bluuebunny/crossref_metadata_2025 huggingface dataset:
Indirect comparison of interventions using published randomised trials: systematic review of PDE-5 inhibitors for erectile dysfunction
Authors: Moore R Andrew , Derry Sheena , McQuay Henry J
Published: December 2005

Background

There are no randomised and properly blinded trials directly comparing one PDE-5 inhibitor with another in a normal home setting. Valid indirect comparisons with a common comparator must examine equivalent doses, similar duration, similar populations, with the same outcomes reported in the same way.

Methods

Published randomised, double-blind trials of oral PDE-5 inhibitors for erectile dysfunction were sought from reference lists in previous reviews and electronic searching. Analyses of efficacy and harm were carried out for each treatment, and results compared where there was a common comparator and consistency of outcome reporting, using equivalent doses.

Results

Analysis was limited by differential reporting of outcomes. Sildenafil trials were clinically and geographically more diverse. Tadalafil and vardenafil trials tended to use enriched enrolment. Using all trials, the three interventions were similar for consistently reported efficacy outcomes. Rates of successful intercourse for sildenafil, tadalafil and vardenafil were 65%, 62%, and 59%, with placebo rates of 23–28%. The rates of improved erections were 76%, 75% and 71%, respectively, with placebo rates of 22–24%, and NNTs of 1.9 or 2.0. Reporting of withdrawals was less consistent, but all-cause withdrawals for sildenafil, tadalafil and vardenafil were 8% 13% and 20%. All three drugs were well tolerated, with headache being the most commonly reported event at 13–17%. There were few serious adverse events.

Conclusion

There were differences between trials in outcomes reported, limiting comparisons, and the most useful outcomes were not reported. For common outcomes there was similar efficacy between PDE-5 inhibitors.
Technical efficiency of peripheral health units in Pujehun district of Sierra Leone: a DEA application
Authors: Renner Ade , Kirigia Joses M , Zere Eyob A , Barry Saidou P , Kirigia Doris G , Kamara Clifford , Muthuri Lenity HK
Published: December 2005

Background

The Data Envelopment Analysis (DEA) method has been fruitfully used in many countries in Asia, Europe and North America to shed light on the efficiency of health facilities and programmes. There is, however, a dearth of such studies in countries in sub-Saharan Africa. Since hospitals and health centres are important instruments in the efforts to scale up pro-poor cost-effective interventions aimed at achieving the United Nations Millennium Development Goals, decision-makers need to ensure that these health facilities provide efficient services. The objective of this study was to measure the technical efficiency (TE) and scale efficiency (SE) of a sample of public peripheral health units (PHUs) in Sierra Leone.

Methods

This study applied the Data Envelopment Analysis approach to investigate the TE and SE among a sample of 37 PHUs in Sierra Leone.

Results

Twenty-two (59%) of the 37 health units analysed were found to be technically inefficient, with an average score of 63% (standard deviation = 18%). On the other hand, 24 (65%) health units were found to be scale inefficient, with an average scale efficiency score of 72% (standard deviation = 17%).

Conclusion

It is concluded that with the existing high levels of pure technical and scale inefficiency, scaling up of interventions to achieve both global and regional targets such as the MDG and Abuja health targets becomes far-fetched. In a country with per capita expenditure on health of about US$7, and with only 30% of its population having access to health services, it is demonstrated that efficiency savings can significantly augment the government's initiatives to cater for the unmet health care needs of the population. Therefore, we strongly recommend that Sierra Leone and all other countries in the Region should institutionalise health facility efficiency monitoring at the Ministry of Health headquarter (MoH/HQ) and at each health district headquarter.
The economic value of an improved malaria treatment programme in Zambia: results from a contingent valuation survey
Authors: Masiye Felix , Rehnberg Clas
Published: December 2005

Background

Zambia is facing a double crisis of increasing malaria burden and dwindling capacity to deal with the endemic malaria burden. The pursuit of sustainable but equity mechanisms for financing malaria programmes is a subject of crucial policy discussion. This requires that comprehensive accounting of the economic impact of the various malaria programmes. Information on the economic value of programmes is essential in soliciting appropriate funding allocations for malaria control.

Aims and objectives

This paper specifically seeks to elicit a measure of the economic benefits of an improved malaria treatment programme in Zambia. The paper also studies the equity implications in malaria treatment given that demand or malaria treatment is determined by household socio-economic status.

Methods

A contingent valuation survey of about 300 Zambian households was conducted in four districts. Willingness-to-pay (WTP) was elicited for an improved treatment programme for malaria in order to generate a measure of the economic benefits of the programme. The payment card method was used in eliciting WTP bids.

