bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear delta-f simulations of nonlocal electron heat transport
Authors: Brunner S. , Valeo E. , Krommes J. A.
Published: July 2002

Nonlocal electron heat transport calculations are carried out by making use of some of the techniques developed previously for extending the δf method to transport time scale simulations [S. Brunner, E. Valeo, and J. Krommes, Phys. Plasmas 6, 4504 (1999)]. By considering the relaxation of small amplitude temperature perturbations of an homogeneous Maxwellian background, only the linearized Fokker–Planck equation has to be solved, and direct comparisons can be made with the equivalent, nonlocal hydrodynamic approach [V. Yu. Bychenkov et al., Phys. Rev. Lett. 75, 4405 (1995)]. A quasineutrality-conserving algorithm is derived for computing the self-consistent electric fields driving the return currents. In the low-collisionality regime, results illustrate the importance of taking account of nonlocality in both space and time.
Gravitational collapse in dusty plasmas with mass distributions and neutral gas
Authors: Verheest Frank , Jacobs Gerald , Yaroshenko Victoria V.
Published: July 2002

Jeans and two-stream instabilities are revisited for mixtures of charged and neutral dust, and also for different species of charged dust. From the general dispersion law for different dust species, limiting cases of monodisperse or polydisperse but cold dust components are discussed, putting results from the literature in perspective. Dispersion laws and critical Jeans lengths are then derived for a mixture of two dust species, or of charged and neutral dust, the latter being of interest in interstellar dust clouds where not enough electrons are available to charge all the grains. Instabilities are considered for two counterstreaming dust beams of equal strength, showing how the Jeans and streaming instabilities are coupled in specific wave number domains.
The transition from collisionless to collisional active plasma in the fluid model and the relevance of the Bohm criterion to sheath formation
Authors: Franklin R. N. , Snell J.
Published: July 2002

The fluid equations describing the plasma–wall sheath in an electropositive gas are solved numerically with parameters, δi the ratio of the ion collision frequency νi to the ionization rate Z, and α the ratio of the ionization rate to the ion plasma frequency ωpi. From the behavior of the ion speed and from the plasma balance equation relating the plasma dimension L to Z it is possible to identify regions in α−δi space in which the plasma is (a) collisionless, (b) transitional, and (c) collisional and in which the boundary layer is (i) collisionless and (ii) collisional. The Bohm criterion ceases to have significance when the layer matching plasma and wall becomes collisional.
Ionic excitation in dense, two-component plasmas: A nonperturbative approach
Authors: Kitamura Hikaru , Murillo Michael S. , Weisheit Jon C.
Published: July 2002

A nonperturbative formulation of atomic collisional excitation rates in dense plasmas is developed on the basis of the equations of motion for density matrices in a stochastic potential. This model treats the strong scattering between the atom and plasma particles through the many-body correlation functions describing plasma density fluctuations, which are decomposed into the products of dynamic structure factors within the decorrelation approximation and then are summed to infinite order. A simple analytic solution to the density matrix equation is obtained for two-level atoms. The electron-induced transition of a hydrogen-like ion in dense hydrogen plasma is studied as an example. It is demonstrated that, when the plasma density is sufficiently high, low-frequency ion-density fluctuations influence the electron dynamics and thereby cause coherent excitation between close-lying atomic states. The resultant time evolution of the atomic level population differs considerably from the prediction of one-component plasma collisional rate equations based on first-order perturbation theory (Born approximation).
Methods for producing ultrahigh magnetic fields
Authors: Felber F. S. , Liberman M. A. , Velikovich A. L.
Published: July 2002

A general class of methods is suggested for producing controlled magnetic fields up to the order of 100 MG. The methods involve radially imploding plasmas in which longitudinal magnetic fields have been entrained. Specific methods of implosion suggested are (a) gas-puff Z pinch and (b) ablative implosion of a liner by a laser. Applications include reducing fusion ignition thresholds, producing beams of gamma radiation, accelerating particles, and producing high-energy densities under controlled conditions.
Dependence of critical layer thickness on strain for InxGa1−xAs/GaAs strained-layer superlattices
Authors: Fritz I. J. , Picraux S. T. , Dawson L. R. , Drummond T. J. , Laidig W. D. , Anderson N. G.
Published: July 2002

Various InxGa1−xAs/GaAs strained-layer superlattices have been characterized by Hall effect, ion beam channeling, and photoluminescence measurements in order to evaluate their crystalline quality. Structural characteristics (e.g., layer strains and thicknesses) were obtained from channeling or x-ray diffraction studies. The structures had strains in the alloy layers of 0.5–2.7%. Critical layer thicknesses for degradation of sample quality are in good agreement with the theoretical expression proposed by J. W. Matthews and A. E. Blakeslee [J. Cryst. Growth 27, 118 (1974)]. Our results provide important information for design of strained-layer devices.
High current density plasma cathode
Authors: Humphries S. , Savage M. , Woodall D. M.
Published: July 2002

