bluuebunny/crossref_metadata_2025 huggingface dataset:
Robustness of the Ewens sampling formula
Authors: Joyce Paul
Published: April 2006

Under the assumptions of the neutral infinite alleles model,K(the total number of alleles present in a sample) is sufficient for estimatingθ(the mutation rate). This is a direct result of the Ewens sampling formula, which gives a consistent, asymptotically normal estimator forθbased onK. It is shown that the same estimator used to estimateθunder neutrality is consistent and asymptotically normal, even when the assumption of selective neutrality is violated.
On the asymptotic distribution of the maximum number of infectives in epidemic models by immigration
Authors: Abramov V. M.
Published: April 2006

This paper considers the asymptotic distribution of the maximum number of infectives in an epidemic model by showing that, as the initial number of susceptibles converges to infinity, the process of infectives converges almost surely to a birth and death process. The model studied here is more general than usual (see e.g. Bailey (1975), Bharucha-Reid (1960), Keilson (1979)) in that it incorporates immigration and the limiting birth and death process is non-linear. The main novelty of the present paper is the martingale approach used to prove the above-mentioned convergence.
Moment bounds for non-stationary dependent sequences
Authors: Kim Tae Yoon
Published: April 2006

We provide a unified approach for establishing even-moment bounds for partial sums for a class of weakly dependent random variables satisfying a stationarity condition. As applications, we discuss moment bounds for various types of mixing sequences. To obtain even-moment bounds, we use a ‘combinatorial argument' developed by Cox and Kim (1990).
Lundberg bounds on the tails of compound distributions
Authors: Willmot Gordon E. , Lin Xiaodong
Published: April 2006

Exponential bounds are derived for the tail probabilities of various compound distributions, generalizing the classical Lundberg inequality of insurance risk theory. Failure rate properties of the compounding distribution including log-convexity and log-concavity are considered in some detail. Mixed Poisson compounding distributions are also considered. A ruin theoretic generalization of the Lundberg inequality is obtained in the case where the number of claims process is a mixed Poisson process. An application to the M/G/1 queue length distribution is given.
Comments on the Luria–Delbrück distribution
Authors: Kemp Adrienne W.
Published: April 2006

The long-tailed Luria–Delbrück distribution arises in connection with the ‘random mutation’ hypothesis (whereas the ‘directed adaptation' hypothesis is thought to give a Poisson distribution). At timetthe distribution depends on the parameterm=gNt/(a+g) whereNtis the current population size andg/(a+g) is the relative mutation rate (assumed constant). The paper identifies three models for the distribution in the existing literature and gives a fourth model. Ma et al. (1992) recently proved that there is a remarkably simple recursion relation for the Luria–Delbrück probabilitiespnand found that asymptoticallypn≈c/n2; their numerical studies suggested thatc= 1 when the parametermis unity. Cairns et al. (1988) had previously argued and shown numerically that Pn= Σj ≧ nPj≈ m/n. Here we prove thatn(n+ 1)pn< m(1 + 11m/30) forn= 1, 2, ···, and hence prove that asnbecomes largen(n+ 1)pn, ≈m; the resultmPn≈mfollows immediately.
The Mk/G/∞ batch arrival queue by heterogeneous dependent demands
Authors: Falin Gennadi
Published: April 2006

Choi and Park [2] derived an expression for the joint stationary distribution of the number of customers of k types who arrive in batches at an infinite-server system of M/M/∞ type. We propose another method of solving this problem and extend the result to the case of general service times (not necessarily independent). We also get a transient solution. Our main result states that the k- dimensional vector of the number of customers of k types in the system is a certain linear function of a (2k – 1)-dimensional vector whose coordinates are independent Poisson random variables.
Boundary crossing probability for Brownian motion and general boundaries
Authors: Wang Liqun , Pötzelberger Klaus
Published: April 2006

An explicit formula for the probability that a Brownian motion crosses a piecewise linear boundary in a finite time interval is derived. This formula is used to obtain approximations to the crossing probabilities for general boundaries which are the uniform limits of piecewise linear functions. The rules for assessing the accuracies of the approximations are given. The calculations of the crossing probabilities are easily carried out through Monte Carlo methods. Some numerical examples are provided.
Braess's paradox in a queueing network with state-dependent routing
Authors: Calvert Bruce , Solomon Wiremu , Ziedins Ilze
Published: April 2006

We consider initially two parallel routes, each of two queues in tandem, with arriving customers choosing the route giving them the shortest expected time in the system, given the queue lengths at the customer's time of arrival. All interarrival and service times are exponential.

We then augment this network to obtain a Wheatstone bridge, in which customers may cross from one route to the other between queues, again choosing the route giving the shortest expected time in the system, given the queue lengths ahead of them.