Findings

The study reports that malaria treatment has significant economic benefits to society. The total economic benefits of an improved treatment programme were estimated at an equivalent of US$ 77 million per annum, representing about 1.8% of Zambia's GDP. The study also reports the theoretically anticipated association between WTP and several socio-economic factors. Our income elasticity of demand is positive and similar in magnitude to estimates reported in similar studies. Finally, from an equity standpoint, the constraints imposed by income and socio-economic status are discussed.
Rapid screening for glucose-6-phosphate dehydrogenase deficiency and haemoglobin polymorphisms in Africa by a simple high-throughput SSOP-ELISA method
Authors: Enevold Anders , Vestergaard Lasse S , Lusingu John , Drakeley Chris J , Lemnge Martha M , Theander Thor G , Bygbjerg Ib C , Alifrangis Michael
Published: December 2005

Background

Mutations in the haemoglobin beta-globin (HbB) and glucose-6-phosphate dehydrogenase (G6PD) genes cause widespread human genetic disorders such as sickle cell diseases and G6PD deficiency. In sub-Saharan Africa, a few predominant polymorphic variants of each gene account for a majority of these deficiencies. Examining at a larger scale the clinical importance of these independent genetic disorders, their possible association with malaria pathogenesis and innate resistance, and their relevance for antimalarial drug treatment, would be easier if an accurate screening method with limited costs was available.

Methods

A simple and rapid technique was developed to detect the most prominent single nucleotide polymorphisms (SNPs) in the HbB and G6PD genes. The method is able to detect the different haemoglobin polymorphisms A, S, C and E, as well as G6PD polymorphisms B, A and A- based on PCR-amplification followed by a hybridization step using sequence-specific oligonucleotide probes (SSOPs) specific for the SNP variants and quantified by ELISA.

Results

The SSOP-ELISA method was found to be specific, and compared well to the commonly used PCR-RFLP technique. Identical results were obtained in 98% (haemoglobin) and 95% (G6PD) of the tested 90 field samples from a high-transmission area in Tanzania, which were used to validate the new technique.

Conclusion

The simplicity and accuracy of the new methodology makes it suitable for application in settings where resources are limited. It would serve as a valuable tool for research purposes by monitoring genotype frequencies in relation to disease epidemiology.
Exclusion of PINK1 as candidate gene for the late-onset form of Parkinson's disease in two European populations
Authors: Schlitter Anna Melissa , Kurz Martin , Larsen Jan P , Woitalla Dirk , Mueller Thomas , Epplen Joerg T , Dekomien Gabriele
Published: December 2005

Background

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Recently, mutations in the PINK1 (PARK6) gene were shown to rarely cause autosomal-recessively transmitted, early-onset parkinsonism. In order to evaluate whether PINK1 contributes to the risk of common late-onset PD we analysed PINK1 sequence variations. A German (85 patients) and a Norwegian cohort (90 patients) suffering from late-onset PD were screened for mutations and single nucleotide polymorphisms (SNPs) in the PINK1 gene. Both cohorts consist of well-characterized patients presenting a positive family history of PD in ~17%. Investigations were performed by single strand conformation polymorphism (SSCP), denaturating high performance liquid chromatography (DHPLC) and sequencing analyses. SNP frequencies were compared by the χ2 test

Results

Several common SNPs were identified in our cohorts, including a recently identified coding variant (Q115L) in exon 1. Genotyping of the Q115L variation did not reveal significant frequency differences between patients and controls. Pathogenic mutations in the PINK1 gene were not identified, neither in the German nor in the Norwegian cohort.

Conclusion

Sequence variation in the PINK1 gene appears to play a marginal quantitative role in the pathogenesis of the late-onset form of PD, in German and Norwegian cohorts, if at all.
Clinical benefit of metaphase I oocytes
Authors: Vanhoutte Leen , De Sutter Petra , Van der Elst Josiane , Dhont Marc
Published: December 2005

Background

We studied the benefit of using in vitro matured metaphase I (MI) oocytes for ICSI in patients with a maximum of 6 mature metaphase II (MII) oocytes at retrieval.

Methods

In 2004, 187 ICSI cycles were selected in which maximum 6 MII oocytes and at least one MI oocyte were retrieved. MI oocytes were put in culture to mature until the moment of ICSI, which was performed between 2 to 11 hours after oocyte retrieval (day 0). In exceptional cases, when the patient did not have any mature oocyte at the scheduled time of ICSI, MI oocytes were left to mature overnight and were injected between 19 to 26 hours after retrieval (day 1). Embryos from MI oocytes were chosen for transfer only when no other good quality embryos from MII oocytes were available. Outcome parameters were time period of in vitro maturation (IVM), IVM and fertilization rates, embryo development, clinical pregnancy rates, implantation rates and total MI oocyte utilization rate.

Results

The overall IVM rate was 43%. IVM oocytes had lower fertilization rates compared to in vivo matured sibling oocytes (52% versus 68%, P < 0.05). The proportion of poor quality embryos was significantly higher in IVM derived oocytes. One pregnancy and live birth was obtained out of 13 transfers of embryos exclusively derived from IVM oocytes. This baby originated from an oocyte that was injected after 22 hrs of IVM.

