bluuebunny/crossref_metadata_2025 huggingface dataset:
Shadow monochromatic backlighting: Large-field high resolution
X-ray shadowgraphy with improved spectral tunability
Authors: PIKUZ T.A. , FAENOV A. YA. , FRAENKEL M. , ZIGLER A. , FLORA F. , BOLLANTI S. , DI LAZZARO P. , LETARDI T. , GRILLI A. , PALLADINO L. , TOMASSETTI G. , REALE A. , REALE L. , SCAFATI A. , LIMONGI T. , BONFIGLI F. , ALAINELLI L. , DEL RIO M. SANCHEZ
Published: November 2002

The shadow monochromatic backlighting (SMB) scheme, a modification
of the well-known soft X-ray monochromatic backlighting scheme,
is proposed. It is based on a spherical crystal as the dispersive
element and extends the traditional scheme by allowing one to
work with a wide range of Bragg angles and thus in a wide spectral
range. The advantages of the new scheme are demonstrated
experimentally and supported numerically by ray-tracing
simulations. In the experiments, the X-ray backlighter source
is a laser-produced plasma, created by the interaction of an
ultrashort pulse, Ti:Sapphire laser (120 fs, 3–5 mJ,
1016 W/cm2 on target) or a short wavelength
XeCl laser (10 ns, 1–2 J, 1013 W/cm2 on
target) with various solid targets (Dy, Ni + Cr, BaF2).
In both experiments, the X-ray sources are well localized spatially
(∼20 μm) and are spectrally tunable in a relatively wide
wavelength range (λ = 8–15 Å). High quality monochromatic
(δλ/λ ∼ 10−5–10−3)
images with high spatial resolution (up to ∼4 μm) over a large field
of view (a few square millimeters) were obtained. Utilization
of spherically bent crystals to obtain high-resolution, large
field, monochromatic images in a wide range of Bragg angles
(35° < Θ < 90°) is demonstrated for the first
time.
Studies on nonconventional high-gain target design for ICF
Authors: CARUSO A. , STRANGIO C.
Published: November 2002

This paper reports some of the studies on nonconventional ICF
approaches performed at the ICF Physics and Technology Laboratory
of the AEEF in Frascati, Italy. Having as reference potential
difficulties associated to the conventional central spark ignition
(fuel mixing) and to the usual approach to fast ignition by
laser (transfer and coupling of the energy pulse, fast electrons
energy tuning), we have made explorative work on possible
alternatives. The performances of targets ignited near stagnation
by pulses of heavy ion beams (HIB) or by macroparticle impact
were previously studied. The needed driver energy, the power,
and the beam quality requirements, as well as the level of
synchronization the implosion and the igniting pulse have been
found. More recently, to relax some requirements on the HIB
beam parameters set by the previous approach, the injected entropy
approach (IE) has been introduced. In this method, the conditions
for spark formation are set in the final stages of the implosion,
when the spark fuel size is a few times the final size at
stagnation (volume a few tens of the final). Energy is injected
at this time to set the spark fuel on a high adiabat. In this
paper, for illustration and comparison purposes, some relevant
results we previously obtained for near-stagnation ignition
are first introduced and critically reviewed. The new IE method,
after a short analytical introduction, is presented and illustrated
by the results of extensive 2-D numerical simulations. The
considered cases refer to imploding cylinders of finite length.
As required by this approach, one or two opposing beams axially
injected additional energy, whereas the acceleration stage of
the cylindrical low-entropy implosion was assumed driven by
a different driver. Heavy ion beams, soft X-rays (SXR), and
laser generated light ion beams were considered as vectors for
the entropy injection. Issues related to the feasibility of
these generators are discussed. The study was made for various
initial conditions leading to different ignition modes and burn
propagation. The most recent results on the injected entropy
method to the ignition of high gain targets are included.
Low microdivergence medium-mass ion beam produced from a
N2O cryogenic diode
Authors: KASUYA KOICHI , KISHI YOHSUKE , KAMIYA TAKAHIRO , FUNATSU MASATO
Published: November 2002

Medium-mass ion beams including nitrogen and oxygen were produced
from a cryogenic diode with N2O ice as the ion source.
The nominal diode voltage was 300–400 kV, and the peak
ion current was 240 A. The beam divergence angle was measured
with a five-aperture time-integrated pinhole camera. The five
camera images were analyzed to estimate the spatial distribution
of the beam source divergence angle along the anode radius,
yielding a value of 5–6 mrad for the average microdivergence.
This is low enough for this ion source to be studied further
in the near future. If possible, we want to consider this as
one of the probable candidate ion sources for ion beam drivers
for future inertial confinement fusion (ICF) and inertial fusion
energy (IFE) applications.
Correlated stopping of relativistic electrons in
supercompressed DT fuel
Authors: DEUTSCH C. , FROMY P.
Published: November 2002

On page 303, Equation (15a) needs a correction. The
superscript of Re e … is supposed to have
a plus not a minus (see arrow). Also, following the equations
of (15a), “x = 1” has to be added to the
first line of the text.
Z pinches—A historical view
Authors: SPIELMAN R.B. , DE GROOT J.S.
Published: November 2002

Z pinches have a long and varied history. Beginning
in the 18th century, z pinches have been used to heat
plasmas very efficiently. Early in the nuclear fusion program,
it was realized that modest currents are required to confine
plasma that could produce energy gain. The instability of the
confined plasma was convincingly demonstrated in experiments
in the 1950s that were performed around the world. These uniformly
negative results led to z pinches being dropped as
a fusion concept. Recent progress in fast z pinches
has reinvigorated the field. We review the field and highlight
the recent advances that point the way to a bright future for
z pinches.
Plasma wake-field excitation by relativistic electron bunches
and charged particle acceleration in the presence of external
magnetic field
Authors: BALAKIREV V.A. , KARAS' V.I. , KARAS' I.V. , LEVCHENKO V.D.
Published: November 2002