We find that Braess's paradox can occur: namely in equilibrium the expected transit time in the augmented network, for some service rates, can be greater than in the initial network.
Tandem queues with bulk arrivals, infinitely many servers and correlated service times
Authors: Sumita Ushio , Masuda Yasushi
Published: April 2006

A system of GIx/G/∞ queues in tandem is considered where the service times of a customer are correlated but the service time vectors for customers are independently and identically distributed. It is shown that the binomial moments of the joint occupancy distribution can be generated by a sequence of renewal equations. The distribution of the joint occupancy level is then expressed in terms of the binomial moments. Numerical experiments for a two-station tandem queueing system demonstrate a somewhat counterintuitive result that the transient covariance of the joint occupancy level decreases as the covariance of the service times increases. It is also shown that the analysis is valid for a network of GIx/SM/∞ queues.
The extremal index and clustering of high values for derived stationary sequences
Authors: Weissman Ishay , Cohen Uri
Published: April 2006

Given a sequence of independent identically distributed random variables, we derive a moving-maximum sequence (with random translations). The extremal index of the derived sequence is computed and the limiting behaviour of clusters of high values is studied. We are then given two or more independent stationary sequences whose extremal indices are known. We derive a new stationary sequence by taking either a pointwise maximum or by a mixture of the original sequences. In each case, we compute the extremal index of the derived sequence.
Some comparison results for multitype epidemic models
Authors: Clancy Damian
Published: April 2006

We consider a model for the spread of an epidemic through a population divided intomgroups, in which infectives move from group to group and infect only within their current group. For both deterministic and stochastic versions of this model, the effect on the total size of the epidemic of varying the speed with which infectives move between groups is considered. We also compare the distribution of the total size of this model with that of a suitably matched model in which infectives cannot move between groups, but are able to infect outside their own group.
On the arc-sine laws for Lévy processes
Authors: Getoor R. K. , Sharpe M. J.
Published: April 2006

LetXbe a Lévy process on the real line, and letFcdenote the generalized arcsine law on [0, 1] with parameterc. Thent−1⨍0tP0(Xs> 0)ds→cast →∞ is a necessary and sufficient condition fort—1⨍0t1{Xs>0}dsto converge inP0law toFc.Moreover,P0(Xt> 0)= cfor allt >0 is a necessary and sufficient condition fort—1⨍0t1{Xs>0}dsunderP0to have lawFcfor allt> 0. We give an elementary proof of these results, and show how to derive Spitzer's theorem for random walks in a simple way from the Lévy process version.
Multivariate self-similar processes: second-order theory
Authors: Bladt M.
Published: April 2006

The aim of this paper is to extend the existing theory of second-order self-similar processes as defined by Cox (1984) from the univariate case to higher dimensions. Multivariate self-similar processes defined in terms of second-order theory for stationary time series can be used as models for long-range dependent observations when the marginal observations are long-range dependent. An interesting question concerns the correlation structure within the processes when the marginal processes are correlated. We show that the self-similarity requirement, as defined in this article, implies a cross-correlation structure similar to that for the marginal processes. This occurs both in the time domain and in the frequency domain. This fact can be used to obtain generalized least squares estimates for the long-range dependence parameters. We discuss some difficulties concerning estimation based on simulations.
The variance of a truncated mixed exponential process
Authors: Hebert Jaimie L. , Seaman John W.
Published: April 2006

Mullooly (1988) provides sufficient conditions under which the variance of a left-truncated, non-negative random variable will be greater than the variance of the original variable. We consider this problem for the class of exponential mixtures, and provide an explicit expression for the inflation in variance in terms of the mixing density.
On a best-choice problem by dependent criteria
Authors: Gnedin Alexander V.
Published: April 2006

We study the problem of maximizing the probability of stopping at an object which is best in at least one of a given set of criteria, using only stopping rules based on the knowledge of whether the current object is relatively best in each of the criteria. The asymptotic results for the case of independent criteria are shown to hold in certain cases where the componentwise maxima are, pairwise, either asymptotically independent or asymptotically full dependent.

An example of the former is a random sample from a bivariate correlated normal distribution; thus our results settle a question posed recently by T. S. Ferguson.
A generalization of ‘expectation equals reciprocal of intensity' to non-stationary exponential distributions
Authors: Feinberg Eugene A.
Published: April 2006

An observer watches one of a set of Poisson streams. He may switch from one stream to another instantaneously. If an arrival occurs in a stream while the observer is watching another stream, he does not see the arrival. The experiment terminates when the observer sees an arrival. We derive a formula which states essentially that the expected total time that the observer watches a stream is equal to the probability that he sees the arrival in this stream divided by the intensity of the stream. This formula is valid independently of the observation policy. We also discuss applications of this formula.
Multivariate normal approximations by Stein's method and size bias couplings
Authors: Goldstein Larry , Rinott Yosef
Published: April 2006

Stein's method is used to obtain two theorems on multivariate normal approximation. Our main theorem, Theorem 1.2, provides a bound on the distance to normality for any non-negative random vector. Theorem 1.2 requires multivariate size bias coupling, which we discuss in studying the approximation of distributions of sums of dependent random vectors. In the univariate case, we briefly illustrate this approach for certain sums of nonlinear functions of multivariate normal variables. As a second illustration, we show that the multivariate distribution counting the number of vertices with given degrees in certain random graphs is asymptotically multivariate normal and obtain a bound on the rate of convergence. Both examples demonstrate that this approach may be suitable for situations involving non-local dependence. We also present Theorem 1.4 for sums of vectors having a local type of dependence. We apply this theorem to obtain a multivariate normal approximation for the distribution of the random p-vector, which counts the number of edges in a fixed graph both of whose vertices have the same given color when each vertex is colored by one of p colors independently. All normal approximation results presented here do not require an ordering of the summands related to the dependence structure. This is in contrast to hypotheses of classical central limit theorems and examples, which involve for example, martingale, Markov chain or various mixing assumptions.
Increasing the reliability of a machine reduces the period of its work
Authors: Sonin Isaac M.
Published: April 2006