Conclusion

Fertilization of in vitro matured MI oocytes can result in normal embryos and pregnancy, making IVM worthwhile, particularly when few MII oocytes are obtained at retrieval.
Implementation failures in the use of two New Zealand laws to control the tobacco industry: 1989–2005
Authors: Thomson George , Wilson Nick
Published: December 2005

Background

We reviewed the implementation of New Zealand laws in relation to the activities of the tobacco industry and their allies. Material for two brief case studies was obtained from correspondence with official agencies, official information requests, internet searches (tobacco industry documents and official government sites), and interviews with 12 key informants.

Results

The first case study identified four occasions over a period of 14 years where New Zealand Government agencies appeared to fail to enforce consumer protection law, although apparent breaches by the tobacco industry and their allies had occurred in relation to statements on the relative safety of secondhand smoke. The second case study examined responses to a legal requirement for the tobacco industry to provide information on tobacco additives. There was failure to enforce the law, and a failure of the political process for at least 13 years to clarify and strengthen the law. Relevant factors in both these cases of 'policy slippage' appear to have been financial and opportunity costs of taking legal action, political difficulties and the fragmented nature of government structures.

Conclusion

Considered together, these case studies suggest the need for governments to: (i) make better use of national consumer laws (with proper monitoring and enforcement) in relation to tobacco; and (ii) to strengthen international law and resources around tobacco-related consumer protection. A number of options for achieving these aims are available to governments.
Policy lessons from comparing mortality from two global forces: international terrorism and tobacco
Authors: Thomson George , Wilson Nick
Published: December 2005

Background

The aim of this study was to compare the mortality burdens from two global impacts on mortality: international terrorism and the major cause of preventable death in developed countries – tobacco use. We also sought to examine the similarities and differences between these two causes of mortality so as to better inform the policy responses directed at prevention.

Methods

Data on deaths from international terrorism were obtained from a US State Department database for 1994–2003. Estimates for tobacco-attributable deaths were based on Peto et al 2003. The countries were 37 developed and East European countries.

Results and discussion

The collective annualized mortality burden from tobacco was approximately 5700 times that of international terrorism. The ratio of annual tobacco to international terrorism deaths was lowest for the United States at 1700 times, followed by Russia at 12,900 times. The tobacco death burden in all these countries was equivalent to the impact of an 11 September type terrorist attack every 14 hours.

Different perceptions of risk may contribute to the relative lack of a policy response to tobacco mortality, despite its relatively greater scale. The lack is also despite tobacco control having a stronger evidence base for the prevention measures used.

Conclusion

This comparison highlights the way risk perception may determine different policy responses to global forces causing mortality. Nevertheless, the large mortality differential between international terrorism and tobacco use has policy implications for informing the rational use of resources to prevent premature death.
Compound developmental eye disorders following inactivation of TGFβ signaling in neural-crest stem cells
Authors: Ittner Lars M , Wurdak Heiko , Schwerdtfeger Kerstin , Kunz Thomas , Ille Fabian , Leveen Per , Hjalt Tord A , Suter Ueli , Karlsson Stefan , Hafezi Farhad , Born Walter , Sommer Lukas
Published: December 2005

Background

Development of the eye depends partly on the periocular mesenchyme derived from the neural crest (NC), but the fate of NC cells in mammalian eye development and the signals coordinating the formation of ocular structures are poorly understood.

Results

Here we reveal distinct NC contributions to both anterior and posterior mesenchymal eye structures and show that TGFβ signaling in these cells is crucial for normal eye development. In the anterior eye, TGFβ2 released from the lens is required for the expression of transcription factors Pitx2 and Foxc1 in the NC-derived cornea and in the chamber-angle structures of the eye that control intraocular pressure. TGFβ enhances Foxc1 and induces Pitx2 expression in cell cultures. As in patients carrying mutations in PITX2 and FOXC1, TGFβ signal inactivation in NC cells leads to ocular defects characteristic of the human disorder Axenfeld-Rieger's anomaly. In the posterior eye, NC cell-specific inactivation of TGFβ signaling results in a condition reminiscent of the human disorder persistent hyperplastic primary vitreous. As a secondary effect, retinal patterning is also disturbed in mutant mice.

Conclusion

In the developing eye the lens acts as a TGFβ signaling center that controls the development of eye structures derived from the NC. Defective TGFβ signal transduction interferes with NC-cell differentiation and survival anterior to the lens and with normal tissue morphogenesis and patterning posterior to the lens. The similarity to developmental eye disorders in humans suggests that defective TGFβ signal modulation in ocular NC derivatives contributes to the pathophysiology of these diseases.
On a localization property of wavelet coefficients for processes with stationary increments, and applications. I. Localization with respect to shift
Authors: Albeverio Sergio , Kawasaki Shuji
Published: December 2005