A grid-controlled plasma cathode has been operated at high current density (15 A/cm2) using vacuum insulator breakdown as the plasma source. The insulator spark generates a highly reproducible, 6-μs plasma pulse with density 1013 cm−3 at a distance of 6 cm. A number of sparks can be driven in parallel to supply large area plasma cathodes.
Spatially resolved defect mapping in semiconductors using laser-modulated thermoreflectance
Authors: Guidotti D. , van Driel H. M.
Published: July 2002

We demonstrate that thermoreflectance can be observed when lattice heating is effected with an amplitude modulated laser. Changes in reflectivity are probed with a cw laser, and maps of inhomogeneous ion implantation and swirl precipitates in Si wafers are obtained.
Composition-selective photochemical etching of compound semiconductors
Authors: Ashby C. I. H. , Biefeld R. M.
Published: July 2002

Compound semiconductor materials differing only in the relative amounts of constituent atoms are very difficult to etch selectively using current chemical etching techniques. We have developed a photochemical etching process that solves this problem by utilizing the difference in band gap of GaAs1−xPx materials differing slightly in composition to produce a very high degree of etching selectivity between the materials. The concepts employed in this process have general applicability to other compound semiconductor material systems.
Effect of dose rate on ion beam mixing in Nb-Si
Authors: Banwell Thomas , Nicolet M-A. , Averback R. S. , Thompson L. J.
Published: July 2002

The influence of dose rate, i.e., ion flux, on ion beam mixing in Nb-Si bilayer samples was measured at room temperature and 325 °C. At the higher temperature, an increase in dose rate of a factor of 20 caused a decrease in the thickness of the mixed layer by a factor of 1.6 for equal total doses. At room temperature, the same change in flux had no effect on mixing. These results are consistent with radiation-enhanced diffusion theory in the recombination-limited regime.
Implosion of sodium-bearing capillary-discharge plasmas for x-ray laser experiments
Authors: Young F. C. , Stephanakis S. J. , Scherrer V. E. , Welch B. L. , Mehlman G. , Burkhalter P. G. , Apruzese J. P.
Published: July 2002

A NaF plasma from a capillary discharge has been imploded with a 1.2-MA driving current to produce an intense source of sodium K-shell x rays. A peak power of 25 GW in a 20-ns pulse was measured for the sodium He-α line which can be used as the pump radiation for a Na/Ne XUV laser scheme.
Trap-Auger recombination in silicon of low carrier densities
Authors: Landsberg P. T.
Published: July 2002

We report an analysis of recent accurate room-temperature lifetime measurments τ as a function of injected electron concentration n (equal to injected hole concentration). Instead of the earlier authors’ fit to a curve τ−1=a+bn2, we have used τ−1=α+βn+γn2, and have given theoretical formulae for α, β, and γ. An excellent fit for 〈100〉 silicon suggests for γ a sum of the electron and hole band-band Auger coefficients∼10−30 cm6 s−1, half the value given earlier, but still larger than the accepted value. The importance of the β term is that it indicated that a trap-band Auger effect plays a part. The relevant recombination coefficient, identified from the fit, has the reasonable value∼10−24 cm6 s−1. The effect seems important in spite of the low residual defect concentration.
Electron population factor in light enhanced oxidation of silicon
Authors: Young E. M. , Tiller William A.
Published: July 2002

Electrons in the electron/hole creation event are shown to be the prime catalytic agent in photon-stimulated oxidation enhancement of silicon. Oxidation enhancement in the 10–50% range occurs at only moderate power density levels of visible wavelength light and increases greatly for photon energies just exceeding the conduction-band edge between SiO2 and Si. ‘‘Hot’’-electron injection into the SiO2 is thought to enhance the oxidation via a process of electron attachment to some of the in-diffusing O2 species, with subsequent dissociation into O and O− species. This injected hot-electron flux reaction with O2 is thought to also occur at a reduced level during standard thermal oxidation.
Synchrotron-radiation-induced surface nitridation of silicon at room temperature
Authors: Cerrina F. , Lai B. , Wells G. M. , Wiley J. R. , Kilday D. G. , Margaritondo G.
Published: July 2002

We demonstrate that unmonochromatized synchrotron radiation stimulates the formation of surface-reacted nitride species on silicon at room temperature. The experimental evidence was obtained by exposing a NH3-covered Si(111) surface to synchrotron radiation. This class of phenomena is relevant for the manufacturing technology of submicron electronic devices.
Performance of a fully superconducting microwave cavity made of the high T
c superconductor Y1Ba2Cu3Oy
Authors: Zahopoulos C. , Kennedy W. L. , Sridhar S.
Published: July 2002

We report the successful fabrication and characterization of a high Tc superconducting microwave cavity. The cavity made of bulk Y1Ba2Cu3Oy (Tc=93 K) and dielectrically loaded with sapphire was resonant at 8.00 GHz in the TE011 mode. At 77 K the Q was 104, which represents an improvement of a factor of 11 from the normal state. At 4.2 K the Q was nearly 105. The temperature dependence of the Q correlates extremely well with the microwave surface resistance of a test sample measured independently, clearly showing that the Q was limited by the intrinsic materials preparation and not by extraneous factors.
Passivation of zinc acceptors in InP by atomic hydrogen coming from arsine during metalorganic vapor phase epitaxy
Authors: Antell G. R. , Briggs A. T. R. , Butler B. R. , Kitching S. A. , Stagg J. P. , Chew A. , Sykes D. E.
Published: July 2002