The comparison of optimal strategies in a simple stochastic replacement model for two types of machines with identical cost characteristics when one of them is more reliable than the other is conducted. It is proven that the scheduled replacement period for the more reliable type is always less than for the less reliable one. An example is presented when even the expected period of use of a more reliable machine is less than the expected period for the less reliable one. Some related problems are briefly discussed.
Asymptotic analysis of queueing systems with identical service
Authors: Karpelevitch F. I. , Kreinin A. Ya.
Published: April 2006

We consider a heavy traffic regime in queueing systems with identical service. These systems belong to the class of multi-phase systems with dependent service times in different service nodes. We study the limit behaviour of the waiting time vector in heavy traffic. Both transient behaviour and the stationary regime are considered. Our analysis is based on the conception of ‘approximated functionals', which appeared to be fruitful in weak convergence theory of stochastic processes.
On a symmetry-based constructive approach to probability densities for two-dimensional diffusion processes
Authors: Di Crescenzo A. G. , Giorno V. , Nobile A. G. , Ricciardi L. M.
Published: April 2006

The method earlier introduced for one-dimensional diffusion processes [6] is extended to obtain closed form expressions for the transition p.d.f.'s of two-dimensional diffusion processes in the presence of absorbing boundaries and for the first-crossing time p.d.f.'s through such boundaries. Use of such a method is finally made to analyse a two-dimensional linear process.
Persistence of a critical super-2 process
Authors: Gorostiza Luis G. , Hochberg Kenneth J. , Wakolbinger Anton
Published: April 2006

It is shown that the critical two-level (2,d, 1, 1)-superprocess is persistent in dimensionsdgreater than 4. This complements the extinction result of Wu (1994) and implies that the critical dimension is 4.
Inspection times for stand-by units
Authors: Parmigiani Giovanni
Published: April 2006

This paper studies optimal timing of inspections for units in cold stand-by. The problem is approached in continuous time. The policies developed adapt optimally to information provided by failures of the main unit and by ageing of both the standby and the main unit.

Results include a general form for the optimal policy, consisting of a recursive relation between successive inspection times, and of a renewal-type integral equation to determine the value of the objective function for a given policy. Further results are derived for the case in which the failure densities describing the process are logconcave. Then the stopping rule is easily characterized. It is also shown that the interval between inspections decreases with time, and that the optimal schedule is unique. A binary search algorithm for finding the solution is outlined.
Servers in tandem with k-stage blocking and communications-type flow
Authors: Avi-Itzhak Benjamin
Published: April 2006

Modeling of manufacturing lines and data communications makes frequent use of tandem queues with blocking. Here we present and study such a system with a k-stage blocking scheme in which processing in each station requires attendance of the server of that station together with the servers of the next k – 1 stations. This scheme describes the conventional manufacturing and communications blocking schemes but is also representative of a wider range of applications. Explicit expressions for residence times, throughput, queueing times, waiting times and other measures of performance are obtained for the case of communications type flow and just-in-time input. Use of the results in modeling and analyzing a highway traffic flow situation is presented.
Classes of life distributions and renewal counting process
Authors: Chen Yi-Hau
Published: April 2006

We prove that if the renewal function M(t) corresponding to a life distribution F is convex (concave) then F is NBU (NWU), and hence answer two questions posed by Shaked and Zhu (1992). Moreover, based-on the renewal function, some characterizations of the exponential distribution within certain classes of life distributions are given.
Isolation of Intestinal Brush‐Border Membranes
Authors: Cheeseman Chris I , O'Neill Debbie
Published: April 2006

This unit provides protocols for isolating intestinal brush‐border membranes from rat, pig, and cow. These membranes can be used for immunoblotting or other analytical techniques. They will also spontaneously form closed vesicles which allow for flux assays to be performed using rapid filtration techniques. Overall the isolation procedures take ∼3.5 hr. The resulting isolated membranes can be stored under liquid nitrogen or at −70°C for a week or more depending upon the species.
Isolation and Characterization of Exosomes from Cell Culture Supernatants and Biological Fluids
Authors: Théry Clotilde , Amigorena Sebastian , Raposo Graça , Clayton Aled
Published: April 2006