We formulate a localization property of wavelet coefficients for processes with stationary increments, in the estimation problem associated with the processes. A general setting for the estimation is adopted and examples that fit this setting are given. An evaluation of wavelet coefficient decay with respect to shiftk∈ℕ is explicitly derived (only the asymptotic behavior, for largek, was previously known). It is this evaluation that makes it possible to establish the localization property of the wavelet coefficients. In doing so, it turns out that the theory of positive-definite functions plays an important role. As applications, we show that, in the wavelet coefficient domain, estimators that use a simple moment method are nearly as good as maximum likelihood estimators. Moreover, even though the underlying process is long-range dependent and process domain estimates imply the validity of a noncentral limit theorem, for the wavelet coefficient domain estimates we always obtain a central limit theorem with a small prescribed error.
Extremes of regularly varying Lévy-driven mixed moving average processes
Authors: Fasen Vicky
Published: December 2005

In this paper, we study the extremal behavior of stationary mixed moving average processes of the form
Y(t)=∫ℝ+×ℝf(r,t-s) dΛ(r,s), t∈ℝ, where f is a deterministic function and Λ is an infinitely divisible, independently scattered random measure whose underlying driving Lévy process is regularly varying. We give sufficient conditions for the stationarity of Y and compute the tail behavior of certain functionals of Y. The extremal behavior is modeled by marked point processes on a discrete-time skeleton chosen properly by the jump times of the underlying driving Lévy process and the extremes of the kernel function. The sequences of marked point processes converge weakly to a cluster Poisson random measure and reflect extremes of Y at a high level. We also show convergence of the partial maxima to the Fréchet distribution. Our models and results cover short- and long-range dependence regimes.
Conditioning an additive functional of a Markov chain to stay nonnegative. I. Survival for a long time
Authors: Jacka Saul D. , Lazic Zorana , Warren Jon
Published: December 2005

Let (Xt)t≥0 be a continuous-time irreducible Markov chain on a finite state space E, let v be a map v: E→ℝ\{0}, and let (φt)t≥0 be an additive functional defined by φt=∫0tv(Xs)d s. We consider the case in which the process (φt)t≥0 is oscillating and that in which (φt)t≥0 has a negative drift. In each of these cases, we condition the process (Xt,φt)t≥0 on the event that (φt)t≥0 is nonnegative until time T and prove weak convergence of the conditioned process as T→∞.
Conditioning an additive functional of a Markov chain to stay nonnegative. II. Hitting a high level
Authors: Jacka Saul D. , Lazic Zorana , Warren Jon
Published: December 2005

Let (Xt)t≥0 be a continuous-time irreducible Markov chain on a finite state space E, let v: E→ℝ\{0}, and let (φt)t≥0 be defined by φt=∫0tv(Xs)d s. We consider the case in which the process (φt)t≥0 is oscillating and that in which (φt)t≥0 has a negative drift. In each of these cases, we condition the process (Xt,φt)t≥0 on the event that (φt)t≥0 hits level y before hitting 0 and prove weak convergence of the conditioned process as y→∞. In addition, we show the relationship between the conditioning of the process (φt)t≥0 with a negative drift to oscillate and the conditioning of it to stay nonnegative for a long time, and the relationship between the conditioning of (φt)t≥0 with a negative drift to drift to ∞ and the conditioning of it to hit large levels before hitting 0.
Power spectra of random spike fields and related processes
Authors: Brémaud Pierre , Massoulié Laurent , Ridolfi Andrea
Published: December 2005

In this article, we review known results and present new ones concerning the power spectra of large classes of signals and random fields driven by an underlying point process, such as spatial shot noises (with random impulse response and arbitrary basic stationary point processes described by their Bartlett spectra) and signals or fields sampled at random times or points (where the sampling point process is again quite general). We also obtain the Bartlett spectrum for the general linear Hawkes spatial branching point process (with random fertility rate and general immigrant process described by its Bartlett spectrum). We then obtain the Bochner spectra of general spatial linear birth and death processes. Finally, we address the issues of random sampling and linear reconstruction of a signal from its random samples, reviewing and extending former results.
Nonstationary value iteration in controlled Markov chains with risk-sensitive average criterion
Authors: Cavazos-Cadena Rolando , Montes-De-Oca Raúl
Published: December 2005

This work concerns Markov decision chains with finite state spaces and compact action sets. The performance index is the long-run risk-sensitive average cost criterion, and it is assumed that, under each stationary policy, the state space is a communicating class and that the cost function and the transition law depend continuously on the action. These latter data are not directly available to the decision-maker, but convergent approximations are known or are more easily computed. In this context, the nonstationary value iteration algorithm is used to approximate the solution of the optimality equation, and to obtain a nearly optimal stationary policy.
A new urn model
Authors: Chen May-Ru , Wei Ching-Zong
Published: December 2005

In this paper, we propose a new urn model. A single urn contains b black balls and w white balls. For each observation, we randomly draw m balls and note their colors, say k black balls and m − k white balls. We return the drawn balls to the urn with an additional ck black balls and c(m − k) white balls. We repeat this procedure n times and denote by Xn the fraction of black balls after the nth draw. To investigate the asymptotic properties of Xn, we first perform some computational studies. We then show that {Xn} forms a martingale, which converges almost surely to a random variable X. The distribution of X is then shown to be absolutely continuous.
Waiting time distributions of competing patterns in higher-order Markovian sequences
Authors: Aston John A. D. , Martin Donald E. K.
Published: December 2005

