bluuebunny/crossref_metadata_2025 huggingface dataset:
Human Cytomegalovirus Infection Causes Premature and Abnormal Differentiation of Human Neural Progenitor Cells
Authors: Luo Min Hua , Hannemann Holger , Kulkarni Amit S. , Schwartz Philip H. , O'Dowd John M. , Fortunato Elizabeth A.
Published: January 2010

Congenital human cytomegalovirus (HCMV) infection is a leading cause of birth defects, largely manifested as central nervous system (CNS) disorders. The principal site of manifestations in the mouse model is the fetal brain's neural progenitor cell (NPC)-rich subventricular zone. Our previous human NPC studies found these cells to be fully permissive for HCMV and a usefulin vitromodel system. In continuing work, we observed that under culture conditions favoring maintenance of multipotency, infection caused NPCs to quickly and abnormally differentiate. This phenotypic change required active viral transcription. Whole-genome expression analysis found rapid downregulation of genes that maintain multipotency and establish NPCs’ neural identity. Quantitative PCR, Western blot, and immunofluorescence assays confirmed that the mRNA and protein levels of four hallmark NPC proteins (nestin, doublecortin, sex-determining homeobox 2, and glial fibrillary acidic protein) were decreased by HCMV infection. The decreases required active viral replication and were due, at least in part, to proteasomal degradation. Our results suggest that HCMV infection causesin uteroCNS defects by inducing both premature and abnormal differentiation of NPCs.
Assessment of Seasonal Influenza A Virus-Specific CD4 T-Cell Responses to 2009 Pandemic H1N1 Swine-Origin Influenza A Virus
Authors: Ge Xinhui , Tan Venus , Bollyky Paul L. , Standifer Nathan E. , James Eddie A. , Kwok William W.
Published: January 2010

Very limited evidence has been reported to show human adaptive immune responses to the 2009 pandemic H1N1 swine-origin influenza A virus (S-OIV). We studied 17 S-OIV peptides homologous to immunodominant CD4 T epitopes from hemagglutinin (HA), neuraminidase (NA), nuclear protein (NP), M1 matrix protein (MP), and PB1 of a seasonal H1N1 strain. We concluded that 15 of these 17 S-OIV peptides would induce responses of seasonal influenza virus-specific T cells. Of these, seven S-OIV sequences were identical to seasonal influenza virus sequences, while eight had at least one amino acid that was not conserved. T cells recognizing epitopes derived from these S-OIV antigens could be detected
ex vivo
. Most of these T cells expressed memory markers, although none of the donors had been exposed to S-OIV. Functional analysis revealed that specific amino acid differences in the sequences of these S-OIV peptides would not affect or partially affect memory T-cell responses. These findings suggest that without protective antibody responses, individuals vaccinated against seasonal influenza A may still benefit from preexisting cross-reactive memory CD4 T cells reducing their susceptibility to S-OIV infection.
Viral Protein Determinants of Lassa Virus Entry and Release from Polarized Epithelial Cells
Authors: Schlie Katrin , Maisa Anna , Freiberg Fabian , Groseth Allison , Strecker Thomas , Garten Wolfgang
Published: January 2010

The epithelium plays a key role in the spread of Lassa virus. Transmission from rodents to humans occurs mainly via inhalation or ingestion of droplets, dust, or food contaminated with rodent urine. Here, we investigated Lassa virus infection in cultured epithelial cells and subsequent release of progeny viruses. We show that Lassa virus enters polarized Madin-Darby canine kidney (MDCK) cells mainly via the basolateral route, consistent with the basolateral localization of the cellular Lassa virus receptor α-dystroglycan. In contrast, progeny virus was efficiently released from the apical cell surface. Further, we determined the roles of the glycoprotein, matrix protein, and nucleoprotein in directed release of nascent virus. To do this, a virus-like-particle assay was developed in polarized MDCK cells based on the finding that, when expressed individually, both the glycoprotein GP and matrix protein Z form virus-like particles. We show that GP determines the apical release of Lassa virus from epithelial cells, presumably by recruiting the matrix protein Z to the site of virus assembly, which is in turn essential for nucleocapsid incorporation into virions.
Phosphorylation-Mediated Negative Regulation of RIG-I Antiviral Activity
Authors: Gack Michaela U. , Nistal-Villán Estanislao , Inn Kyung-Soo , García-Sastre Adolfo , Jung Jae U.
Published: January 2010