High-amplitude plasma wake waves are excited by high-density
relativistic electron bunches (REB) moving in a plasma. The
wake-fields can be used to accelerate charged particles, to
serve as electrostatic wigglers in plasma free-electron lasers
(FEL), and also can find many other applications. The
electromagnetic fields in the region occupied by the bunch control
the dynamics of the bunch itself. This paper presents the results
of 2.5-dimensional numerical simulation of the modulation of
a long REB in a plasma, the excitation of wake-fields by bunches
in a plasma, in particular, in magnetoactive plasma. The previous
one-dimensional study has shown that the density-profile modulation
of a long bunch moving in plasma results in the growth of the
coherent wake-wave amplitude. The bunch modulation occurs at
the plasma frequency. The present study is concerned with the
REB motion, taking into account the plasma and REB nonlinearities.
It is demonstrated that the nonlinear REB/plasma dynamics exerts
primary effect on both the REB self-modulation and the wake-field
excitation by the bunches formed. We have demonstrated that a
multiple excess of the accelerated bunch energy εmax
over the energy of the exciting REB is possible in a magnetoactive
plasma for a certain relationship between the parameters of the
“plasma–bunch–magnetic field” system (owing
to a hybrid volume–surface character of REB-excited wake-fields).
Flyer acceleration experiments using a KrF laser system with
a long pulse duration and pressure and thickness of isobaric
zone induced in impacted materials
Authors: KADONO T. , YOSHIDA M. , MITANI N.K. , MATSUMURA T. , TAKAHASHI E. , MATSUSHIMA I. , OWADANO Y. , SASATANI Y. , FUJITA K. , OZAKI N. , TAKAMATSU K. , NAKANO M. , TANAKA K.A. , TAKENAKA H. , ITO H. , KONDO K.
Published: November 2002

Flyer acceleration experiments are carried out using a KrF
laser system with a pulse duration of 10–15 ns and an
intensity of ∼1.0 × 1013 W/cm2.
Three-layered targets (aluminum–polyimide–tantalum)
are used. First, an average velocity of laser-driven tantalum
flyers with a thickness of 4 and 8 μm is estimated. Then,
in a collision of a flyer with a copper layer attached to a
diamond plate, we measure a transit time of a shock wave in
the diamond. The impact velocity is estimated based on the transit
time and a numerical simulation. This numerical simulation also
shows that the initial peak pressure caused by the impact of
a 4-μm-thick flyer is kept at 11 Mbar for 12–13 μm
in thickness. Finally, whether this thickness is enough for
EOS measurements is discussed.
X-ray emission from hollow atoms produced by collisions of
multiply charged ions with a solid
Authors: MORIBAYASHI KENGO , SUTO KEIKO , ZHIDKOV A. , SASAKI AKIRA , KAGAWA TAKASHI
Published: November 2002

The X-ray emission from hollow atoms produced by collisions
of multiply charged ions accelerated by a short pulse laser
with a solid or foil is studied theoretically. The possibility
of obtaining a high conversion efficiency X-ray source in an
ultrafast atomic process (∼1 fs) is demonstrated using the
multistep-capture-and-loss (MSCL) model. Such an X-ray source
has a clear advantage for the spectral range around a few
kiloelectron volts over the conventional Kα
X-ray source. Namely, the number of X-ray photons increases as the
laser energy becomes larger and could reach 3 × 1011
photons for a laser energy of about 10 J.
CO2 laser ion source: Comparison between mode-locked
and free-running laser beams
Authors: LISI N. , MEYER C. , SCRIVENS R.
Published: November 2002

The production of highly charged ions in a CO2
laser-generated plasma is compared for different laser pulse-time
structures. The work was performed at the CERN Laser Ion Source,
which has the aim of developing a high current, high charge-state
ion source for the Large Hadron Collider (LHC). When an intense
laser pulse is focused onto a high-Z metal target,
the ions expanding in the plasma plume are suitable for extraction
from the plasma and matching into a synchrotron. For the first
time, a comparison is made between free-running pulses with
randomly fluctuating intensity, and mode-locked pulse trains
with a reproducible structure and the same energy. Despite the
lower power density with respect to the mode-locked pulse train,
the free-running pulse provides higher charge states and higher
yield.
Editorial
Authors: Miley George H.
Published: November 2002

I deeply regret stepping down from the position as Editor-in-Chief
of Laser and Particle Beams (LPB), but this has become necessary
as my other professional responsibilities have changed.
Fortunately, Dieter Hoffmann is an ideal replacement who will
provide the leadership needed to maintain the quality and continue
the growth of LPB. I am confident that, under his direction,
the journal will continue to serve the scientific community
as a leading vehicle to exchange and archive forefront research
results.The success of LPB to this point has been due to the
work and contributions of many people. I learned much from Heinz
Hora, the founding editor of LPB, during the 4 year overlap
period when I served as Managing Editor. He continued to provide
much help and advice after I took over in 1992. The Associate
Editors and the Editorial Board have also played an instrumental
role in the Journal's operations, ranging from advice about
editorial policies to helping with special issues and with Guest
Editors. The many authors who have submitted such outstanding
manuscripts over the years are, of course, the fundamental reason
the journal is so well received in the community. The various
reviewers who have given so much time to their work have been
integral to maintaining the journal quality. Last, but not least,
thanks goes to the Cambridge University Press staff who have
so ably handled the proofing, printing and circulation of the
Journal.
The prospect of laser fusion in the 21st century
Authors: YAMANAKA CHIYOE
Published: November 2002

