for achieving the generally stated goal of accuracy of dose delivery in radiation therapy. The AAPM Task Group 23 test package provides an extremely useful tool for a quantitative analysis of treatment planning systems for photon beam radiation therapy.
Advanced single‐slice rebinning in cone‐beam spiral CT
Authors: Kachelrieß Marc , Schaller Stefan , Kalender Willi A.
Published: July 2002

To achieve higher volume coverage at improved z‐resolution in computed tomography (CT), systems with a large number of detector rows are demanded. However, handling an increased number of detector rows, as compared to today's four‐slice scanners, requires to accounting for the cone geometry of the beams. Many so‐called cone‐beam reconstruction algorithms have been proposed during the last decade. None met all the requirements of the medical spiral cone‐beam CT in regard to the need for high image quality, low patient dose and low reconstruction times. We therefore propose an approximate cone‐beam algorithm which uses virtual reconstruction planes tilted to optimally fit 180° spiral segments, i.e., the advanced single‐slice rebinning (ASSR) algorithm. Our algorithm is a modification of the single‐slice rebinning algorithm proposed by Noo et al. [Phys. Med. Biol. 44, 561–570 (1999)] since we use tilted reconstruction slices instead of transaxial slices to approximate the spiral path. Theoretical considerations as well as the reconstruction of simulated phantom data in comparison to the gold standard 180°LI (single‐slice spiral CT) were carried out. Image artifacts, z‐resolution as well as noise levels were evaluated for all simulated scanners. Even for a high number of detector rows the artifact level in the reconstructed images remains comparable to that of 180°LI. Multiplanar reformations of the Defrise phantom show none of the typical cone‐beam artifacts usually appearing when going to larger cone angles. Image noise as well as the shape of the respective slice sensitivity profiles are equivalent to the single‐slice spiral reconstruction, z‐resolution is slightly decreased. The ASSR has the potential to become a practical tool for medical spiral cone‐beam CT. Its computational complexity lies in the order of standard single‐slice CT and it allows to use available 2D backprojection hardware.
The Galilean covariance of quantum mechanics in the case of external fields
Authors: Brown Harvey R. , Holland Peter R.
Published: July 2002

Textbook treatments of the Galilean covariance of the time-dependent Schrödinger equation for a spinless particle seem invariably to cover the case of a free particle or one in the presence of a scalar potential. The principal objective of this paper is to examine the situation in the case of arbitrary forces, including the velocity-dependent variety resulting from a vector potential. To this end, we revisit the 1964 theorem of Jauch which purports to determine the most general form of the Hamiltonian consistent with “Galilean-invariance,” and argue that the proof is less than compelling. We then show systematically that the Schrödinger equation in the case of a Jauch-type Hamiltonian is Galilean covariant, so long as the vector and scalar potentials transform in a certain way. These transformations, which to our knowledge have appeared very rarely in the literature on quantum mechanics, correspond in the case of electrodynamical forces to the “magnetic” nonrelativistic limit of Maxwell’s equations in the sense of Le Bellac and Lévy-Leblond (1973). Finally, this Galilean covariant theory sheds light on Feynman’s “proof” of Maxwell’s equations, as reported by Dyson in 1990.
Source ranging with minimal environmental information using a virtual receiver and waveguide invariant theory
Authors: Thode Aaron M.
Published: July 2002

A method is presented for estimating the range of an unknown broadband acoustic source in a waveguide, using a vertical array and a signal sample from another broadband source at a known location relative to the array. The method requires no modeling of the acoustic field, and little to no environmental information for flat bathymetries. Waveguide invariant theory [e.g., D’Spain and Kuperman, J. Acoust. Soc. Am 106, 2454–2468 (1999)] is applied to the “virtual receiver” [Siderius et al., J. Acoust. Soc. Am. 102, 3439–3449 (1997)] to create a “virtual aperture” (VA). In effect, the method effectively converts a source at known range rg into a continuum of receivers lying between ranges (1±α/β)*rg, where β is a scalar parameter called the acoustic invariant, and α∼0.1. This effective displacement is achieved by correlating the known source field, measured at frequency component ω, with the unknown source field, measured at frequency component ω+ωs. When the VA output is plotted as a function of ω and ωs, the slope of the resulting correlation contours yields the unknown source range. The concept is illustrated via both simulation and analysis of data collected from a pseudo-random noise source with 75–150-Hz bandwidth during SWellEx-3, a shallow water experiment conducted off the San Diego coast. The virtual aperture can be reformulated for range-dependent environments, if adiabatic propagation assumptions are valid, and if the bathymetry surrounding the array is known.
The relationship of vocal tract shape to three voice qualities
Authors: Story Brad H. , Titze Ingo R. , Hoffman Eric A.
Published: July 2002