Recognition of invading viruses by the host is elicited by cellular sensors which trigger signaling cascades that lead to type I interferon (IFN) gene expression. Retinoic acid-inducible gene I (RIG-I) has emerged as a key receptor for the detection of viral RNA in the cytosol, inducing IFN-mediated innate immune responses to limit viral replication through its interaction with MAVS (also called IPS-1, CARDIF, or VISA). Upon the recognition of viral RNA, the Lys-172 residue of RIG-I undergoes ubiquitination induced by tripartite motif protein 25 (TRIM25), an essential protein for antiviral signal transduction. Here we demonstrate that phosphorylation represents another regulatory mechanism for RIG-I-mediated antiviral activity. Using protein purification and mass spectrometry analysis, we identified three phosphorylation sites in the amino-terminal caspase recruitment domains (CARDs) of RIG-I. One of these residues, Thr-170, is located in close proximity to Lys-172, and we speculated that its phosphorylation may affect Lys-172 ubiquitination and functional activation of RIG-I. Indeed, a RIG-I mutant carrying a phosphomimetic Glu residue in place of Thr-170 loses TRIM25 binding, Lys-172 ubiquitination, MAVS binding, and downstream signaling ability. This suggests that phosphorylation of RIG-I at Thr-170 inhibits RIG-I-mediated antiviral signal transduction. Immunoblot analysis with a phospho-specific antibody showed that the phosphorylation of the RIG-I Thr-170 residue is present under normal conditions but rapidly declines upon viral infection. Our results indicate that Thr-170 phosphorylation and TRIM25-mediated Lys-172 ubiquitination of RIG-I functionally antagonize each other. While Thr-170 phosphorylation keeps RIG-I latent, Lys-172 ubiquitination enables RIG-I to form a stable complex with MAVS, thereby inducing IFN signal transduction.
Identification of Host Factors Involved in Borna Disease Virus Cell Entry through a Small Interfering RNA Functional Genetic Screen
Authors: Clemente Roberto , Sisman Eugene , Aza-Blanc Pedro , de la Torre Juan C.
Published: January 2010

Borna disease virus (BDV), the prototypic member of theBornaviridaefamily, within the orderMononegavirales, is highly neurotropic and constitutes an important model system for the study of viral persistence in the central nervous system (CNS) and associated disorders. The virus surface glycoprotein (G) has been shown to direct BDV cell entry via receptor-mediated endocytosis, but the mechanisms governing cell tropism and propagation of BDV within the CNS are unknown. We developed a small interfering RNA (siRNA)-based screening to identify cellular genes and pathways that specifically contribute to BDV G-mediated cell entry. Our screen relied on silencing-mediated increased survival of cells infected with rVSVΔG*/BDVG, a cytolytic recombinant vesicular stomatitis virus expressing BDV G that mimics the cell tropism and entry pathway of bona fide BDV. We identified 24 cellular genes involved in BDV G-mediated cell entry. Identified genes are known to participate in a broad range of distinct cellular functions, revealing a complex process associated with BDV cell entry. The siRNA-based screening strategy we have developed should be applicable to identify cellular genes contributing to cell entry mediated by surface G proteins of other viruses.
Measles Virus Selectively Blind to Signaling Lymphocytic Activation Molecule (SLAM; CD150) Is Attenuated and Induces Strong Adaptive Immune Responses in Rhesus Monkeys
Authors: Leonard Vincent H. J. , Hodge Gregory , Reyes-del Valle Jorge , McChesney Michael B. , Cattaneo Roberto
Published: January 2010

The signaling lymphocytic activation molecule (SLAM; CD150) is the immune cell receptor for measles virus (MV). To assess the importance of the SLAM-MV interactions for virus spread and pathogenesis, we generated a wild-type IC-B MV selectively unable to recognize human SLAM (SLAM-blind). This virus differs from the fully virulent wild-type IC-B strain by a single arginine-to-alanine substitution at amino acid 533 of the attachment protein hemagglutinin and infects cells through SLAM about 40 times less efficiently than the isogenic wild-type strain.Ex vivo, this virus infects primary lymphocytes at low levels regardless of SLAM expression. When a group of six rhesus monkeys (Macaca mulatta) was inoculated intranasally with the SLAM-blind virus, no clinical symptoms were documented. Only one monkey had low-level viremia early after infection, whereas all the hosts in the control group had high viremia levels. Despite minimal, if any, viremia, all six hosts generated neutralizing antibody titers close to those of the control monkeys while MV-directed cellular immunity reached levels at least as high as in wild-type-infected monkeys. These findings prove formally that efficient SLAM recognition is necessary for MV virulence and pathogenesis. They also suggest that the selectively SLAM-blind wild-type MV can be developed into a vaccine vector.
An Ascovirus-Encoded RNase III Autoregulates Its Expression and Suppresses RNA Interference-Mediated Gene Silencing
Authors: Hussain Mazhar , Abraham Alexander M. , Asgari Sassan
Published: January 2010