Inertial confinement fusion (ICF) has developed remarkably
in the last 30 years. In the 21st century, we can expect fusion
energy for civilian use. After the cold war era, the value of
ICF has shifted from defense demands to peaceful applications.
The megajoule laser systems are under construction expecting
the development of spark ignition. However there are many problems
to solve in science and technology. One alternative way is to
use a petawatt short-pulse laser aiming for fast ignition. On
the way to the final goal, we would like to contribute for various
applications of high power lasers such as laboratory astrophysics,
X-ray lasers, laser-induced lightning as well as laser processing.
Rapid fuel layering inside moving free-standing ICF targets:
Physical model and simulation code development
Authors: ALEKSANDROVA I.V. , BAZDENKOV S.V. , CHTCHERBAKOV V.I.
Published: November 2002

In this report, we discuss the physical concept and the results
of mathematical modeling of free-standing target (FST) layering
for inertial confinement fusion (ICF), including the detailed
descriptions of the heat transfer and layer symmetrization mechanisms.
Propagation issues and energetic particle production in
laser–plasma interactions at intensities exceeding
1019 W/cm2
Authors: BORGHESI M. , CAMPBELL D.H. , SCHIAVI A. , WILLI O. , GALIMBERTI M. , GIZZI L.A. , MACKINNON A.J. , SNAVELY R.D. , PATEL P. , HATCHETT S. , KEY M. , NAZAROV W.
Published: November 2002

A series of experiments recently carried out at the Rutherford
Appleton Laboratory investigated various aspects of the
laser–plasma interaction in the relativistic intensity
regime. The propagation of laser pulses through preformed plasmas
was studied at intensities exceeding 1019 W/cm2.
The transmission of laser energy through long-scale underdense plasmas
showed to be inefficient unless a plasma channel is preformed ahead of
the main laser pulse. The study of the interaction with overdense plasmas
yielded indication of collimated energy transport through the plasma. The
production of fast particles during the interaction with solid density
targets was also investigated. The measurements revealed the presence of
a small-sized directional source of multi-megaelectron volt protons, which
was not observed when a plasma was preformed at the back of the solid target.
The properties of the source are promising in view of its use in radiographic
imaging of dense matter, and preliminary tests were carried out.
Development of an X-ray photoelectron microscopic system
with a compact X-ray source
Authors: FUJIKAWA CHIEMI , YAMAGUCHI NAOHIRO , OHCHI TADAYUKI , HARA TAMIO , WATANABE KATSUMI , TANAKA IBUKI , TAGUCHI MASAMI
Published: November 2002

We have constructed an X-ray photoelectron microscopic system.
An X-ray source is a laser-produced plasma in a scheme of an
X-ray laser experiment. X rays involving amplified spontaneous
emissions (ASE) at 15.47 nm were delivered with a 10-Hz repetition
rate from a compact X-ray laser system. X rays were collected
and focused by a Schwarzschild optics coated with Mo/Si multilayers
for a 15.47-nm X ray. Photoelectron signals due to the Ga
3d and As 3d electrons were observed, when
a GaAs wafer was used as a sample. The spatial resolution of
about 1 μm was confirmed.
Line X-ray emission from Al targets irradiated by
high-intensity, variable-length laser pulses
Authors: LIMPOUCH J. , RENNER O. , KROUSKÝ E. , USCHMANN I. , FÖRSTER E. , KALASHNIKOV M.P. , NICKLES P.V.
Published: November 2002

The absolutely calibrated K-shell spectra emitted from
short-living aluminum plasmas at laser intensities of 5 ×
1015–4 × 1018 W/cm2
are reported. The experiments performed with the constant energy,
variable-length laser pulses (1.5 ps–1 ns) are modeled by the
one-dimensional (1D) hydrodynamics code, including nonlinear resonance
absorption of the laser radiation, fast electron acceleration, and
energy transfer into the target. The characteristic features of the
measured and the postprocessed spectra are outlined. The spatial
and temporal profiles of the emitted spectra are presented;
the scaling rules for the conversion efficiency of the laser
radiation into the line X-ray emission are discussed.
Femtosecond, picosecond, and nanosecond laser microablation:
Laser plasma and crater investigation
Authors: SEMEROK A. , SALLÉ B. , WAGNER J.-F. , PETITE G.
Published: November 2002

Crater shapes and plasma plume expansion in the interaction
of sharply focused laser beams (10 μm waist diameter, 60
fs–6 ns pulse duration) with metals in air at atmospheric
pressure were studied. Laser ablation efficiencies and rates
of plasma expansion were determined. The best ablation efficiency
was observed with femtosecond laser pulses. It was found that
for nanosecond pulses, the laser beam absorption, its scattering,
and its reflection in plasma were the limiting factors for
efficient laser ablation and precise material sampling with
sharply focused laser beams. The experimental results obtained
were analyzed with relation to different theoretical models
of laser ablation.
Transverse structures in corona of nonuniformly irradiated
solid targets
Authors: LIMPOUCH J. , ISKAKOV A.B. , MAšEK K. , ROHLENA K. , LEBO I.G. , TISHKIN V.F.
Published: November 2002