Exosomes are small membrane vesicles found in cell culture supernatants and in different biological fluids. Exosomes form in a particular population of endosomes, called multivesicular bodies (MVBs), by inward budding into the lumen of the compartment. Upon fusion of MVBs with the plasma membrane, these internal vesicles are secreted. Exosomes possess a defined set of membrane and cytosolic proteins. The physiological function of exosomes is still a matter of debate, but increasing results in various experimental systems suggest their involvement in multiple biological processes. Because both cell‐culture supernatants and biological fluids contain different types of lipid membranes, it is critical to perform high‐quality exosome purification. This unit describes different approaches for exosome purification from various sources, and discusses methods to evaluate the purity and homogeneity of the purified exosome preparations.
Assessing vertical resolution requirements for operational weather radar data quality
Authors: Mittermaier Marion P. , Illingworth Anthony J. , Hogan Robin J.
Published: April 2006

High‐resolution, 0.28° beamwidth range‐height‐indicator (RHI) data are used to simulate the reflectivities measured at various ranges by an operational radar with a 1° beamwidth. It is found that the sampling is optimal when the elevation increments equal the beamwidth. Larger increments lead to an unacceptable loss of information. Copyright © 2006 Royal Meteorological Society
Increased expression of nuclear factor E2 p45‐related factor 2 (NRF2) in head and neck squamous cell carcinomas
Authors: Stacy Donnie R. , Ely Kim , Massion Pierre P. , Yarbrough Wendell G. , Hallahan Dennis E. , Sekhar Konjeti R. , Freeman Michael L.
Published: April 2006

Background.

Head and neck squamous cell carcinoma (HNSCC) continues to cause significant morbidity and mortality. Overexpression of specific phase II gene products may represent an important biomarker. One regulator of phase II gene expression is the transcription factor nuclear factor E2 p45‐related factor 2 (Nrf2). Nrf2 expression was evaluated in HNSCC, to determine whether it might serve as a biomarker for early detection of disease.

Methods.

A tissue microarray was constructed of 141 HNSCC biopsy cores from 47 HNSCCs. In addition, histologically normal squamous mucosa was obtained from 7 patients. Protein expression was evaluated by immunohistochemistry.

Results.

Nrf2 expression was increased in 91.5% of tumors. Expression of thioredoxin, a Nrf2‐reguated gene product, was elevated in 75% of tumors. Keap1, which regulates the rate of Nrf2 ubiquitination and degradation, was relatively overexpressed in HNSCC compared with normal mucosa.

Conclusions.

Nrf2 expression may be a possible HNSCC candidate biomarker. © 2006 Wiley Periodicals, Inc. Head Neck, 2006
The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure?
Authors: Verstraeten Gert , Poesen Jean , Gillijns Katleen , Govers Gerard
Published: April 2006

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.
Macroporous and nanofibrous polymer scaffolds and polymer/bone‐like apatite composite scaffolds generated by sugar spheres
Authors: Wei Guobao , Ma Peter X.
Published: April 2006

Scaffolds are crucial to tissue engineering/regeneration. In this work, a technique combining a unique phase‐separation process with a novel sugar sphere template leaching process has been developed to produce three‐dimensional scaffolds. The resulting scaffolds possess high porosities, well connected macropores, and nanofibrous pore walls. The technique advantageously controls macropore shape and size by sugar spheres, interpore opening size by assembly conditions (time and temperature of heat treatment), and pore wall morphology by phase‐separation parameters. The bioactivity of a macroporous and nanofibrous poly(L‐lactic acid) (PLLA) scaffold was demonstrated by the bone‐like apatite deposition throughout the scaffold in a simulated body fluid (SBF). Preincorporation of nanosized hydroxyapatite eliminated the induction period and facilitated the apatite growth in the SBF. Interestingly, the apatite growth primarily occurred on the surface of the pores (internal and external) but not the interior of the nanofibrous network away from the pore surface. It was also noticed that the macropore size did not affect the apatite growth rate, while the interpore opening size did. The compressive modulus also increased substantially when a continuous apatite layer was formed on the pore walls of the scaffold. The resulting composite scaffold mimics natural bone matrix with the combination of an organic phase (a polymer such as PLLA) and an inorganic apatite phase. The demonstrated bioactivity of apatite layer, together with well‐controlled macroporous and nanofibrous structures, makes the novel nanocomposite scaffolds desirable for bone tissue engineering. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Copolymers containing a spiro orthoester moiety that undergo no shrinkage during cationic crosslinking
Authors: Kume Makoto , Hirano Atsunori , Ochiai Bungo , Endo Takeshi
Published: April 2006

A spiro orthoester with an exomethylene group (exoSOE) was radically copolymerized with acrylonitrile or vinyl acetate at several feed ratios to obtain the corresponding copolymers having spiro orthoester moieties in the side chain. The obtained copolymers could be crosslinked via the double ring‐opening polymerization of the spiro orthoester moieties in their side chain by a treatment with BF3OEt2. The volume changes upon the crosslinking of the copolymers were evaluated by density measurements with a micromeritics gas pycnometer. The copolymers experienced less than 1% volume expansion instead of volume shrinkage during typical cationic crosslinking, regardless of the copolymer compositions. Negligible shrinkage was observed during the thermal cationic crosslinking of a film cast from a nitrobenzene solution of the copolymers containing a benzylthiophenium salt as a thermally latent cationic initiator. The constantly low volume changes during the crosslinking of the copolymers from exoSOE probably depended on the almost zero volume change during the cationic polymerizations of spiro orthoester derivatives. This indicates that exoSOE is an effective monomer for crosslinkable polymers without volume changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3666–3673, 2006
A multidimensional scaling analysis of the techniques that physiotherapists use
Authors: Turner Patricia A , Whitfield T W Allan
Published: April 2006