Competing patterns are compound patterns that compete to be the first to occur pattern-specific numbers of times. They represent a generalisation of the sooner waiting time problem and of start-up demonstration tests with both acceptance and rejection criteria. Through the use of finite Markov chain imbedding, the waiting time distribution of competing patterns in multistate trials that are Markovian of a general order is derived. Also obtained are probabilities that each particular competing pattern will be the first to occur its respective prescribed number of times, both in finite time and in the limit.
Level-crossing ordering of semi-Markov processes and markov chains
Authors: Ferreira Fátima , Pacheco António
Published: December 2005

We extend the definition of level-crossing ordering of stochastic processes, proposed by Irle and Gani (2001), to the case in which the times to exceed levels are compared using an arbitrary stochastic order, and work, in particular, with integral stochastic orders closed for convolution. Using a sample-path approach, we establish level-crossing ordering results for the case in which the slower of the processes involved in the comparison is skip-free to the right. These results are specially useful in simulating processes that are ordered in level crossing, and extend results of Irle and Gani (2001), Irle (2003), and Ferreira and Pacheco (2005) for skip-free-to-the-right discrete-time Markov chains, semi-Markov processes, and continuous-time Markov chains, respectively.
Sensitivity and convergence of uniformly ergodic Markov chains
Authors: Mitrophanov A. Yu.
Published: December 2005

For uniformly ergodic Markov chains, we obtain new perturbation bounds which relate the sensitivity of the chain under perturbation to its rate of convergence to stationarity. In particular, we derive sensitivity bounds in terms of the ergodicity coefficient of the iterated transition kernel, which improve upon the bounds obtained by other authors. We discuss convergence bounds that hold in the case of finite state space, and consider numerical examples to compare the accuracy of different perturbation bounds.
On the geometric growth in a class of homogeneous multitype Markov chain
Authors: González M. , Martínez R. , Mota M.
Published: December 2005

In this paper, we investigate the geometric growth of homogeneous multitype Markov chains whose states have nonnegative integer coordinates. Such models are considered in a situation similar to the supercritical case for branching processes. Finally, our general theoretical results are applied to a class of controlled multitype branching process in which the control is random.
Simple derivations of properties of counting processes associated with Markov renewal processes
Authors: Ball Frank , Milne Robin K.
Published: December 2005

A simple, widely applicable method is described for determining factorial moments of N̂t, the number of occurrences in (0,t] of some event defined in terms of an underlying Markov renewal process, and asymptotic expressions for these moments as t → ∞. The factorial moment formulae combine to yield an expression for the probability generating function of N̂t, and thereby further properties of such counts. The method is developed by considering counting processes associated with events that are determined by the states at two successive renewals of a Markov renewal process, for which it both simplifies and generalises existing results. More explicit results are given in the case of an underlying continuous-time Markov chain. The method is used to provide novel, probabilistically illuminating solutions to some problems arising in the stochastic modelling of ion channels.
Large-time asymptotics for the density of a branching Wiener process
Authors: Révész Pál , Rosen Jay , Shi Zhan
Published: December 2005

Given an ℝd-valued supercritical branching Wiener process, let ψ(A, T) be the number of particles in A ⊂ ℝd at time T (T = 0, 1, 2, …). We provide a complete asymptotic expansion of ψ(A, T) as T → ∞, generalizing the work of X. Chen.
Alternating branching processes
Authors: Mayster Penka
Published: December 2005

We introduce the idea of controlling branching processes by means of another branching process, using the fractional thinning operator of Steutel and van Harn. This idea is then adapted to the model of alternating branching, where two Markov branching processes act alternately at random observation and treatment times. We study the extinction probability and limit theorems for reproduction by n cycles, as n → ∞.
A multitype contact process with frozen sites: a spatial model of allelopathy
Authors: Lanchier Nicolas
Published: December 2005

In this paper, we introduce a generalization of the two-color multitype contact process intended to mimic a biological process called allelopathy. To be precise, we have two types of particle. Particles of each type give birth to particles of the same type, and die at rate 1. When a particle of type 1 dies, it gives way to a frozen site that blocks particles of type 2 for an exponentially distributed amount of time. Specifically, we investigate in detail the phase transitions and the duality properties of the interacting particle system.
A large deviation principle for a Brownian immigration particle system
Authors: Zhang Mei
Published: December 2005

We derive a large deviation principle for a Brownian immigration branching particle system, where the immigration is governed by a Poisson random measure with a Lebesgue intensity measure.
A renewal-process-type expression for the moments of inverse subordinators
Authors: Lagerås Andreas Nordvall
Published: December 2005