Formation of transverse inhomogeneities in the corona of a
solid target irradiated by an inhomogeneous main laser pulse
and a uniform background pulse was observed experimentally via
side-on shadowgraphy. The experimental results were successfully
interpreted using a two-dimensional hydrodynamics code. Our
simulations identified the onset of sharp contact boundaries
between plasma streams of different expansion velocities. The
formation and the decay of the contact boundaries is investigated
in detail. When the background pulse is used as a laser prepulse,
a layer of coronal plasma is formed that enhances main pulse
collisional absorption in underdense plasma and creates conditions
for an efficient thermal smoothing of the transverse inhomogeneities.
Energy spectra of Ag, Au, Sn, and Pb ions emitted from
laser-created plasmas determined from their implantation depth
profile in a metallic substrate
Authors: KRÁSA JOSEF , LÁSKA LEOš , ROHLENA KAREL , PEŘINA VRATISLAV , HNATOWICZ VLADIMÍR
Published: November 2002

The energy spectra of heavy ions emitted from laser-produced
plasmas were determined by the use of a technique relying on
the implantation of plasma ions into a substrate located close
to the plasma. Ion energy spectra were reconstructed from depth
profiles of the implanted ions measured by the standard Rutherford
back-scattering (RBS) technique employing 2 MeV alpha particles
scattered at 170° laboratory angle. The energy spectra of
Ag, Au, Sn, and Pb ions, implanted into aluminum or steel foils,
are presented. A review of other techniques for ion energy spectrum
measurement is presented and their limitations are discussed.
The hard X-ray continuum from intense ultrashort KrF
laser–solid interaction
Authors: TAO Y.Z. , WANG N.Y. , SHAN Y.S. , LI Y.J. , TANG X.Z. , ZHANG H.F.
Published: November 2002

The hard X-ray (>30 keV) continuum from the interaction
of a Ti:sapphire/KrF intense femtosecond UV laser (50 mJ, 440
fs, 10 Hz at 248 nm) with a solid has been measured; the intensity
on the target is up to 1017 W/cm2. The X-ray
with energy of 200 keV has been observed; the temperature of the
hot electron from fitting the spectrum utilizing Maxwellian
distribution is 67 keV. This is the first measurement of hard
X-rays from femtosecond KrF laser–solid interaction.
Fast calculation of plasma prominent atomic magnitudes by
using a new analytical potential for excited configurations
Authors: RODRÍGUEZ R. , RUBIANO J.G. , GIL J.M. , MARTEL P. , MÍNGUEZ E.
Published: November 2002

In this work, a new analytical potential for studying ions
in excited configurations is presented, which is built up from
a parametric potential for ions in a ground state. It is used
to calculate atomic magnitudes of special importance in plasmas
such as total energies, energy levels, and transition energies,
for ions in excited configurations. The results are successfully
compared with those obtained with both self-consistent or
analytical models.
Calculation of the ionization state for LTE plasmas using
a new relativistic-screened hydrogenic model based on analytical
potentials
Authors: RUBIANO J.G. , RODRÍGUEZ R. , GIL J.M. , MARTEL P. , MÍNGUEZ E.
Published: November 2002

In this work, the Saha equation is solved using atomic data
provided by means of a new relativistic-screened hydrogenic
model based on analytical potentials to calculate the ionization
state and ion abundance for LTE iron plasmas. The plasma effects
on the atomic structure are taken into account by including
the classical continuum lowering correction of Stewart and Pyatt.
For high density, the Saha equation is modified to consider
the degeneration of free electrons using the Fermi–Dirac
statistics instead of the Maxwellian distribution commonly used.
The results are compared with more sophisticated self-consistent
codes.
Application of solitons to the study of laser propagation
into a thermonuclear plasma in inertial confinement fusion
Authors: BLAZQUEZ J.F. MIRAMAR
Published: November 2002

In this work, we study the laser propagation in a thermonuclear
plasma corresponding to implosion of deuterium-tritium pellets
in inertial confinement fusion, by injecting energy provided
by high-power laser devices into a quiescent plasma and generating
solitons. Having in mind that the electric field inside of plasma
can be studied by means of a particular non-linear Schrödinger
equation, we solve this equation as an inverse problem, using
the Inverse Scattering Transform method, that is a 2 ×
2 eigenvalue problem, known as the AKNS scheme, developed by
Ablovitz, Kamp, Newell, and Shabat. We obtain the pseudopotentials
q and r if we suppose that the eigenvalue
is invariant in time, and is representative of a wave eigenvector,
obtaining a solution that has a structure of the soliton type.
In the process, one change of variable for space and another
for time are applied, and the relation between the pseudopotentials
is given by r = −q*. Discretization
of the non-linear Schrödinger equation, solved by inverse scattering
transform are given by Ablovitz et al. (1999). These solitons
are generated near the critical layer where w0
≅ wp, w0 being the
laser frequency and wp the plasma frequency,
exhibit a change in electronic density profile and are caused
by the ponderomotive force of laser radiation.
A TANDEM FLUID QUEUE WITH GRADUAL INPUT
Authors: Scheinhardt Werner R.W. , Zwart Bert
Published: November 2002

For a two-node tandem fluid model with gradual input, we compute
the joint steady-state buffer-content distribution. Our proof
exploits martingale methods developed by Kella and Whitt. For
the case of finite buffers, we use an insightful sample-path
argument to extend an earlier proportionality result of Zwart
to the network case.
BOUNDS AND PERFORMANCE LIMITS OF CHANNEL ASSIGNMENT POLICIES
IN CELLULAR NETWORKS
Authors: Bäuerle Nicole , Houdek Anja
Published: November 2002