Following the essentially ‘hands‐on’ origin of the physiotherapy profession a century ago, the range of techniques available to practitioners has expanded considerably. While this expansion of techniques has been of research interest, the main focus has been upon individual techniques, thus neglecting the fundamental question of the use of techniques in combination. In addition, researchers have tended to treat the profession as homogeneous, thus overlooking possible differences in technique usage. Copyright © 1997 Whurr Publishers Ltd.
Manipulation and four‐probe analysis of nanowires in UHV by application of four tunneling microscope tips: a new method for the investigation of electrical transport through nanowires
Authors: Lin Xiao , He Xiaobo , Lu Junling , Gao Li , Huan Qing , Deng Zhitao , Cheng Zhihai , Shi Dongxia , Gao Hongjun
Published: April 2006

The electrical transport properties of nanosystems, including a few kinds of nanowires, have attracted much attention because of their potential application in nanoelectronics. However, the contact effect or impurities between the nanosystems and electrodes made it difficult to study the intrinsic I–V properties in previous measurements. Here, we present a manipulation and four‐terminal method electrical transport measurement of low‐dimensional systems using a new instrument consisting of a specially designed tunneling microscope with four tips that can be positioned independently in three dimensions. The electrical conductivities of zinc oxide (ZnO), perylene, gallium sesquioxide (Ga2O3), and cuprum‐7,7′,8,8′‐tetracyanoquinodimethane (Cu‐TCNQ) nanowires were obtained. Our results have shown that this technique is a powerful tool for studying the intrinsic transport properties of nanosystems. Copyright © 2006 John Wiley & Sons, Ltd.
Nanodissection, isolation, and PCR amplification of single DNA molecules
Authors: Lü Junhong , An Hongjie , Li Haikuo , Li Xueling , Wang Ying , Li Minqian , Zhang Yi , Hu Jun
Published: April 2006

A unique technique for positioning, dissection, and isolation of single DNA molecules using atomic force microscopy (AFM) has been demonstrated. Full‐length genome DNA molecules were first deposited and stretched by a modified ‘Molecular Combing’ technique on a 3‐aminopropyl triethoxysilane‐coated mica substrate. A single DNA fragment was dissected from individual genome DNA strands with the AFM tip at the desired position, and then isolated (or picked up) after a special operation called ‘kneading’. All the operations including imaging, dissection, and isolation could be carried out with one tip. The isolated DNA fragment on the AFM tip could be successfully amplified by single‐molecule PCR. Some of the physical and chemical mechanisms are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
A poset hierarchy
Authors: Džamonja Mirna , Thompson Katherine
Published: April 2006

This article extends a paper of Abraham and Bonnet which generalised the famous Hausdorff characterisation of the class of scattered linear orders. They gave an inductively defined hierarchy that characterised the class of scattered posets which do not have infinite incomparability antichains (i.e. have the FAC). We define a larger inductive hierarchy κℌ* which characterises the closure of the class of all κ-well-founded linear orders under inversions, lexicographic sums and FAC weakenings. This includes a broader class of “scattered” posets that we call κ-scattered. These posets cannot embed any order such that for every two subsets of size < κ, one being strictly less than the other, there is an element in between. If a linear order has this property and has size κ it is unique and called ℚ(κ). Partial orders such that for every a < b the set {x: a < x < b} has size ≥ κ are called weakly κ-dense, and posets that do not have a weakly κ-dense subset are called strongly κ-scattered. We prove that κℌ* includes all strongly κ-scattered FAC posets and is included in the class of all FAC κ-scattered posets. For κ = ℵ0 the notions of scattered and strongly scattered coincide and our hierarchy is exactly aug(ℌ) from the Abraham-Bonnet theorem.
Accurate potential energy surface and quantum reaction rate calculations for the H+CH4→H2+CH3 reaction
Authors: Wu Tao , Werner Hans-Joachim , Manthe Uwe
Published: April 2006

Calculations for the cumulative reaction probability N(E) (for J=0) and the thermal rate constant k(T) of the H+CH4→H2+CH3 reaction are presented. Accurate electronic structure calculations and a converged Shepard-interpolation approach are used to construct a potential energy surface which is specifically designed to allow the precise calculation of k(T) and N(E). Accurate quantum dynamics calculations employing flux correlation functions and multiconfigurational time-dependent Hartree wave packet propagation compute N(E) and k(T) based on this potential energy surface. The present work describes in detail the various convergence test performed to investigate the accuracy of the calculations at each step. These tests demonstrate the predictive power of the present calculations. In addition, approximate approaches for reaction rate calculations are discussed. A quite accurate approximation can be obtained from a potential energy surface which includes only interpolation points on the minimum energy path.
On the Euler angles for SU(N)
Authors: Bertini Stefano , Cacciatori Sergio L. , Cerchiai Bianca L.
Published: April 2006