The passivation of zinc acceptors in InP has been observed, originally in zinc-doped InGaAs/InP heterostructures. Evidence is presented to show that hydrogen, which has been detected by secondary ion mass spectrometry, is responsible for the phenomenon and that the source of atomic hydrogen is the arsine used in the epitaxial process. The hydrogen is bound within the epitaxial layers during the cooling down stage after growth is complete.
Electroreflectance study of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy
Authors: Nishino T. , Inoue Y. , Hamakawa Y. , Kondow M. , Minagawa S.
Published: July 2002

We have measured the electroreflectance spectra of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy. As a result, it has been found that there exist anomalous structures in the region of the E0 and E1 band edges of this material. These anomalous structures are closely related to the recently reported ordered phase in this alloy, since these structures have never been observed with disordered Ga0.5In0.5P alloys such as bulk crystals and epitaxial layers grown by liquid phase epitaxy.
Solid phase epitaxy of laser amorphized silicon
Authors: Custer J. S. , Thompson Michael O. , Bucksbaum P. H.
Published: July 2002

The solid phase epitaxial regrowth kinetics of laser amorphized [100] silicon-on-sapphire was studied using in situ time-resolved optical transmission. Regrowth rates for ≤20-nm-thick amorphous silicon films were observed to increase from 1.7×10−10 cm/s at 750 K to 1.9×10−7 cm/s at 900 K. The recrystallization velocity followed an Arrhenius behavior with an activation enthalpy of 2.71 eV. These results provide strong confirmation that the metastable phase quenched following laser irradiation is structurally equivalent to amorphous silicon produced by ion implantation or ultrahigh vacuum deposition, and is not stabilized by impurities.
Advances in random matrix theory, zeta functions, and sphere packing
Authors: Hales T. C. , Sarnak P. , Pugh M. C.
Published: July 2002

Over four hundred years ago, Sir Walter Raleigh asked his
mathematical assistant to find formulas for the number of cannonballs
in regularly stacked piles. These investigations aroused the curiosity
of the astronomer Johannes Kepler and led to a problem that has gone
centuries without a solution: why is the familiar cannonball stack the
most efficient arrangement possible? Here we discuss the solution that
Hales found in 1998. Almost every part of the 282-page proof relies on
long computer verifications. Random matrix theory was developed by
physicists to describe the spectra of complex nuclei. In particular,
the statistical fluctuations of the eigenvalues (“the energy
levels”) follow certain universal laws based on symmetry types. We
describe these and then discuss the remarkable appearance of these laws
for zeros of the Riemann zeta function (which is the generating
function for prime numbers and is the last special function from the
last century that is not understood today.) Explaining this phenomenon
is a central problem. These topics are distinct, so we present them
separately with their own introductory remarks.
Skn-1: Evidence for a bipartite recognition helix in DNA binding
Authors: Pal Santona , Lo Mei-Chu , Schmidt Darby , Pelczer István , Thurber Stacy , Walker Suzanne
Published: July 2002

Skn-1 is a maternally expressed transcription factor that specifies the fate of certain blastomeres early in the development of
Caenorhabditis elegans
. This transcription factor contains a basic region, but it binds to DNA as a monomer. Because other transcription factors containing basic regions bind as dimers, this finding implied that Skn represents a new DNA recognition motif. It has been proposed that the basic region helix of Skn is stabilized for binding by tertiary contacts to other parts of the protein. We have tested this proposal by carrying out circular dichroism (CD) and NMR experiments on the Skn domain and five truncated proteins. Our results have shown that the basic region of Skn is unstructured in solution and does not contact other parts of the protein; like other basic region peptides, it folds into a helix only upon binding specifically to DNA. However, there is a stably folded helical module in the Skn domain, and one of the helices in this module terminates immediately before the start of the basic region. This pre-organized helix contains a surface rich in basic amino acids, and we propose that this helix contacts the DNA distal to the basic region proper, providing an extra long helical recognition surface which helps to stabilize monomeric binding. Homology between the Skn domain and several basic-region leucine zipper (bZIP) domains raises the possibility that the affinity and perhaps the specificity of DNA binding by bZIP proteins can be modulated by incorporating a stably folded helical segment that contacts the DNA just below the basic region proper.
Positron-emission tomography imaging of long-term shape recognition challenges
Authors: Rosier A. , Cornette L. , Dupont P. , Bormans G. , Michiels J. , Mortelmans L. , Orban G. A.
Published: July 2002

Long-term visual memory performance was impaired by two types of challenges: a diazepam challenge on acquisition and a sensory challenge on recognition. Using positron-emission tomography regional cerebral blood flow imaging, we studied the effect of these challenges on regional brain activation during the delayed recognition of abstract visual shapes as compared with a baseline fixation task. Both challenges induced a significant decrease in differential activation in the left fusiform gyrus, suggesting that this region is involved in the automatic or volitional comparison of incoming and stored stimuli. In contrast, thalamic differential activation increased in response to memory challenges. This increase might reflect enhanced retrieval attempts as a compensatory mechanism for restoring recognition performance.
Structural correlations in protein folding funnels
Authors: Shoemaker Benjamin A. , Wang Jin , Wolynes Peter G.
Published: July 2002