We investigate the performance of channel assignment policies
for cellular networks. The networks are given by an interference
graph which describes the reuse constraints for the channels.
In the first part, we derive lower bounds on the expected
(weighted) number of blocked calls under any channel assignment
policy over finite time intervals as well as in the average
case. The lower bounds are solutions of deterministic control
problems. As far as the average case is concerned, the control
problem can be replaced by a linear program. In the second part,
we consider the cellular network in the limit, when the number
of available channels as well as the arrival intensities are
linearly increased. We show that the network obeys a functional
law of large numbers and that a fixed channel assignment policy
which can be computed from a linear program is asymptotically
optimal. Special networks like fully connected and star networks
are considered.
ON A STOCHASTIC INVENTORY MODEL WITH DETERIORATION AND
STOCK-DEPENDENT DEMAND ITEMS
Authors: Benkherouf Lakdere , Aggoun Lakhdar
Published: November 2002

In this article, we propose a new continuous-time stochastic
inventory model with deterioration and stock-dependent demand
items. We then formulate the problem of finding the optimal
impulse control schedule that minimizes the total expected return
over an infinite horizon, as a quasivariational inequality (QVI)
problem. The QVI is shown to lead to an (s, S)
policy, where s and S are determined uniquely as
a solution of some algebraic equations.
CONDUCTIVITY OF RANDOM TREES
Authors: Konsowa Mokhtar H.
Published: November 2002

We prove that the effective resistances of spherically symmetric
random trees dominate in mean the effective resistances of random
trees corresponding branching processes in varying environments
and having the same growth law of spherically symmetric trees.
We conjecture that the statement does not necessarily hold true
in the case of stochastic domination and give an idea of
constructing a counterexample.
ON THE STRUCTURE OF THE SPACE OF GEOMETRIC PRODUCT-FORM MODELS
Authors: Bayer Nimrod , Boucherie Richard J.
Published: November 2002

This article deals with Markovian models defined on a
finite-dimensional discrete state space and possess a stationary
state distribution of a product-form. We view the space of such
models as a mathematical object and explore its structure.
We focus on models on an orthant
[script Z]+n, which are homogeneous within
subsets of [script Z]+n called walls, and
permit only state transitions whose ∥ ∥∞-length
is 1. The main finding is that the space of such models exhibits a
decoupling principle: In order to produce a given product-form
distribution, the transition rates on distinct walls of the same
dimension can be selected without mutual interference. This principle
holds also for state spaces with multiple corners (e.g., bounded boxes in
[script Z]+n).

In addition, we consider models which are homogeneous throughout
a finite-dimensional grid [script Z]n, now without
a fixed restriction on the length of the transitions. We characterize
the collection of product-form measures which are invariant for a model
of this kind. For such models with bounded transitions, we prove, using
Choquet's theorem, that the only possible invariant measures are
product-form measures and their combinations.
OPTIMAL CONTROL OF PARALLEL QUEUES WITH BATCH SERVICE
Authors: Xia Cathy H. , Michailidis George , Bambos Nicholas , Glynn Peter W.
Published: November 2002

We consider the problem of dynamic allocation of a single server
with batch processing capability to a set of parallel
queues. Jobs from different classes cannot be processed together
in the same batch. The arrival processes are mutually independent
Poisson flows with equal rates. Batches have independent and
identically distributed exponentially distributed service times,
independent of the batch size and the arrival processes. It
is shown that for the case of infinite buffers, allocating the
server to the longest queue, stochastically maximizes the aggregate
throughput of the system. For the case of equal-size finite
buffers the same policy stochastically minimizes the loss of
jobs due to buffer overflows. Finally, for the case of
unequal-size buffers, a threshold-type policy is
identified through an extensive simulation study and shown to
consistently outperform other conventional policies. The good
performance of the proposed threshold policy is confirmed in
the heavy-traffic regime using a fluid model.
OPTIMAL MAINTENANCE AND OPERATION OF A SYSTEM WITH BACKUP
COMPONENTS
Authors: Righter Rhonda
Published: November 2002

We consider a system with heterogeneous unreliable components
that requires only one component to be turned on in order for
it to operate. Repair workers may have different skills and
may be unavailable for random periods of time. The problem is
to determine a usage and repair policy to maximize system
availability. We give conditions under which the optimal usage
policy is to always use, or turn on, the component with the
shortest repair time, and the optimal repair policy is to always
repair the most reliable component (with the smallest failure
rate). We fully characterize the optimal policy when there are
only two components. Our system is equivalent to a closed system
with multiple single-server queues, where the objective is to
minimize server idle time at one of the queues.
ON THE CONVERGENCE OF METROPOLIS-TYPE RELAXATION AND ANNEALING
WITH CONSTRAINTS
Authors: Robini Marc C. , Bresler Yoram , Magnin Isabelle E.
Published: November 2002

We discuss the asymptotic behavior of time-inhomogeneous
Metropolis chains for solving constrained sampling and optimization
problems. In addition to the usual inverse temperature schedule
(βn)n∈[hollow
N]*, the type of Markov processes under consideration
is controlled by a divergent sequence
(θn)n∈[hollow N]*
of parameters acting as Lagrange multipliers. The associated transition
probability matrices
(Pβn,θn)n∈[hollow N]*
are defined by Pβ,θ =
q(x,
y)exp(−β(Wθ(y)
− Wθ(x))+) for
all pairs (x, y) of distinct elements of a finite set
Ω, where q is an irreducible and reversible Markov kernel
and the energy function Wθ is of the form
Wθ = U + θV for
some functions U,V : Ω → [hollow R].
Our approach, which is based on a comparison of the distribution
of the chain at time n with the invariant measure of
Pβn,θn, requires the computation of an upper bound for the
second largest eigenvalue in absolute value of Pβn,θn.
We extend the geometric bounds derived by Ingrassia and we give
new sufficient conditions on the control sequences for the
algorithm to simulate a Gibbs distribution with energy U
on the constrained set [Ω with tilde above] = {x ∈
Ω : V(x) = minz∈ΩV(z)} and to minimize U over [Ω with
tilde above].
The expression of pragmatic values by means of verbal
morphology: A variationist study
Authors: Pollán Celia
Published: November 2002