Three-dimensional vocal tract shapes and consequent area functions representing the vowels [i, æ, ɑ, u] have been obtained from one male and one female speaker using magnetic resonance imaging (MRI). The two speakers were trained vocal performers and both were adept at manipulation of vocal tract shape to alter voice quality. Each vowel was performed three times, each with one of the three voice qualities: normal, yawny, and twangy. The purpose of the study was to determine some ways in which the vocal tract shape can be manipulated to alter voice quality while retaining a desired phonetic quality. To summarize any overall tract shaping tendencies mean area functions were subsequently computed across the four vowels produced within each specific voice quality. Relative to normal speech, both the vowel area functions and mean area functions showed, in general, that the oral cavity is widened and tract length increased for the yawny productions. The twangy vowels were characterized by shortened tract length, widened lip opening, and a slightly constricted oral cavity. The resulting acoustic characteristics of these articulatory alterations consisted of the first two formants (F1 and F2) being close together for all yawny vowels and far apart for all the twangy vowels.
Time reversal for a single spherical scatterer
Authors: Chambers David H. , Gautesen A. K.
Published: July 2002

We show that the time reversal operator for a planar time reversal mirror (TRM) can have up to four distinct eigenvalues with a small spherical acoustic scatterer. Each eigenstate represents a resonance between the TRM and an induced scattering moment of the sphere. Their amplitude distributions on the TRM are orthogonal superpositions of the radiation patterns from a monopole and up to three orthogonal dipoles. The induced monopole moment is associated with the compressibility contrast between the sphere and the medium, while the dipole moments are associated with density contrast. The number of eigenstates is related to the number of orthogonal orientations of each induced multipole. For hard spheres (glass, metals) the contribution of the monopole moment to the eigenvalues is much greater than that of the dipole moments, leading to a single dominant eigenvalue. The other eigenvalues are much smaller, making it unlikely multiple eigenvalues could have been observed in previous experiments using hard materials. However, for soft materials such as wood, plastic, or air bubbles the eigenvalues are comparable in magnitude and should be observable. The presence of multiple eigenstates breaks the one-to-one correspondence between eigenstates and distinguishable scatterers discussed previously by Prada and Fink [Wave Motion 20, 151–163 (1994)]. However, eigenfunctions from separate scatterers would have different phases for their eigenfunctions, potentially restoring the ability to distinguish separate scatterers. Since relative magnitudes of the eigenvalues for a single scatterer are governed by the ratio of the compressibility contrast to the density contrast, measurement of the eigenvalue spectrum would provide information on the composition of the scatterer.
Surface acoustic waves in the GHz range generated by periodically patterned metallic stripes illuminated by an ultrashort laser pulse
Authors: Bonello B. , Ajinou A. , Richard V. , Djemia Ph. , Chérif S. M.
Published: July 2002

The photoelastic response of periodic arrays of stripes attached to the surface of a substrate and illuminated by an ultrashort laser pulse were investigated. The samples were gold arrays on silicon and aluminum arrays either on crystalline quartz or on silicon. The metallic stripes had submicrometer lateral dimensions and the spatial periods ranged from about 1 μm up to 5 μm. The substrate being transparent (quartz) or slightly absorbing (silicon) at the laser wavelength (λ=750 nm), a laterally modulated thermal stress is generated near the surface of the substrate when a light pulse illuminates the structure. The studies of vibrations involved by the subsequent relaxation processes show that surface acoustic waves at frequency as high as about 5 GHz are excited with the samples consisting of aluminum stripes. In the case of the aluminum samples with the largest lateral spatial periods (aluminum on quartz), the surface acoustic wave propagates outside the illuminated area. In the case of the gold samples, a normal mode of individual bars is observed instead. Experimental evidence shows that these behaviors are mainly governed both by the lateral spatial period of the structure and by the density of the metal.
Source depth and the spatial coherence of ambient noise in the ocean
Authors: Buckingham Michael J. , Carbone Nicholas M.
Published: July 2002