We define an inverse subordinator as the passage times of a subordinator to increasing levels. It has previously been noted that such processes have many similarities to renewal processes. Here we present an expression for the joint moments of the increments of an inverse subordinator. This is an analogue of a result for renewal processes. The main tool is a theorem on processes which are both renewal processes and Cox processes.
A planar random motion with an infinite number of directions controlled by the damped wave equation
Authors: Kolesnik Alexander D. , Orsingher Enzo
Published: December 2005

We consider the planar random motion of a particle that moves with constant finite speed c and, at Poisson-distributed times, changes its direction θ with uniform law in [0, 2π). This model represents the natural two-dimensional counterpart of the well-known Goldstein–Kac telegraph process. For the particle's position (X(t), Y(t)), t > 0, we obtain the explicit conditional distribution when the number of changes of direction is fixed. From this, we derive the explicit probability law f(x, y, t) of (X(t), Y(t)) and show that the density p(x, y, t) of its absolutely continuous component is the fundamental solution to the planar wave equation with damping. We also show that, under the usual Kac condition on the velocity c and the intensity λ of the Poisson process, the density p tends to the transition density of planar Brownian motion. Some discussions concerning the probabilistic structure of wave diffusion with damping are presented and some applications of the model are sketched.
Optimality of the 2-CUSUM drift equalizer rules for detecting two-sided alternatives in the Brownian motion model
Authors: Hadjiliadis Olympia
Published: December 2005

This work employs the Brownian motion model in which observations are taken sequentially. The objective is to detect a two-sided change in the constant drift by means of a stopping rule. As a performance measure, an extended Lorden criterion is used. The goal is to minimize the worst-case detection delay subject to a constraint in the frequency of false alarms. In a companion paper, attention is drawn to a first category of 2-CUSUM rules for which the harmonic mean rule holds. It is further seen that a special class of 2-CUSUM stopping rules within this category, called drift equalizer rules, perform strictly better than non-equalizer rules, according to this specific performance measure.
The closure of a local subexponential distribution class under convolution roots, with applications to the compound Poisson process
Authors: Wang Yuebao , Cheng Dongya , Wang Kaiyong
Published: December 2005

Let denote the class of local subexponential distributions and F∗ν the ν-fold convolution of distribution F, where ν belongs to one of the following three cases: ν is a random variable taking only a finite number of values, in particular ν ≡ n for some n ≥ 2; ν is a Poisson random variable; or ν is a geometric random variable. Along the lines of Embrechts, Goldie, and Veraverbeke (1979), the following assertion is proved under certain conditions: This result is applied to the infinitely divisible laws and some new results are established. The results obtained extend the corresponding findings of Asmussen, Foss, and Korshunov (2003).
Chromosomal clustering and GATA transcriptional regulation of intestine-expressed genes inC. elegans
Authors: Pauli Florencia , Liu Yueyi , Kim Yoona A. , Chen Pei-Jiun , Kim Stuart K.
Published: December 2005

We used mRNA tagging to identify genes expressed in the intestine of C. elegans. Animals expressing an epitope-tagged protein that binds the poly-A tail of mRNAs (FLAG::PAB-1) from an intestine-specific promoter(ges-1) were used to immunoprecipitate FLAG::PAB-1/mRNA complexes from the intestine. A total of 1938 intestine-expressed genes(P<0.001) were identified using DNA microarrays. First, we compared the intestine-expressed genes with those expressed in the muscle and germline, and identified 510 genes enriched in all three tissues and 624 intestine-, 230 muscle- and 1135 germ line-enriched genes. Second, we showed that the 1938 intestine-expressed genes were physically clustered on the chromosomes, suggesting that the order of genes in the genome is influenced by the effect of chromatin domains on gene expression. Furthermore, the commonly expressed genes showed more chromosomal clustering than the tissue-enriched genes, suggesting that chromatin domains may influence housekeeping genes more than tissue-specific genes. Third, in order to gain further insight into the regulation of intestinal gene expression, we searched for regulatory motifs. This analysis found that the promoters of the intestine genes were enriched for the GATA transcription factor consensus binding sequence. We experimentally verified these results by showing that the GATA motif is required in cis and that GATA transcription factors are required in trans for expression of these intestinal genes.
Use of time-lapse imaging and dominant negative receptors to dissect the steroid receptor control of neuronal remodeling inDrosophila
Authors: Brown Heather L. D. , Cherbas Lucy , Cherbas Peter , Truman James W.
Published: December 2005

During metamorphosis, the reorganization of the nervous system of Drosophila melanogaster proceeds in part through remodeling of larval neurons. In this study, we used in-vitro imaging techniques and immunocytochemistry to track the remodeling of the thoracic ventral neurosecretory cells. Axons of these neurons prune their larval arbors early in metamorphosis and a larger, more extensive adult arbor is established via branch outgrowth. Expression of EcR dominant negative constructs and an EcR inverted repeat construct resulted in pruning defects of larval axon arbors and a lack of filopodia during pruning, but showed variable effects on outgrowth depending on the construct expressed. Cells expressing either UAS-EcR-B1W650A or UAS-EcR-AW650A lacked filopodia during the outgrowth period and formed a poorly branched, larval-like arbor in the adult. Cells expressing UAS-EcR-B1F645A,UAS-EcR-B2W650A or UAS-IR-EcR (core) showed moderate filopodial activity and normal, albeit reduced, adult-like branching during outgrowth. These results are consistent with the role of activation versus derepression via EcR for successive phases of neuronal remodeling and suggest that functional ecdysone receptor is necessary for some, but not all, remodeling events.
Convergence of Wnt and FGF signals in the genesis of posterior neural plate through activation of theSox2enhancer N-1
Authors: Takemoto Tatsuya , Uchikawa Masanori , Kamachi Yusuke , Kondoh Hisato
Published: December 2005