In this article we identify a variable context in the use of
two Galician verb forms (cantei and cantara)
and three Spanish verb forms used in Galicia
(canté, cantara, and había
cantado) with identical modal, temporal, and aspectual
values: the simple past indicative. We show that the variation
in question is constrained by linguistic factors, specifically
pragmatic ones, and that, although the forms cantei
and canté are widely preferred, contexts with
low discourse focalization favor cantara and
había cantado. Finally, we test this hypothesis
with data from two language corpora (Galician and Galician
Spanish), which are quantified and interpreted with the program
VARBRUL 2S.
Negative concord in the Old and New World: Evidence from Scotland
Authors: Smith Jennifer
Published: November 2002

In this article, I conduct a quantitative analysis of negative
concord in Buckie, a relic dialect from the northeast of Scotland,
and compare these findings with transported varieties of English
in North America. Two major results arise from the analysis.
First, Buckie has high rates of use of negative concord to
indeterminates within the same clause, as do all the dialects
included in the study. Second, negative concord in other
environments is found in certain varieties in the New World
that have no counterparts in the Old World. I suggest that the
quantitative similarities can be explained in terms of the
primitive status of negative concord in vernacular varieties
of English, in combination with a shared linguistic heritage
during the colonial period. The qualitative differences demonstrate
that contexts of linguistic heterogeneity in North America during
the early colonization period led to an extension and restructuring
of the original rules.
Why worser is better: The double comparative in
16th- to 17th-century English
Authors: Schlüter Julia
Published: November 2002

In Early Modern English, double comparatives were often
encountered in both spoken and written language. The present
article investigates the redundantly marked comparative
worser in relation to its irregular, but etymologically
justified, counterpart worse. My aim is to examine
the diachronic development of the form as well as its distribution
in the written language of the 16th and 17th centuries. Two
detailed corpus studies are used to reveal the set of parameters
underlying the variation between worse and
worser, which include system congruity, semantics,
and standardization effects. However, the focus here is on the
tendency to maintain an alternation of stressed and unstressed
syllables, known as the Principle of Rhythmic Alternation. This
prosodic principle (which has been argued to be particularly
influential in English) turns out to be responsible for most
of the results obtained in the analysis of the corpus data.
Lexical diffusion as a factor of phonetic change: The case
of Modern French nasal vowels
Authors: Hansen Anita Berit
Published: November 2002

The present study explores the notion of lexical diffusion
in relation to an ongoing change in Modern French nasal vowels.
Data are interviews with 42 Parisians, recorded in 1972–74
and 1989–93. We start with the notion that sound change
ought to be regular, according to the classification of Labov
(1994): that is, being a phonetically gradual change, it should
be lexically abrupt. The first part of our analysis, which includes
more than 10,000 nasal vowel tokens, seems to indicate an influence
of factors compatible with the hypothesis of regular sound change
(i.e., stress and phonetic surroundings). A closer look at the
vowel /[vowel symbol]/, however, reveals an independent lexical and
grammatical conditioning, one not entirely explicable in terms
of stress or phonetics. As other studies have shown (Krishnamurti,
1998; Yaeger-Dror, 1996), gradual phonetic change might show
lexical irregularities, a fact which calls for a revision of
Labov's classification.
TRANSITIONAL DYNAMICS AND THRESHOLDS IN ROMER'S ENDOGENOUS TECHNOLOGICAL CHANGE MODEL
Authors: Garcia-Castrillo Pedro , Sanso Marcos
Published: November 2002

We obtain the transitional dynamics of the decentralized economy described by P.M. Romer and characterize the dynamic behavior of the most relevant variables. We determine the existence of a stable one-dimensional manifold containing a steady state with innovation, unique in ratios, and also find a threshold in the accumulation of physical capital below which the economy is not innovating. Finally, using simulations, we assess the significance of this threshold and analyze the influence that technological and utility parameters have on it.
PRIVATIZATION TRANSFERS AND CREDIT MARKET FRICTIONS
Authors: Chun Rodney M.
Published: November 2002

This paper examines an economy in which output is produced by state-owned enterprises and private firms. Private-capital formation requires intermediation that is subject to a credit market friction. In this environment, I look at the effects of a privatization policy that transfers state-owned capital to the private sector. Multiple steady-state equilibria are possible. When these arise, the low-wage equilibrium features a relatively inefficient financial system and privatization transfers help to increase the aggregate capital stock by reducing the severity of the credit market frictions. On the other hand, privatization transfers may have adverse effects when the economy is at the high-wage equilibrium. Analysis of the dynamic characteristics of the model reveals that development trap phenomenon and endogenous fluctuations can be observed.
SEASONALITY, PRODUCTIVITY SHOCKS, AND SECTORAL COMOVEMENTS IN A REAL BUSINESS CYCLE MODEL FOR ITALY
Authors: Cubadda Gianluca , Savio Giovanni , Zelli Roberto
Published: November 2002