In this paper we reconsider the problem of the Euler parametrization for the unitary groups. After constructing the generic group element in terms of generalized angles, we compute the invariant measure on SU(N) and then we determine the full range of the parameters, using both topological and geometrical methods. In particular, we show that the given parametrization realizes the group SU(N+1) as a fibration of U(N) over the complex projective space CPn. This justifies the interpretation of the parameters as generalized Euler angles.
Frequency chirping for resonance-enhanced electron energy during laser acceleration
Authors: Gupta D. N. , Suk H.
Published: April 2006

The model given by Singh-Tripathi [Phys. Plasmas 11, 743 (2004)] for laser electron acceleration in a magnetic wiggler is revisited by including the effect of laser frequency chirping. Laser frequency chirp helps to maintain the resonance condition longer, which increases the electron energy gain. A significant enhancement in electron energy gain during laser acceleration is observed.
Lysosomal biogenesis and function is critical for necrotic cell death in Caenorhabditis elegans
Authors: Artal-Sanz Marta , Samara Chrysanthi , Syntichaki Popi , Tavernarakis Nektarios
Published: April 2006

Necrotic cell death is defined by distinctive morphological characteristics that are displayed by dying cells (Walker, N.I., B.V. Harmon, G.C. Gobe, and J.F. Kerr. 1988. Methods Achiev. Exp. Pathol. 13:18–54). The cellular events that transpire during necrosis to generate these necrotic traits are poorly understood. Recent studies in the nematode Caenorhabditis elegans show that cytoplasmic acidification develops during necrosis and is required for cell death (Syntichaki, P., C. Samara, and N. Tavernarakis. 2005. Curr. Biol. 15:1249–1254). However, the origin of cytoplasmic acidification remains elusive. We show that the alkalization of endosomal and lysosomal compartments ameliorates necrotic cell death triggered by diverse stimuli. In addition, mutations in genes that result in altered lysosomal biogenesis and function markedly affect neuronal necrosis. We used a genetically encoded fluorescent marker to follow lysosome fate during neurodegeneration in vivo. Strikingly, we found that lysosomes fuse and localize exclusively around a swollen nucleus. In the advanced stages of cell death, the nucleus condenses and migrates toward the periphery of the cell, whereas green fluorescent protein–labeled lysosomal membranes fade, indicating lysosomal rupture. Our findings demonstrate a prominent role for lysosomes in cellular destruction during necrotic cell death, which is likely conserved in metazoans.
CAR-1 and Trailer hitch: driving mRNP granule function at the ER?
Authors: Decker Carolyn J. , Parker Roy
Published: April 2006

The targeting of messenger RNAs (mRNAs) to specific subcellular sites for local translation plays an important role in diverse cellular and developmental processes in eukaryotes, including axis formation, cell fate determination, spindle pole regulation, cell motility, and neuronal synaptic plasticity. Recently, a new conserved class of Lsm proteins, the Scd6 family, has been implicated in controlling mRNA function. Depletion or mutation of members of the Scd6 family, Caenorhabditis elegans CAR-1 and Drosophila melanogaster trailer hitch, lead to a variety of developmental phenotypes, which in some cases can be linked to alterations in the endoplasmic reticulum (ER). Scd6/Lsm proteins are RNA binding proteins and are found in RNP complexes associated with translational control of mRNAs, and these complexes can colocalize with the ER. These findings raise the possibility that localization and translational regulation of mRNAs at the ER plays a role in controlling the organization of this organelle.
An illustrative case and a review on the dosing of recombinant factor VIIa in congenital factor XI deficiency
Authors: SCHULMAN S. , NÉMETH G.
Published: April 2006

Summary.  Recombinant activated factor VII (rFVIIa) has been used in a very limited number of patients with severe factor XI (FXI) deficiency. The dose and duration of treatment has varied greatly between these case reports. In a few of these cases there was also evidence of thrombotic complications. We present here a report on one additional patient with congenital FXI deficiency. For two major orthopaedic procedures in this patient we used rFVIIa as a single bolus dose followed by continuous infusion at a low rate. The data from these treatment episodes, together with those from a review of the published cases, lend support to the concept of using much lower doses than in haemophilia with inhibitors. A bolus dose of 20 μg kg−1 and thereafter maintenance of the FVII activity at approximately 3 IU mL−1 appears effective and safe.
Commentary: How can we make our medical students enthusiastic about a future in obstetrics and gynaecology?
Authors: Higham J
Published: April 2006

Falling recruitment to obstetrics and gynaecology (O&G) among UK‐trained undergraduates is a pressing concern. The reasons for this are multifactorial and include the previous restriction on the number of postgraduate training places. Undergraduate placements are a key time to encourage potential recruits into the specialty. A recent survey demonstrated various changes within medical school attachments over the past 15 years that are having a mixed influence on the undergraduate O&G experience. These are explored in relation to their potential impact on recruitment.
Financial Ties between DSM-IV Panel Members and the Pharmaceutical Industry
Authors: Cosgrove Lisa , Krimsky Sheldon , Vijayaraghavan Manisha , Schneider Lisa
Published: April 2006