RNase III proteins play vital roles in processing of several types of RNA molecules and gene silencing. Recently, it has been discovered that some plant and animal viruses encode RNase III-like proteins as well. Genome sequencing of four virus species belonging to the
Ascoviridae
family has revealed sequence conservation of an RNase III open reading frame among the viruses. These have not been explored in ascoviruses, and therefore their role in host-virus interaction is unknown. Here, we confirmed expression of
Heliothis virescens ascovirus
(HvAV-3e) open reading frame 27 (
orf27
) that encodes an RNase III-like protein after infection and demonstrated dsRNA specific endoribonuclease activity of the encoded protein. Analysis of the expression patterns of
orf27
in virus-infected insect cells and a bacterial expression system revealed autoregulation of this protein over time. Moreover, HvAV-3e RNase III was found essential for virus DNA replication and infection using RNA interference (RNAi)-mediated gene silencing. In addition, using green fluorescent protein gene as a marker, we provide evidence that RNase III is involved in the suppression of gene silencing. To our knowledge, this is the first insect virus-encoded RNase III described and shown to suppress host cell RNAi defense mechanism.
Poly(A) at the 3′ End of Positive-Strand RNA and VPg-Linked Poly(U) at the 5′ End of Negative-Strand RNA Are Reciprocal Templates during Replication of Poliovirus RNA
Authors: Steil Benjamin P. , Kempf Brian J. , Barton David J.
Published: January 2010

A 3′ poly(A) tail is a common feature of picornavirus RNA genomes and the RNA genomes of many other positive-strand RNA viruses. We examined the manner in which the homopolymeric poly(A) and poly(U) portions of poliovirus (PV) positive- and negative-strand RNAs were used as reciprocal templates during RNA replication. Poly(A) sequences at the 3′ end of viral positive-strand RNA were transcribed into VPg-linked poly(U) products at the 5′ end of negative-strand RNA during PV RNA replication. Subsequently, VPg-linked poly(U) sequences at the 5′ ends of negative-strand RNA templates were transcribed into poly(A) sequences at the 3′ ends of positive-strand RNAs. The homopolymeric poly(A) and poly(U) portions of PV RNA products of replication were heterogeneous in length and frequently longer than the corresponding homopolymeric sequences of the respective viral RNA templates. The data support a model of PV RNA replication wherein reiterative transcription of homopolymeric templates ensures the synthesis of long 3′ poly(A) tails on progeny RNA genomes.
Potentiometry in gas phase
Authors: Janata Jiří
Published: January 2010

In order to yield analytically useful information every potentiometric measurement requires stable and reproducible reference potential. That requirement has to be satisfied for potentiometry performed in liquid or gas phase alike, although two fundamentally different mechanisms lead to formation of the measurable cell voltage. It is shown that the Fermi level of silicon used in insulated gate field-effect transistors (IGFET) provides an exceptionally stable and robust reference potential. A semi-quantitative dependence of IGFET output on partial pressure of the analyte gas is presented.
Osteonecrosis of the jaw: a rare and devastating side effect of bisphosphonates
Authors: Ryan P , Saleh I , Stassen L F A
Published: January 2010

Evidence has emerged that bisphosphonate use in cancer patients is associated with osteonecrosis of the jaw. This form of osteonecrosis has been termed bisphosphonate induced osteonecrosis of the jaw (BIONJ). BIONJ is commonly precipitated by a tooth extraction in patients treated with long term, potent, high dose intravenous bisphosphonates for the management of myeloma, breast or prostate cancer. The overall prevalence of BIONJ is about 5% in patients with these malignancies. Current evidence shows that the risk of BIONJ in non-cancerous patients, such as those with osteoporosis, is very low and appears to be comparable with that of the general population. Prescribing physicians need to encourage cancer patients to see their dentists before the initiation of bisphosphonate treatment, and regularly thereafter.
Management of thyroid disorders in primary care: challenges and controversies
Authors: Todd C H
Published: January 2010