This paper investigates the degree of comovements in quarterly Italian time series of sectoral output. A recently developed multivariate technique for the empirical analysis of long-run, cyclical and seasonal comovements is used in the context of a multisectoral real-business-cycle model augmented with persistent seasonal shocks in productivity. Our empirical results emphasize the role of input–output relations in the propagation mechanism and indicate that sectoral outputs have a relatively low number of common stochastic trends, in conflict with the hypothesis of independent productivity shocks. In contrast, stochastic seasonals seem to move idiosyncratically. Furthermore, our findings suggest that the theoretical model should be extended to allow for deterministic seasonal shifts in preferences.
ROBUST MONETARY POLICY UNDER MODEL UNCERTAINTY IN A SMALL MODEL OF THE U.S. ECONOMY
Authors: Onatski Alexei , Stock James H.
Published: November 2002

This paper examines monetary policy in a two-equation macroeconomic model when the policymaker recognizes that the model is an approximation and is uncertain about the quality of that approximation. It is argued that the minimax approach of robust control provides a general and tractable alternative to the conventional Bayesian decision theoretic approach. Robust control techniques are used to construct robust monetary policies. In most (but not all) cases, these robust policies are more aggressive than the optimal policies absent model uncertainty. The specific robust policies depend strongly on the formulation of model uncertainty used, and we make some suggestions about which formulation is most relevant for monetary policy applications.
ROBUST DECISION THEORY AND THE LUCAS CRITIQUE
Authors: Marcellino Massimiliano , Salmon Mark
Published: November 2002

In this paper, we reconsider the theoretical basis for the Lucas critique from the point of view of robust decision theory. We first emphasize that the Lucas critique rests on a weak theoretical paradigm in that it fails to consider the motivation for the policy change by the government and hence inconsistently assumes limited rationality by the government. When placed in a proper dynamic general equilibrium framework of a dynamic game between the government and the private sector, much of the force of the critique simply vanishes. We also reconsider the critique by adopting an alternative theoretical paradigm and notion of rationality based on robust decision theory. This view of rationality might be regarded as more relevant than the nonrobust rationality employed by Lucas and, critically, it is one in which the Lucas critique can be shown simply not to apply, provided the private sector has adopted suitably robust decision rules.
DYNAMICS OF TAXES, PUBLIC SERVICES, AND ENDOGENOUS GROWTH
Authors: Park Hyun , Philippopoulos Apostolis
Published: November 2002

We present a model of endogenous growth in which government consumption and production services are financed by distorting capital taxes. We generalize Barro's public finance model of growth in two ways. First, we study the properties, and the role in growth, of a wider menu of second-best optimal policies, namely, the capital tax rate and the portion of total tax revenues used to finance public production services versus public consumption services. Second, we investigate the possibility of the existence and uniqueness of a long-run equilibrium in which optimal policies do not change and the economy grows at a constant balanced growth path, as well as the possibility of dynamic determinacy of this long-run equilibrium.
A lysophosphatidic acid analogue is revealed as a potent inhibitor of phosphatidylcholine synthesis, inducing apoptosis
Authors: GUEGUEN Geneviéve , GRANCI Virginie , ROGALLE Pierre , BRIAND-MÉSANGE Fabienne , WILSON Michéle , KLAÉBÉ Alain , TERCÉ François , CHAP Hugues , SALLES Jean-Pierre , SIMON Marie-Françoise , GAITS Frédérique
Published: November 2002

A previous study demonstrated that cross-desensitization experiments performed with the lysophosphatidic acid (LPA) analogues (R)- and (S)-N-palmitoyl-norleucinol 1-phosphate (PNPAs) inhibited LPA-induced platelet aggregation without any stereospecificity. Here we report opposite biological effects of the two enantiomers on mitogenesis of IMR-90 fibroblasts in relation to their respective metabolism. (R)PNPA was proliferative, while (S)PNPA induced apoptosis by specifically inhibiting phosphatidylcholine biosynthesis at the last step of the CDP-choline pathway controlled by cholinephosphotransferase. This effect was not direct but required dephosphorylation of PNPAs by ecto-lipid phosphate phosphatase before cellular uptake of the generated N-palmitoyl-norleucinols (PNOHs). Inhibition of cholinephosphotransferase by the derivative (S)PNOH was confirmed by an in vitro assay. (S)PNPA proapoptotic effects led us to clarify the mechanism linking cholinephosphotransferase inhibition to apoptosis. Three proapoptotic responses were observed: the activation of caspase-3, the production of ceramides from newly synthesized pools (as demonstrated by the inhibitor Fumonisin B1) and finally the activation of stress-activated protein kinase, p38 and c-Jun N-terminal kinases 1/2, as a result of ceramide increase. Thus our data demonstrate that synthetic analogues of LPA might display stereospecific effects leading to apoptosis independently of classical LPA-activated pathways.
Transcriptional regulation of the rat type IIA phospholipase A2 gene by cAMP and interleukin-1β in vascular smooth muscle cells: interplay of the CCAAT/enhancer binding protein (C/EBP), nuclear factor-κB and Ets transcription factors
Authors: ANTONIO Valérie , BROUILLET Arthur , JANVIER Brigitte , MONNE Claire , BEREZIAT Gilbert , ANDREANI Marise , RAYMONDJEAN Michel
Published: November 2002