While the overall energy landscape of a foldable protein can be
described by means of a few parameters characterizing its statistical
topography, specific energetic terms subtly bias the representative
structures giving rise to residue pair correlations as in a liquid. We
use a free energy functional incorporating an inhomogeneous pair
contact energy along with a contact formation entropy and a
cooperativity contribution to determine residue-specific contact
probabilities in the denatured state and the transition state ensemble.
The predicted “hot residues” for the theoretical transition state
ensemble reasonably agree with experiment for chymotrypsin
inhibitor 2, and generally a strong correlation exists with the
measured kinetic effects of mutating residues not involved in highly
solvent-exposed regions.
Atmospheric weathering and silica-coated feldspar: Analogy with zeolite molecular sieves, granite weathering, soil formation, ornamental slabs, and ceramics
Authors: Smith Joseph V.
Published: July 2002

Feldspar surfaces respond to chemical, biological, and mechanical weathering. The simplest termination is hydroxyl (OH), which interacts with any adsorption layer. Acid leaching of alkalis and aluminum generated a silica-rich, nanometers-thick skin on certain feldspars. Natural K, Na-feldspars develop fragile surfaces as etch pits expand into micrometer honeycombs, possibly colonized by lichens. Most crystals have various irregular coats. Based on surface-catalytic processes in molecular sieve zeolites, I proposed that some natural feldspars lose weakly bonded Al-OH (aluminol) to yield surfaces terminated by strongly bonded Si-OH (silanol). This might explain why some old feldspar-bearing rocks weather slower than predicted from brief laboratory dissolution. Lack of an Al-OH infrared frequency from a feldspar surface is consistent with such a silanol-dominated surface. Raman spectra of altered patches on acid-leached albite correspond with amorphous silica rather than hydroxylated silica–feldspar, but natural feldspar may respond differently. The crystal structure of H-exchanged feldspar provides atomic positions for computer modeling of complex ideas for silica-terminated feldspar surfaces. Natural weathering also depends on swings of temperature and hydration, plus transport of particles, molecules, and ionic complexes by rain and wind. Soil formation might be enhanced by crushing granitic outcrops to generate new Al-rich surfaces favorable for chemical and biological weathering. Ornamental slabs used by architects and monumental masons might last longer by minimizing mechanical abrasion during sawing and polishing and by silicifying the surface. Silica-terminated feldspar might be a promising ceramic surface.
Short-term correction of factor VIII deficiency in a murine model of hemophilia A after delivery of adenovirus murine factor VIIIin utero
Authors: Lipshutz G. S. , Sarkar R. , Flebbe-Rehwaldt L. , Kazazian H. , Gaensler K. M. L.
Published: July 2002

Development ofin uterogene transfer approaches may provide therapies for genetic disorders with perinatal morbidity. In hemophilia A, prenatal and postnatal bleeding may be catastrophic, and modest increments in factor VIII (FVIII) activity are therapeutic. We performed transuterine i.p. gene transfer at day 15 of gestation in a murine model of hemophilia A. Normal, carrier (XHX), and FVIII-deficient (XHY and XHXH) fetuses injected with adenoviral vectors carrying luciferase or β-galactosidase reporter genes showed high-level gene expression with 91% fetal survival. The live-born rates of normal and FVIII-deficient animals injectedin uterowith adenovirus murine FVIII (3.3 × 105plaque-forming units) was 87%. FVIII activity in plasma was 50.7 ± 10.5% of normal levels at day 2 of life, 7.2 ± 2.2% by day 15 of life, and no longer detectable at day 21 of life in hemophilic animals. Injection of higher doses of murine FVIII adenovirus at embryonic day 15 produced supranormal levels of FVIII activity in the neonatal period. PCR analysis identified viral genomes primarily in the liver, intestine, and spleen, although adenoviral DNA was detected in distal tissues when higher doses of adenovirus were administered. These studies show that transuterine i.p. injection of adenoviral vectors produces therapeutic levels of circulating FVIII throughout the neonatal period. The future development of efficient and persisting vectors that produce long-term gene expression may allow forin uterocorrection of genetic diseases originating in the fetal liver, hematopoietic stem cells, as well as other tissues.
Very large radio surveys of the sky
Authors: Condon J. J.
Published: July 2002

Recent advances in electronics and
computing have made possible a new generation of large radio surveys of
the sky that yield an order-of-magnitude higher sensitivity and
positional accuracy. Combined with the unique properties of the radio
universe, these quantitative improvements open up qualitatively
different and exciting new scientific applications of radio surveys.
Effects of unique ion chemistry on thin-film growth by plasma–surface interactions
Authors: Wijesundara Muthu B. J. , Hanley Luke , Ni Boris , Sinnott Susan B.
Published: July 2002