Background: Increasing attention has been given to the transparency of potential conflicts of interest in clinical medicine and biomedical sciences, particularly in journal publishing and science advisory panels. The authors examined the degree and type of financial ties to the pharmaceutical industry of panel members responsible for revisions of the Diagnostic and Statistical Manual of Mental Disorders(DSM). Methods: By using multimodal screening techniques the authors investigated the financial ties to the pharmaceutical industry of 170 panel members who contributed to the diagnostic criteria produced for the DSM-IV and the DSM-IV-TR. Results: Of the 170 DSM panel members 95 (56%) had one or more financial associations with companies in the pharmaceutical industry. One hundred percent of the members of the panels on ‘Mood Disorders’ and ‘Schizophrenia and Other Psychotic Disorders’ had financial ties to drug companies. The leading categories of financial interest held by panel members were research funding (42%), consultancies (22%) and speakers bureau (16%). Conclusions: Our inquiry into the relationships between DSM panel members and the pharmaceutical industry demonstrates that there are strong financial ties between the industry and those who are responsible for developing and modifying the diagnostic criteria for mental illness. The connections are especially strong in those diagnostic areas where drugs are the first line of treatment for mental disorders. Full disclosure by DSM panel members of their financial relationships with for-profit entities that manufacture drugs used in the treatment of mental illness is recommended.
Smoking as a Risk Factor for Renal Injury in Essential Hypertension
Authors: Tylicki Leszek , Puttinger Heidemarie , Rutkowski Przemyslaw , Rutkowski Boleslaw , Hörl Walter H.
Published: April 2006

Background: Smoking is an important player in the pathogenesis of hypertensive nephropathy. To shed more light on this issue, we performed a case-control cross-sectional study and stratification analyses to evaluate the influence of smoking on surrogate markers of kidney injury and oxidative stress in patients supposed to have hypertensive nephropathy. The dependence of kidney lesions on the ‘extent’ of smoking was determined as well. Methods: 82 patients with essential hypertension and micro- or macro-albuminuria were recruited. The control group consisted of 41 sex- and age-matched healthy individuals. Urine albumin creatinine ratio and plasma von Willebrand factor activity were analysed as markers of endothelial injury. N-acetyl-β-D-glucosaminidase, transforming growth factor-β1 and 15-isoprostane F2t urine excretions were regarded as markers of tubular dysfunction, renal fibrosis and oxidative stress, respectively. Patients’ smoking habits were recorded and categorized on the basis of a self-administered questionnaire. Results: In multivariate regression analysis, the independent associations between smoking and urine albumin (p < 0.05; β = 0.27), von Willebrand factor activity (p < 0.05; β = 0.29) and urine isoprostanes (p < 0.05; β = 0.28) were found. When the smokers were stratified according to the number of cigarettes smoked per day and the time from which they started smoking, ‘heavy smokers’ and ‘long-term smokers’ presented with higher albumin excretion and higher von Willebrand factor activity than ‘light smokers’ and ‘short-term smokers’, respectively. The passive smokers had numerically higher albumin excretion and von Willebrand factor activity than nonsmokers. Conclusion: The study showed that smoking induces oxidative stress. Smoking was also found to be a strong predictor for the extent of endothelial injury in patients with hypertensive kidney injury. Subjects who smoke heavily and for a long time, as well as passive smokers, seem to be particularly exposed to endothelial damage.
Troponin I Testing in Dialysis Patients Presenting to the Emergency Room: Does Troponin I Predict the 30-Day Outcome?
Authors: Bueti Joe , Krahn John , Karpinski Martin , Bohm Clara , Fine Adrian , Rigatto Claudio
Published: April 2006

Background: Troponins are often measured in acutely ill chronic dialysis patients admitted to the emergency room, irrespective of their clinical presentation. The significance of an elevated troponin level in this setting is unclear. Methods: We identified all chronic dialysis patients presenting over 1 year to a tertiary care hospital emergency room who also had at least one cardiac troponin I (cTnI) level determination. We evaluated presenting complaints, risk factors for cardiac disease, cTnI levels, and major cardiac events (MCE; occurrence of cardiovascular death, myocardial infarction, de novo heart failure, or coronary revascularization) within 30 days by chart review in 149 patients (79 on hemodialysis, 70 on peritoneal dialysis). Results: Chest pain was documented in only 29% of the patients. Twenty-two patients (15%) experienced an MCE. The incidence of an MCE was the same in patients with and without chest pain. A cTnI level >0.1 ng/l was a significant predictor of an MCE (odds ratio 15.2, 95% confidence interval CI 5.26, 43.6). The likelihood ratios for MCEs were 0.32 (CI 0.16, 0.63) for a cTnI level <0.1 ng/l, 0.72 (CI 0.09, 5.5) for cTnI concentrations 0.1–0.3 ng/l, 7.8 (CI 4.2, 15) for a cTnI level >0.3, and 11.7 (CI 4.4, 31) for a cTnI concentration >2.0 ng/l. Conclusion: In acutely ill chronic dialysis patients presenting to a hospital emergency room, an elevated cTnI level indicates an increased 30-day cardiac risk, regardless of their clinical presentation.
Endobronchial Embolization with a Silicone Spigot as a Temporary Treatment for Massive Hemoptysis
Authors: Dutau Hervé , Palot Alain , Haas Andrew , Decamps Isabelle , Durieux Olivier
Published: April 2006