The abundant secretion of type IIA secreted phospholipase A2 (sPLA2) is a major feature of the inflammatory process of atherosclerosis. sPLA2 is crucial for the development of inflammation, as it catalyses the production of lipid mediators and induces the proliferation of smooth muscle cells. We have analysed the activation of sPLA2 transcription by cAMP and interleukin-1β (IL-1β), and shown that the 500bp region upstream of the transcription start site of the rat sPLA2 gene is implicated in activation by synergistically acting cAMP and IL-1β. We transiently transfected and stimulated rat smooth muscle cells in primary culture and measured the promoter activities of serial and site-directed deletion mutants of sPLA2—luciferase constructs. A distal region, between −488 and −157 bp, bearing a CAAT/enhancer binding protein (C/EBP)-responsive element (-242 to −223) was sufficient for cAMP/protein kinase A-mediated sPLA2 promoter activation. We find evidence for the first time that activation of the sPLA2 promoter by IL-1β requires activation of an Ets-responsive element in the −184 to −180 region of the distal promoter via the Ras pathway and a nuclear factor-κB site at positions −141 to −131 of the proximal promoter. We also used electrophoretic mobility shift assays to identify five binding sites for the Sp1 factor; a specific inhibitor of Sp1, mithramycin A, showed that this factor is crucial for the basal activity of the sPLA2 promoter.
Interactions between two fission yeast serine/arginine-rich proteins and their modulation by phosphorylation
Authors: TANG Zhaohua , KÄUFER Norbert F. , LIN Ren-Jang
Published: November 2002

The unexpected low number of genes in the human genome has triggered increasing attention to alternative pre-mRNA splicing, and serine/arginine-rich (SR) proteins have been correlated with the complex alternative splicing that is a characteristic of metazoans. SR proteins interact with RNA and splicing protein factors, and they also undergo reversible phosphorylation, thereby regulating constitutive and alternative splicing in mammals and Drosophila. However, it is not clear whether the features of SR proteins and alternative splicing are present in simple and genetically tractable organisms, such as yeasts. In the present study, we show that the SR-like proteins Srp1 and Srp2, found in the fission yeast Schizosaccharomyces pombe, interact with each other and the interaction is modulated by protein phosphorylation. By using Srp1 as bait in a yeast two-hybrid analysis, we specifically isolated Srp2 from a random screen. This Srp interaction was confirmed by a glutathione-S-transferase pull-down assay. We also found that the Srp1—Srp2 complex was phosphorylated at a reduced efficiency by a fission yeast SR-specific kinase, Dis1-suppression kinase (Dsk1). Conversely, Dsk1-mediated phosphorylation inhibited the formation of the Srp complex. These findings offer the first example in fission yeast for interactions between SR-related proteins and the modulation of the interactions by specific protein phosphorylation, suggesting that a mammalian-like SR protein function may exist in fission yeast.
Ionizing radiation induces ataxia telangiectasia mutated kinase (ATM)-mediated phosphorylation of LKB1/STK11 at Thr-366
Authors: SAPKOTA Gopal P. , DEAK Maria , KIELOCH Agnieszka , MORRICE Nick , GOODARZI Aaron A. , SMYTHE Carl , SHILOH Yosef , LEES-MILLER Susan P. , ALESSI Dario R.
Published: November 2002

The serine/threonine protein kinase LKB1 functions as a tumour suppressor, and mutations in this enzyme lead to the inherited Peutz—Jeghers cancer syndrome. We previously found that LKB1 was phosphorylated at Thr-366 in vivo, a residue conserved in mammalian, Xenopus and Drosophila LKB1, located on a C-terminal non-catalytic moiety of the enzyme. Mutation of Thr-366 to Ala or Asp partially inhibited the ability of LKB1 to suppress growth of G361 melanoma cells, but did not affect LKB1 activity in vitro or LKB1 localization in vivo. As a first step in exploring the role of this phosphorylation further, we have generated a phosphospecific antibody specifically recognizing LKB1 phosphorylated at Thr-366 and demonstrate that exposure of cells to ionizing radiation (IR) induced a marked phosphorylation of LKB1 at Thr-366 in the nucleus. Thr-366 lies in an optimal phosphorylation motif for the phosphoinositide 3-kinase-like kinases DNA-dependent protein kinase (DNA-PK), ataxia telangiectasia mutated kinase (ATM) and ataxia telangiectasia-related kinase (ATR), which function as sensors for DNA damage in cells and mediate cellular responses to DNA damage. We demonstrate that both DNA-PK and ATM efficiently phosphorylate LKB1 at Thr-366 in vitro and provide evidence that ATM mediates this phosphorylation in vivo. This is based on the finding that LKB1 is not phosphorylated in a cell line lacking ATM in response to IR, and that agents which induce cellular responses via ATR in preference to ATM poorly induce phosphorylation of LKB1 at Thr-366. These observations provide the first link between ATM and LKB1 and suggest that ATM could regulate LKB1.
Recent Neutron Investigations on Biomolecular Dynamics: From Model Systems towards Complex Macromolecular Machines
Authors: Deriu Antonio , Natali Francesca
Published: November 2002

Neutron high resolution spectroscopic studies of biomolecular dynamics have been pursued actively in the last decade. They probe macromolecular thermal dynamics in a space-time window of about 1–10 Å and 10–1000 ps, which is involved in biological activity, because this window corresponds to the motions of H-atoms bound to larger groups such as the amino acid side chains. As a result of advances in instrumentation and data analysis methods, it is nowadays possible to obtain quantitative information on the complex low frequency motions exhibited by biologically active systems. In the near future, the advent of new sources and the availability of dedicated instruments will make it possible to extend these studies from “pure” systems, like single proteins, towards more complex ones as protein–lipid and protein–DNA complexes, glyco-lipid systems, ribosomes and even whole cells. Some selected examples highlighting possible future research areas will be illustrated.