Plasma processing is a standard industrial method for the modification of material surfaces and the deposition of thin films. Polyatomic ions and neutrals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the deposition of polymeric films from fluorocarbon plasmas. In this paper, low energy CF
3
+
and C
3
F
5
+
ions are used to modify a polystyrene surface. Experimental and computational studies are combined to quantify the effect of the unique chemistry and structure of the incident ions on the result of ion-polymer collisions. C
3
F
5
+
ions are more effective at growing films than CF
3
+
, both at similar energy/atom of ≈6 eV/atom and similar total kinetic energies of 25 and 50 eV. The composition of the films grown experimentally also varies with both the structure and kinetic energy of the incident ion. Both C
3
F
5
+
and CF
3
+
should be thought of as covalently bound polyatomic precursors or fragments that can react and become incorporated within the polystyrene surface, rather than merely donating F atoms. The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking probabilities, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger species contribute to the deposition of polymeric films from fluorocarbon plasmas. These results indicate that complete understanding and accurate computer modeling of plasma–surface modification requires accurate measurement of the identities, number densities, and kinetic energies of higher mass ions and energetic neutrals.
A 12(
S
)-hydroxyeicosatetraenoic acid receptor interacts with steroid receptor coactivator-1
Authors: Kurahashi Yuko , Herbertsson Helena , Söderström Mats , Rosenfeld Michael G. , Hammarström Sven
Published: July 2002

Lewis lung carcinoma cells contain specific high-affinity binding sites for the eicosanoid 12(
S
)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(
S
)-HETE]. These binding sites have a cytosolic/nuclear localization and contain the heat shock proteins hsp70 and hsp90 as components of a high molecular weight cytosolic binding complex. The ligand binding subunit of this complex is a protein with an apparent molecular mass of
≈
50 kDa as judged by gel permeation chromatography. In this report, we present data showing that the 50-kDa 12(
S
)-HETE binding protein interacts as a homodimer with steroid receptor coactivator-1 (SRC-1) in the presence of 12(
S
)-HETE. Two putative interaction domains were mapped. One of these (amino acids 701–781) was within the nuclear receptor interaction domain in SRC-1 required for binding of various steroid and thyroid hormone receptors. It contains the most C-terminal of the three copies of LXXLL motif present in the nuclear receptor interaction domain. The second interaction domain was present in the N-terminal part of SRC-1 (amino acids 1–221). This region has two LXXLL motifs, one does not bind and the other binds only weakly to steroid and thyroid hormone receptors. Glutathione
S
-transferase (GST) pulldown experiments and far Western analyses demonstrated that the N-terminal region of SRC-1 (amino acids 1–212) alone does not bind the 50-kDa 12(
S
)-HETE binding protein, whereas GST/ΔSRC-1
1–1138
ligand-dependently pulled down a protein of ≈50 kDa in size. Our results suggest that the 50-kDa 12(
S
)-HETE binding protein is a receptor that may signal through interaction with a nuclear receptor coactivator protein.
Online peer review: perceptions in the biological sciences
Authors: Wood Dee , Hurst Phil
Published: July 2002

An experiment in online peer review was carried out by the Royal Society, on the journal Proceedings: Biological Sciences. Authors were asked to provide Acrobat PDF files and uploaded them using a web interface. Referees were provided with a URL that gave access to the paper and entered their report into an online form. Almost 50% of the authors contacted used the online method and referees greeted the method with enthusiasm. Editorial staff found the online system easier than expected and were keen to continue its use.
ATHENS, gateways, and portals: components of the Distributed National Electronic Resource
Authors: Wise Alicia , Rusbridge Chris , Wiseman Norman
Published: July 2002

The Distributed National Electronic Resource is a central plank of the UK's Joint Information Systems Committee's strategy. We outline the background and definitions of the DNER and discuss some of the issues to be investigated and the collaboration required between stakeholders and their partners.
No such thing as a mature journal
Authors: Baggaley Richard
Published: July 2002

This article looks at the general idea of developing journals by adding value. It focuses in particular on the notion of the ‘mature journal’ – possibly a mythical beast, but one which most publishing houses will have at least one of (even if they don't know it yet). The article touches on some run‐of‐the‐mill journal issues such as obesity, sex, and death, but will hopefully also throw new light on a corner of the publishing world previously thought of as ‘dull’.
Reviews
Authors: Palmer Richard , Corrigan Adrian
Published: July 2002

Book review: Publish or Perish (2nd edn), ed. Philip Hills

Publish or Perish (2nd edn), ed. Philip Hills. UK: Peter Francis, 1999. ISBN 1 870167 31 7. xviii + 138pp. £21.95. Hardback. Software review Global Editor
Instant linking — delayed use: setting provider expectations
Authors: Pullinger David
Published: July 2002

The web with its hyperlinking is a great environment in which to put electronic journals and to encourage linking of texts. But reference links will only be used substantially if readers incorporate them into new patterns of habitual use. In doing so, many users will be in search mode and only some types of user will habitually use reference linking. There needs to be a sufficient number of references that are linked, the right processes to achieve that efficiently, and something that is worthwhile at the end of the link. Ideally users would get full text and some new business models are suggested that match what users do and the new technical possibilities. All these factors point to the need for patience among providers, rather than expecting to see instant substantial use by e‐journal users.
Phragmén-Lindelöf principles on algebraic varieties
Authors: Meise R. , Taylor B. , Vogt D.
Published: July 2002