An analytical model is developed for the vertical coherence of the ambient noise field generated by a plane of sources at a finite depth beneath the ocean surface. To clarify the effects of source depth on the noise field, the relatively simple case of a semi-infinite ocean with an isovelocity profile is considered. The expression derived for the coherence is exact; it depends on the source depth explicitly, and it includes the homogeneous and inhomogeneous components of the field. When the sources are shallow, that is, the source depth is much less than a wavelength and the source–image pairs act as dipoles, the coherence is an oscillatory function of frequency, consistent with an earlier theory of noise coherence in deep water. With deeper sources, the dipole description fails and the coherence function becomes approximately independent of frequency. This change of character suggests that the spatial structure of the noise field at depth in the ocean could be inverted to yield information on the acoustic properties of the bubble sources associated with breaking surface waves.
Dynamical surface response of a semi-infinite anisotropic elastic medium to an impulsive force
Authors: Bescond C. , Deschamps M.
Published: July 2002

The dynamical surface response to an impulsive point source or line source at any location on the free surface of an anisotropic half-space is solved. The calculation of the Green’s functions of the elastic homogeneous medium is based on the Cagniard–de Hoop method. This theoretical study models the generation–detection of transient surface acoustic waves with a point source–point receiver or with a line source–point receiver. An inspection of singular points in the complex plane of the phase slownesses points out the striking phenomena due to anisotropy of surface wave propagation. As a result, the propagation of the Rayleigh wave, of the surface skimming waves, and of the pseudosurface wave are studied as well as the wavefronts focusing. In addition, the diffraction effects by the cusps are emphasized.
Rayleigh wave dispersion due to a distribution of semi-elliptical surface-breaking cracks
Authors: Pecorari Claudio
Published: July 2002

A model describing changes of Rayleigh wave velocity caused by distributions of two-dimensional, surface-breaking cracks is presented. The results are obtained by extending an approach recently presented by the same author [C. Pecorari, J. Acoust. Soc. Am. 100, 1542–1550 (1996)] for the analogous problem concerning distributions of one-dimensional cracks. The method developed in the previous article to evaluate the effective elastic constants of a cracked surface is presented here again and its assumptions are discussed in greater detail. A comparison between theoretical predictions and experimental results is also presented.
Acoustic properties of a reed (Arundo donax L.) used for the vibrating plate of a clarinet
Authors: Obataya E. , Norimoto M.
Published: July 2002

The effect of water-soluble extractives on the acoustic properties of a reed (Arundo donax L.) used for the vibrating plate of a clarinet was investigated at various relative humidities (RH). At low RH levels, the extractives enhanced the dynamic Young’s modulus of the reed. This effect was reduced with increasing RH because of the deliquescence of extractives. It was suggested that the quality of the reed is improved by the extractives reinforcing its dry part. The extractives also increase the density and the internal friction of the reed remarkably. These might affect the frequency response of the reed to make the tone richer and softer. The tone quality of the reed lost by the removal of extractives was reproduced by impregnating the reed with glucose, which is the most abundant constituent of natural extractives.
Broadband source localization in shallow water in the presence of internal waves
Authors: Yoo Kwang , Yang T. C.
Published: July 2002

Source localization is a challenging problem in a time-varying random shallow-water environment in the presence of internal waves. The short correlation time of the acoustic field (a couple of minutes) makes it difficult to adjust the replica field in response to the environmental changes. Also, mode couplings induced by the internal waves are random and not predictable. In this paper, the effect of mode coupling on source localization in the presence of Garrett–Munk and solitary internal waves is investigated. It is found that mode coupling affects practically all modes in shallow water. Random-mode coupling reduces the matched-field correlation. To improve source localization, a broadband matched-beam processing algorithm is proposed to suppress the noncoherent coupled-mode contributions. It is shown that this technique significantly improves the localization performance over conventional matched-field processing.
Localization using Bartlett matched-field processor sidelobes
Authors: Thode Aaron M. , Kuperman W. A. , D’Spain G. L. , Hodgkiss W. S.
Published: July 2002