The expression of the transcription factor gene Sox2 precisely marks the neural plate in various vertebrate species. We previously showed that the Sox2 expression prevailing in the neural plate of chicken embryos is actually regulated by the coordination of five phylogenetically conserved enhancers having discrete regional coverage, among which the 420-bp long enhancer N-1, active in the node-proximal region, is probably involved directly in the genesis of the posterior neural plate. We investigated the signaling systems regulating this enhancer, first identifying the 56-bp N-1 core enhancer (N-1c), which in a trimeric form recapitulates the activity of the enhancer N-1. Mutational analysis identified five blocks, A to E, that regulate the enhancer N-1c. Functional analysis of these blocks indicated that Wnt and FGF signals synergistically activate the enhancer through Blocks A-B,bound by Lef1, and Block D, respectively. Fgf8b and Wnt8cexpressed in the organizer-primitive streak region account for the activity in the embryo. Block E is essential for the repression of the enhancer N-1c activity in the mesendodermal precursors. The enhancer N-1c is not affected by BMP signals. Thus, Wnt and FGF signals converge to activate Sox2expression through the enhancer N-1c, revealing the direct involvement of the Wnt signal in the initiation of neural plate development.
Cognition and Hierarchy: Rethinking the Microfoundations of Capabilities’ Development
Authors: Gavetti Giovanni
Published: December 2005

This article identifies gaps in the microfoundations of capabilities research, particularly in work that is based on the framework of evolutionary economics. It argues that such research has focused excessively on the quasi-automatic, routine-based aspects of capability development, and largely neglected the roles played by cognition and organizational hierarchy. By deriving a model of search that jointly considers how routine-based and cognitive logics of action coexist within an organizational hierarchy to affect capability development, this article offers three contributions. First, it delineates the traits of a microfoundational structure for research on capabilities that begins to address these gaps. Second, based on this structure, it highlights previously neglected causal mechanisms that contribute to our understanding of how capabilities develop. The model shows that managers’ cognitive representations of their strategic decision problem fundamentally drive organizational search, and therefore the accumulation of capabilities. Furthermore, it shows that the accuracy of the representations a manager chooses might vary according to where she is situated in the organizational hierarchy. This more refined perspective leads to a set of propositions regarding how different hierarchical arrangements influence capability development and organizational performance. Finally, the paper sets an agenda for future research in this area.
When the Market Misleads: Stock Prices, Firm Behavior, and Industry Evolution
Authors: Kock Carl Joachim
Published: December 2005

This paper augments learning and institutional theories of firm behavior with an explicit focus on the idiosyncratic characteristics of learning from financial markets. Various streams of literature implicitly assume that financial markets influence firm strategies, yet the specifics of these interactions are not well specified. Motivated by a case study of the retail brokerage industry, this study proposes three particular characteristics of learning from financial markets. First, there is vicarious learning from outcomes (e.g., stock valuations), yet this has characteristics that are more similar to institutional forms of mimetic isomorphism. Second, the forward-looking and complex nature of financial valuations incites a paradoxically simplified type of crude heuristic learning. Third, there is a mutual and simultaneous learning process in that firms learn from financial markets, which in turn are themselves in a process of social construction. This combination of special characteristics suggests a number of learning pathologies that center around an increasing likelihood (compared with other types of learning and adaptation) of falling prey to misleading signals. A computer simulation, based on a model in which Cournot duopolists play a multistage game involving investment and cost reduction, explores the implications of these characteristics and pathologies in a systematic way.
Intrafirm Competition and Charter Evolution in the Multibusiness Firm
Authors: Birkinshaw Julian , Lingblad Mats
Published: December 2005

We develop a theoretical framework for a specific form of intrafirm competition, namely the extent of overlap between the charters of two or more units in a single organization. This phenomenon is commonly seen in large organizations, e.g., cases of two business units producing competing products, or two product development groups trying to solve the same technological problem, but the existing academic literature provides little insight into the forms intrafirm competition takes, or the conditions under which it is beneficial or harmful to the organization.