Estimates of Phragmén–Lindelöf (PL) type for plurisubharmonic functions on algebraic varieties in

C

n

\mathbb {C}^n

have been of interest for a number of years because of their equivalence with certain properties of constant coefficient partial differential operators; e.g. surjectivity, continuation properties of solutions and existence of continuous linear right inverses. Besides intrinsic interest, their importance lies in the fact that, in many cases, verification of the relevant PL-condition is the only method to check whether a given operator has the property in question. In the present paper the property

P
L

(

R

n

,
ω
)

{PL}({\mathbb R}^n,\omega )

which characterizes the existence of continuous linear right inverses is investigated. It is also the one closest in spirit to the classical Phragmén–Lindelöf Theorem as various equivalent formulations for homogeneous varieties show. These also clarify the relation between

P
L

(

R

n

,
ω
)

{PL}({\mathbb R}^n,\omega )

and the PL-condition used by Hörmander to characterize the surjectivity of differential operators on real-analytic functions. We prove the property

P
L

(

R

n

,
ω
)

{PL}({\mathbb R}^n,\omega )

for an algebraic variety

V
V

implies that

V
h

V_h

, the tangent cone of

V
V

at infinity, also has this property. The converse implication fails in general. However, if

V
h

V_h

is a manifold outside the origin, then

V
V

satisfies

P
L

(

R

n

,
ω
)

{PL}({\mathbb R}^n,\omega )

if and only if the real points in

V
h

V_h

have maximal dimension and if the distance of

z
∈
V

z\in V

to

V
h

V_h

is bounded by

C
ω
(

|

z

|

)

C\omega (|z|)

as

z
z

tends to infinity. In the general case, no geometric characterization of the algebraic varieties which satisfy

P
L

(

R

n

,
ω
)

{PL}({\mathbb R}^n,\omega )

is known, nor any of the other PL-conditions alluded to above. Besides these main results the paper contains several auxiliary necessary conditions and sufficient conditions which make it possible to treat interesting examples completely. Since it was submitted they have been applied by several authors to achieve further progress on questions left open here.
A major component approach to presenting consensus sequences.
Authors: Smith D K , Xue H
Published: July 2002

MOTIVATION: Summarizing and displaying the information contained in a set of aligned sequences is an important aid to identifying patterns within the sequences. A variety of forms of consensus sequences have been used previously to provide this information. However, these methods can cause a loss of information or introduce ambiguities into the consensus sequence, and some graphical approaches may become difficult to interpret due to visual distortion. RESULTS: We have developed a method to present a more precise and graphically clear view of a consensus sequence by using an approach based on defining the major components at each position in a sequence set. The major components are given in an ordered list and their frequencies are shown as histograms which can be colour coded to reflect conservative groupings. Minor components, a one-line character-based consensus sequence and information statistics can also be presented. As well as identifying the dominant sources of variation and conservation in the sequence set, the method also enables similarities and differences between subgroups of a sequence set to be readily assessed. AVAILIABILITY: On request from the authors. CONTACT: bcsmith@usthk.ust.hk, hxue@usthk. ust.hk
MEICPS: substitution mutations to engineer intracellular protein stability.
Authors: Reddy B V , Ramesh P , Tiwari S
Published: July 2002

SUMMARY: In MEICPS, results from earlier analyses are utilized to suggest possible substitution point mutations to engineer intracellular stability using a given sequence or structure of the protein. AVAILABILITY: From bvbreddy@ccmb.ap.nic.in. This program needs data from other software, PSA and SSTRUC, available from sali@tamika.rockefeller.edu and tom@cryst.bioc.cam.ac.uk, respectively. CONTACT: bvbreddy@ccmb.ap.nic.in
MIAH: automatic alignment of eukaryotic SSU rRNAs.
Authors: Th√©bault P , Monesti√© P , McGrath A , Higgins D G
Published: July 2002

SUMMARY: MIAH is a WWW server for the automatic alignment of new eukaryotic SSU rRNA sequences to an existing alignment of 1500 sequences. AVAILABILITY: http://chah.ucc.ie/MIAH Contact :
Matching amino acid and nucleotide sequences of mouse
rheumatoid factor CDRH3-FRH4 segments to other mouse antibodies with
known specificities
Authors: Johnson George , Wu Tai T.
Published: July 2002

Contact: t-wu@nwu.edu

** To whom correspondence should be addressed. E267, Technological Institute, 2145 Sheridan Road, Evanston, IL 60208, USA.
Mathematica packages for simulation of experimental genetics
Authors: Manly Kenneth F.
Published: July 2002

Summary: This note describes add-on packages for the Mathematica software system (Wolfram 1996) which allow simulation and analysis of both Mendelian and complex genetic traits in experimental crosses of plants or animals.

Availability: The add-on packages are freely available at http://www.mathsource.com/cgi-bin/msitem?0209-304.