Ambiguity surface sidelobes generated by the Bartlett matched-field processor (MFP) shift location with frequency. This sidelobe shift can be viewed as a continuous trajectory in a range-frequency plane at a fixed depth, where the trajectories converge to the correct source range for a perfectly matched surface. In isovelocity or bottom-interacting environments the sidelobe trajectories are straight lines that converge to the true range at zero frequency, while environments with upward-refracting sound-speed profiles have trajectories that asymptotically converge as the frequency approaches infinity. This behavior can be explained by the theory of waveguide invariants, which predict the local behavior of interference maxima/minima of acoustic intensity in the frequency-range plane. As the ambiguity surface of the Bartlett matched-field processor has a physical interpretation in terms of a time-reversed acoustic field, with the sidelobes analogous to local interference maxima, these invariant concepts can be reformulated for application to MFP. These interference trajectories are demonstrated to exist in simulations, broadband source tows, and a type A blue whale vocalization. Sidelobe trajectories also exist in the range-depth plane, but they contain no information about the correct source depth. An appendix demonstrates how these sidelobe properties can be exploited when combining ambiguity surfaces through use of gradient and Radon transform information. The resulting range estimators demonstrate better peak-to-sidelobe ratios than a simple incoherent average.
Masking by harmonic complexes in budgerigars (Melopsittacus undulatus)
Authors: Leek Marjorie R. , Dent Micheal L. , Dooling Robert J.
Published: July 2002

In humans, masking by harmonic complexes is dependent not only on the frequency content of the masker, but also its phase spectrum. Complexes that have highly modulated temporal waveforms due to the selection of their component phases usually provide less masking than those with flatter temporal envelopes. Moreover, harmonic complexes that are created with negative Schroeder phases (component phases monotonically decreasing with increasing harmonic frequency) may provide more masking than those created with positive Schroeder phases (monotonically increasing phase), even though both temporal envelopes are equally flat. To date, there has been little comparative work on the masking effectiveness of harmonic complexes. Using operant conditioning and the method of constant stimuli, masking of pure tones by harmonic complexes was examined in budgerigars at several different masker levels for complexes constructed with two different fundamental frequencies. In contrast to humans, thresholds in budgerigars differed very little for the two Schroeder-phase waveforms. Moreover, when there was a difference in masking by these two waveforms, the positive Schroeder was the more effective masker—the reverse of that described for humans. Control experiments showed that phase selection was relevant to the masking ability of harmonic complexes in budgerigars. Release from masking occurred when the components were in coherent phase, compared with a complex with random phases selected for each component. It is suggested that these psychoacoustic differences may emerge from structural and functional differences between the avian and mammalian peripheral auditory systems involving traveling wave mechanics and spectral tuning characteristics.
The Dreaded “Twindemic” of Influenza and COVID-19 Has Not Yet Materialized—Might This Be the Year?
Authors: Rubin Rita
Published: September 2022

This Medical News feature discusses the challenges of predicting how severe flu season might be.
Association Between Adverse Childhood Experiences and Posttraumatic Stress Disorder Symptoms in Adults With Injury
Authors: Huffmaster Candace E. , Williams Ashley Y. , Lee Yann-leei L. , Butts C. Caleb , Polite Nathan M. , Mehari Krista R. , Simmons Jon D.
Published: September 2022

This case-control study examines the risk factors associated with acute stress disorder in patients with severe injury.
Seeing is believing? A systematic review of credibility perceptions of live and remote video‐mediated communication in legal settings
Authors: Given‐Wilson Zoe , Memon Amina
Published: September 2022

There has been a dramatic increase in use of remote communication via audio‐visual technology since the COVID‐19 pandemic. This includes use in complex legal hearings where decisions rely heavily on credibility assessments of an individual and their interview statement. This is particularly relevant in legal settings where negative assessments can have adverse outcomes such as asylum applications which can result in deportation. Increasing use of remote communication technology raises the question of what research can tell us about how someone is perceived when interviewed live (in‐person) compared with via video‐mediation. A systematic review of the literature resulted in the selection of nine papers. Four themes were identified; decision‐maker's assumptions, frame of the camera, demeanour and detecting truth and lies. The results are discussed within the context of credibility judgements in asylum proceedings together with implications for further research and practice.
Electric Field Screening in Gate‐Tunable van der Waals 2D‐Metal/InSe Junctions
Authors: Shen Tao , Liu Jia , Liu Xinyi , Cheng Peng , Ren Ji‐Chang , Li Shuang , Liu Wei
Published: September 2022

The prediction of the dielectric response in 2D metal–semiconductor junctions (MSJs) is challenging since the screening is inhomogeneous. Herein, a generalized model is proposed to uncover the relationship between interfacial electrostatic screening and the modulation of Schottky barrier height (ΦSB) in 2D MSJs. This model is developed based on the effective dielectric constant, interfacial distance, and van der Waals gap that sheds light on the profound difference between dielectric screening in 2D and conventional MSJs. This model can predict the variation of ΦSB for a series of 2D MSJs. Combining thermionic field emission theory with the model, several compatible 2D metals are provided for low‐dimensional electronics, among which the α‐graphyne‐based junction exhibits the largest on/off ratio.