Building on the concept of an organization charter (Galunic and Eisenhardt 2001), we identify two generic forms of intrafirm competition: the dynamic community model has fluid and frequently changing charter boundaries, and it emerges through the creation of strategic options in the face of a changing environment; the coexistence model has fixed and relatively static charter boundaries, and it owes its existence to economies of scope and differentiation of unit charters to cover multiple market segments. In the body of the paper we develop a theoretical framework to specify the environmental and organizational conditions under which each form of intrafirm competition is expected to occur.
Preadaptation, Firm Heterogeneity, and Technological Performance: A Study on the Evolution of Fiber Optics, 1970–1995
Authors: Cattani Gino
Published: December 2005

Strategy research typically traces stable performance differences among firms to a priori heterogeneity in initial resource endowments or in expected flows of resources. The objective of this paper is to explore how this heterogeneity is created and how it affects firm technological performance. Within the framework of an evolutionary view of technological change, we develop the notion of technological preadaptation to describe that part of a firm’s prior experience that is accumulated without anticipation of subsequent uses. In particular, we hypothesize that (technological) performance differences are positively related to (1) firms’ stock of relevant skills and knowledge potentially available for applications other than those for which they were originally developed and (2) the extent to which firms actually build on these skills and knowledge in new domains. The empirical setting is fiber optics technology as it evolved for use in long-distance communications between 1970 and 1995. We find that “preadapted” firms that consistently leveraged their prior experience achieved higher levels of performance than did firms that did not leverage that experience or did not have prior experience. The study illustrates the importance of preadaptation in capability development and technological competition.
As the Twig Is Bent: How Group Values Shape Emergent Task Interdependence in Groups
Authors: Wageman Ruth , Gordon Frederick M.
Published: December 2005

This paper proposes that task interdependence in teams, usually treated solely as structurally driven, can arise from group members’ values at the time of group formation. Findings from a longitudinal field study show that teams whose members share egalitarian values at formation develop highly interdependent task approaches and exhibit patterns of social interaction similar to those associated with high structural interdependence. By contrast, groups whose members share meritocratic values at formation develop low-interdependence task approaches and exhibit patterns of social interaction similar to those associated with low structural interdependence. Groups with shared hybrid or with mixed values show no consistent task structures or group processes, and significantly underperform relative to both the egalitarian and the meritocratic groups. We discuss the implications of these findings for the effectiveness of task-performing teams in organizations.
The Persistence of Flexible Organizational Routines: The Role of Agency and Organizational Context
Authors: Howard-Grenville Jennifer A.
Published: December 2005

Once regarded as stable and inflexible, organizational routines are increasingly seen as capable of being adapted to the situation at hand and a potentially important source of endogenous change in organizations. This paper considers why routines that are performed flexibly may nonetheless persist over time. Drawing on data from participant observation of a high-tech manufacturing company, I identify factors that contribute to both the flexibility and persistence of a routine. First, individuals and groups approach routines with different intentions and orientations, suggesting that agency shapes particular routine performances. Second, routine performances are embedded in an organizational context that, while it may not restrict the flexible use of a routine, may constrain its ongoing adaptation. Finally, accounting for the relative power of individuals sheds light on the interaction between agency and context in routine performance and explains why the actions of some individuals, but not others, can change routines. This paper draws on recent work that conceptualizes routines as ongoing accomplishments, and it extends it by identifying how actors and contexts shape both individual performances of routines and contribute to their persistence or change over time.
Reputation, Diversification, and Organizational Explanations of Performance in Professional Service Firms
Authors: Greenwood Royston , Li Stan X. , Prakash Rajshree , Deephouse David L.
Published: December 2005

Growing interest in knowledge as a competitive asset suggests the benefit of studying professional service firms (PSFs). These firms are highly successful examples of organizations whose ability to manage knowledge is critical to their success. Furthermore, they are worthy of study because they constitute a significant sector of the economy, whether measured by their size, numbers, or influence. Despite their significance, little is known of the determinants of their performance. This paper proposes that the core tasks of PSFs raise unusual strategic and organizational challenges, the resolution of which affects organizational performance. We elaborate the effects of reputation and diversification and contrast them to theory for goods-producing industries. We also hypothesize that PSF managers face a choice in designing structures between the retention and motivation of the professional workforce and transferring knowledge from partners to other professionals. These predictions are tested and supported by data from the largest 100 U.S. accounting firms for the period 1991–2000. The paper thus contributes to a theory of professional service firm management.
The influence of thein situstate of sands on the load–deflection behaviour of driven piles
Authors: Coop M. R. , Klotz E. U. , Clinton L.
Published: December 2005

A series of pile load tests was carried out in a centrifuge model, investigating the influence of the in situ volume–stress state on the load–deflection behaviour. Two sands of different mineralogies were tested at a variety of accelerations and sample densities. In each case a good correlation was found between the load–deflection behaviour and the in situ state quantified by the distance of the initial state from the critical state line in the v–ln p′ plane. How the soil arrived at its initial state, whether by compaction or overconsolidation, did not have a significant impact on the load–deflection behaviour. Repeated loading with a zero head load condition maintained between each cycle was not found to influence significantly the capacity or stiffness of response, but loading the pile to its full tensile capacity was found to reduce significantly the stiffness of response in compression.