Contact: kmanly@mcbio.med.buffalo.edu

Supplementary Information: A tutorial notebook file is included with the packages at the mathsource site.
SIR: a simple indexing and retrieval system for biological flat
file databases
Authors: Ramu Chenna
Published: July 2002

Summary: SIR is a Simple Indexing and Retrieval tool for indexing and searching biological flat file databases. SIR is a cross-platform solution entirely written in Python. Since the package is very small and installation is trivial, this would be an ideal solution for database providers to provide a custom retrieval tool to access them.

Availability: The modules will be made available at http://www.EMBLHeidelberg.de/~chenna/PySAT/sir.html

Contact: chenna@EMBL-Heidelberg.de
Implementation of an in vivo diode dosimetry program and changes in diode characteristics over a 4‐year clinical history
Authors: Jursinic Paul A.
Published: July 2002

An in vivo dosimetry system that used n‐type semiconductor diodes with integral build‐up caps was introduced into the clinic. Measurements were made on the entrance surface of the patient and were compared to calculated diode readings expected from monitor units delivered by each beam. A method is given for calibration and correction for changes in diode sensitivity, dose‐per‐pulse effects, collimated field‐size (head‐scatter factor), wedges, compensators, and scatter from blocks and block trays. Clinically relevant temperature corrections are determined based on temperature measurements made with the diode used as a thermistor. Changes in diode characteristics over 4 years of clinical use are presented. With proper correction for clinical variables it is shown that difference between calculated and measured diode readings are within ±1% for phantom measurements and within ±3% for clinical measurements at a 95% confidence level. The correlation of dose measurements on the patient surface to dose inside a target volume is discussed.
A generalized solution for the calculation of in‐air output factors in irregular fields
Authors: Kim Siyong , Palta Jatinder R. , Zhu Timothy C.
Published: July 2002

Three major contributors of scatter radiation to the in‐air output of a medical linear accelerator are the flattening filter, wedge, and tertiary collimator. These were considered separately in the development of an algorithm to be used to set up an in‐air output factor calculation formalism for open and wedge fields of irregular shape. A detector's eye view (DEV) field defined at the source plane was used to account for the effects of collimator exchange and the partial blockage of the flattening filter by the tertiary collimator in the determination of head scatter. An irregular field determined at the source plane by a DEV was segmented and mapped back into the detector plane by a field‐mapping method. Field mapping was performed by using a geometric conversion factor and equivalent field relationships for head scatter. The scatter contribution of each segmented equivalent field at the detector plane was summed by Clarkson integration. The same methodology was applied for determining both tertiary collimator and wedge scatter contribution. However, the field size that determined the amount of scatter contribution was not the same for each component. For tertiary collimator scatter and external wedge scatter, a field projected to the detector plane was used directly. Comparisons of calculated and measured values for in‐air output factors showed good agreement for both open and external wedge fields. This algorithm can also be used for multileaf collimator (MLC) fields irrespective of the position of the MLC (i.e., whether the MLC replaces one secondary collimator or is used as a tertiary collimator). The measurement and parameterization of tertiary collimator scatter is necessary to account for its contribution to the in‐air output. Because a source‐plane field is mapped into the detector plane, no additional dosimetric data acquisition is necessary for the calculation of head scatter.
Contralateral subtraction: A novel technique for detection of asymmetric abnormalities on digital chest radiographs
Authors: Li Qiang , Katsuragawa Shigehiko , Ishida Takayuki , Yoshida Hiroyuki , Tsukuda Shunji , MacMahon Heber , Doi Kunio
Published: July 2002

A novel contralateral subtraction technique has been developed to assist radiologists in the detection of asymmetric abnormalities on a single chest radiograph. With this method, the lateral inclination is first corrected by rotating and shifting the original chest image so that the midline of the thorax is aligned with the vertical centerline of the original chest image. The rotated image is then flipped laterally to produce a reversed “mirror” image. Finally, the mirror image is warped and subtracted from the original image for derivation of the contralateral subtraction image. The three key techniques which are employed in this study are applied successively to the initial contralateral subtraction technique for acquisition of improved subtraction images. One hundred PA chest radiographs, including 50 normals and 50 abnormals, were used as the database for this study. The percentage of chest images, which were rated as being adequate, good, or excellent quality of subtraction images by employing a subjective evaluation method, was improved from 73% to 91% by use of the three key techniques. The contralateral subtraction technique can be used for detection of any asymmetric abnormalities, such as lung nodules, pneumothorax, pneumonia, and emphysema, on a single chest radiograph, and therefore has potential utility in a high proportion of abnormal cases.
Effective thermal conduction model for estimating global warming
Authors: Wolbarst Anthony B.
Published: July 2002

This paper presents a simple way to approximate the dependence of the global mean air temperature at Earth’s surface on the atmospheric concentration of carbon dioxide. It treats the atmosphere as a blanket, the effective thermal conductivity of which is a decreasing function of the amount of CO2 present, and does not involve the details of energy transport. The only data required are the CO2 concentrations at the middle of the nineteenth and the end of the twentieth centuries, and the shift in temperature that has occurred over that time. This elementary, phenomenological energy-balance approach is well suited for undergraduate physics courses to illustrate thermal conduction and radiation, by way of the very interesting and critically important example of greenhouse warming of Earth.
Detection of Gaussian signals in Poisson-modulated interference
Authors: Streit Roy L.
Published: July 2002