A 39-year-old-woman was treated successfully by a combination of endobronchial and bronchial artery embolization for massive hemorrhage originating from the posterior segment of the right upper lobe. Endobronchial embolization was performed using a silicone spigot placed via flexible bronchoscopy in order to prevent alveolar inundation preceding and during the time of bronchial artery embolization. Massive hemorrhage is a rare and severe condition associated with a high mortality that requires rapid intervention and management. We describe a case that emphasizes the efficacy of a multidisciplinary approach including the use of a new bronchoscopic technique.
Using MODIS and AERONET to Determine GCM Aerosol Size
Authors: Lesins Glen , Lohmann Ulrike
Published: April 2006

Aerosol size is still a poorly constrained quantity in general circulation models (GCMs). By using the modal radii of the coarse and fine mode retrieved from 103 stations in the Aerosol Robotic Network (AERONET) and the fine mode aerosol optical depth fraction derived from both the Moderate Resolute Imaging Spectroradiometer (MODIS) Terra and AERONET, a globally and monthly averaged aerosol size distribution dataset was computed assuming internally mixed aerosols. Different methods were employed in creating the size distribution datasets that were input to the ECHAM4 climate model giving a globally averaged aerosol optical depth (AOD) at 500 nm that ranged from 0.11 to 0.20 depending on the method. This translates into a globally averaged direct aerosol top-of-atmosphere forcing range from −1.6 to −3.9 W m−2. Reducing the uncertainty in the aerosol sizes is important when using AOD to validate models since mass burden errors can then be assumed to be the main AOD error source. This paper explores a procedure that can help achieve this goal.
Transit-Time Distributions in a Global Ocean Model
Authors: Peacock Synte , Maltrud Mathew
Published: April 2006

Results from a simulation of the ocean “transit-time distribution” (“TTD”) for global and regional ocean surface boundary conditions are presented based on a 5000-yr integration using the Parallel Ocean Program ocean general circulation model. The TTD describes the probability that water at a given interior point in the ocean was at some point on the ocean surface a given amount of time ago. It is shown that the spatial distribution of ocean TTDs can be understood in terms of conventional wisdom regarding time scales and pathways of the ventilated thermocline and the thermohaline circulation–driven deep-ocean circulation. The true mean age from the model (the first moment of the TTD) is demonstrated to be very large everywhere, because of very long-tailed distributions. Regional TTD distributions are presented for distinct surface boundary subregions, and it is shown how these can help in the interpretation of the global TTD. The spatial structure of each regional TTD is shown to become essentially the same at relatively long times. The form of the TTD at a given point in the ocean can be very simple, but some regions do exhibit more complicated multimodal distributions. The degree to which a simple functional approximation to the TTD is able to predict the spatial and temporal evolution of selected idealized tracers (for which interior sources and sinks are known or zero) with knowledge of only the tracer surface boundary condition is explored.
The Operational JMA Nonhydrostatic Mesoscale Model
Authors: Saito Kazuo , Fujita Tsukasa , Yamada Yoshinori , Ishida Jun-ichi , Kumagai Yukihiro , Aranami Kohei , Ohmori Shiro , Nagasawa Ryoji , Kumagai Saori , Muroi Chiashi , Kato Teruyuki , Eito Hisaki , Yamazaki Yosuke
Published: April 2006

An operational nonhydrostatic mesoscale model has been developed by the Numerical Prediction Division (NPD) of the Japan Meteorological Agency (JMA) in partnership with the Meteorological Research Institute (MRI). The model is based on the MRI/NPD unified nonhydrostatic model (MRI/NPD-NHM), while several modifications have been made for operational numerical weather prediction with a horizontal resolution of 10 km. A fourth-order advection scheme considering staggered grid configuration is implemented. The buoyancy term is directly evaluated from density perturbation. A time-splitting scheme for advection has been developed, where the low-order (second order) part of advection is modified in the latter half of the leapfrog time integration. Physical processes have also been revised, especially in the convective parameterization and PBL schemes. A turbulent kinetic energy (TKE) diagnostic scheme has been developed to overcome problems that arise to predict TKE. The model performance for mesoscale NWP has been verified by comparison with a former operational hydrostatic mesoscale model of JMA. It is found that the new nonhydrostatic mesoscale model outperforms the hydrostatic model in the prediction of synoptic fields and quantitative precipitation forecasts.
Teachers as Exemplars
Authors: Stewart Douglas J.
Published: April 2006

In previous eras, teacher training institutions included programs designed to enhance the moral qualities of prospective teachers. With the exception of programs offered in denominational teacher training colleges, such programs have largely ceased to exist. This article advances the argument against a backdrop of increasing incidents of abuse of students by teachers that there is a need to again place greater emphasis on the moral development of teachers.