Passive broadband detection of target signals by an array of hydrophones in the presence of multiple discrete interferers is analyzed under Gaussian statistics and low signal-to-noise ratio conditions. A nonhomogeneous Poisson-modulated interference process is used to model the ensemble of possible arrival directions of the discrete interferers. Closed-form expressions are derived for the recognition differential of the passive-sonar equation in the presence of Poisson-modulated interference. The interference-compensated recognition differential differs from the classical recognition differential by an additive positive term that depend on the interference-to-noise ratio, the directionality of the Poisson-modulated interference, and the array beam pattern.
Backscattering cross section of a rigid biconic reflector
Authors: Eisler Thomas J.
Published: July 2002

Plane wave incidence on a rigid biconic target is considered. A biconic reflector consists of two cones truncated by planes perpendicular to their axes and joined at their smaller flat faces. The cone angles are allowed to be variable, provided their sum is equal to 90°. The backscattering cross section is expressed in terms of a surface integral of the geometrical acoustics field, which results from incident singly and doubly reflected rays. A saddle-point calculation gives a first-order high-frequency approximation in which the backscattering cross section is proportional to the incident wave number and a function of the angle of incidence, cone angles, and inner and outer radii of the truncated cones. This expression is algebraically complex but easy to implement numerically. Results are presented that exercise the parameters of the problem. An interesting result of the solution is that for fixed outer radii there is a nonzero optimum inner radius for backscattering strength. For broadside incidence on 45° cones with equal outer radii, this optimum value is approximately equal to 11% of the outer radius.
Active control of coupled structural/acoustic intensities in a fluid-loaded elastic plate
Authors: Fischer Matthias , Hayek Sabih I.
Published: July 2002

In this paper, active control of structural intensity and radiated acoustic power in a coupled structure–fluid system is explored. The response of an infinite fluid-loaded plate and the resultant acoustic pressure field are calculated using a hybrid analytic/numerical approach. Two control strategies are examined: (1) the minimization of the total input power, and (2) the minimization of a weighted sum of structural intensity and the radiated acoustic power. Below coincidence, the vibration response of the plate is dominated by nondecaying waves, thus it can be reduced very efficiently by the active control strategies of minimizing the total input power or minimizing the structural intensity. Below coincidence, the acoustic radiation is caused by fast decaying structural waves thus, and active control strategies that aim to minimize the structural intensity have little impact on the radiated pressure field. Furthermore, the control strategy for minimizing the radiated acoustic power does not perform satisfactorily below coincidence since the controllers cannot be coupled to the fast decaying waves. Above coincidence, a slowly decaying structural wave dominates both the plate response and the acoustic radiation, and thus the structural intensity and the radiated acoustic power can be reduced significantly by each of the two control strategies.
A unified boundary element method for the analysis of sound and shell-like structure interactions. II. Efficient solution techniques
Authors: Chen Shaohai , Liu Yijun , Dou Xinyu
Published: July 2002

Efficient solution methods are investigated in this paper for solving the linear system of equations resulting from the recently developed boundary element method (BEM) for the coupled structural acoustic analysis [S. H. Chen and Y. J. Liu, J. Acoust. Soc. Am. 106, Pt. 1, 1247–1254 (1999)]. An iterative solver, namely, the quasiminimal residual method (QMR), is selected among others and found to be very favorable over the direct solver for solving the linear systems of equations with complex coefficients generated by the structural acoustic BEM. Four problem-dependent preconditioning schemes are developed to facilitate or accelerate the convergence of the iterative solver. A new effective preconditioner specially designed for frequency-sweep analysis is also presented in this paper. With this preconditioner, the iterative solver has been found to be stable in a frequency-sweep analysis and can converge much faster than the direct solver. The double-precision arithmetic is also found very useful in improving the convergence rate of the iterative solver for structural acoustic problems.
Effects of sonic booms on breeding gray seals and harbor seals on Sable Island, Canada
Authors: Perry Elizabeth A. , Boness Daryl J. , Insley Stephen J.
Published: July 2002

The Concorde produces audible sonic booms as it passes 15 km north of Sable Island, Nova Scotia, where gray and harbor seals occur year round. The purpose of this research was to assess how sonic booms affect these seals. The intensity of the booms was measured and three types of data (beach counts, frequency of behavior, and heart rate) were collected before and after booms during the breeding seasons of the two species. In addition to the data taken during breeding, beach counts were made before and after booms during the gray seal moult. The greatest range in overpressure within a single boom was 2.70 psf during gray seal breeding and 2.07 psf during harbor seal breeding. No significant differences were found in the behavior or beach counts of gray seals following sonic booms, regardless of the season. Beach counts and most behaviors of harbor seals also did not differ significantly following booms, however, harbor seals became more vigilant. The heart rates of four gray seal mothers and three pups showed no clear change as a result of booms, but six male harbor seals showed a nonsignificant tendency toward elevated heart rates during the 15-s interval of the boom. These results suggest sonic booms produced by the Concorde, in level flight at altitude and producing on average a sonic boom of 0.9 psf, do not substantially affect the breeding behavior of gray or harbor seals.