Thyroid diseases are common, and most can be safely and effectively managed in primary care. Two of the most common reasons for thyroid function testing are fatigue and obesity, but the vast majority of affected patients do not have hypothyroidism. There is no plausible basis for the assertion that hypothyroidism commonly occurs despite normal thyroid function tests. In primary hypothyroidism all patients, except the elderly and those with ischaemic heart disease, can safely be started on a full replacement dose of thyroxine; the aim is to restore thyroid stimulating hormone (TSH) to normal. Triiodothyronine (T3) has no role in the treatment of primary hypothyroidism. Subclinical thyroid disease should not be treated except in certain well defined situations. Its main importance lies in the increased risk of progression to overt thyroid disease. The development of hyperthyroidism is easily overlooked, and it is important to maintain a high index of suspicion, especially in the elderly. The most common causes are Graves’ disease and thyroiditis (especially postpartum), and in the elderly toxic nodular goitre and amiodarone. Patients taking amiodarone should have their thyroid function checked every 6 months. Patients with overt hyperthyroidism should be referred for specialist management; β-blockers and sometimes anti-thyroid drugs may be initiated in primary care. Most thyroid nodules, especially those detected incidentally on ultrasound scanning, are benign. Indications for referral include newly occurring nodules >1cm in diameter, painful nodules, and nodules that are increasing in size.
Primary immunodeficiency diseases: a practical guide for clinicians
Authors: Turvey S E , Bonilla F A , Junker A K
Published: January 2010

Primary immunodeficiency diseases (PIDs) are genetically determined disorders of the immune system resulting in greatly enhanced susceptibility to infectious disease, autoimmunity and malignancy. While individual PIDs are rare, as a group, it is estimated that between 1:2000 and 1:10 000 live births are affected by a PID. Moreover, PIDs can present at any age from birth to adulthood, posing a considerable challenge for the practising physician to know when and how to work-up a patient for a possible immune defect. In this review, we outline the basic organisation of the human immune system and the types of infections that occur when elements of the immune system are dysfunctional. Importantly, we provide practical guidelines for identifying patients who should be referred for assessment of possible immunodeficiency and an overview of screening investigations and effective therapeutic options available for these patients.
Management of the first seizure: an evidence based approach
Authors: Seneviratne U
Published: January 2010

The first seizure is more common than epilepsy. A detailed history is vital in the assessment in order to reveal unreported minor seizures such as myoclonic jerks, simple partial seizures and absences in the past. The first seizure could be provoked or unprovoked. Provoked seizures have a lower risk or recurrence. Electroencephalogram (EEG) studies and neuroimaging are essential components in the diagnostic work up. Abnormal neurological status and abnormal EEG are the most significant predictors of seizure recurrence. Antiepileptic drug (AED) treatment after the first seizure significantly reduces seizure recurrence rate in the first 2 years. However it does not appear to change the long term outlook. There are some patients who would benefit from AED treatment after the first seizure. This paper discusses the current evidence on this multifaceted clinical problem which would help formulate a rational management plan.
FAST-TIA: a prospective evaluation of a nurse-led anterior circulation TIA clinic
Authors: Banerjee S , Natarajan I , Biram R , Sutton K , Ekeng G , Ames D , Chataway J
Published: January 2010

Background

Transient ischaemic attacks (TIAs) carry a significant early risk of stroke. New national guidelines state patients should be seen within 7 days of the incident, with higher-risk patients being seen within 24 h. Meeting these targets across the NHS poses a significant challenge. A novel approach to TIA assessment has been developed using a nurse-led rapid-access anterior circulation TIA clinic.

Methods

This was a prospective evaluation of all patients attending the FAST-TIA clinic between November 2003 and December 2006. Diagnostic yield of neurovascular events among patients seen through the TIA service and median time from referral to assessment and from event to assessment were measured.

Results

282 patients were eligible for investigation, and seen through the clinic over a period of 38 months. A vascular event was diagnosed in 242 (86%). TIA was diagnosed in 133 (55%), minor ischaemic stroke in 77 (32%), haemorrhagic stroke in three (1%), and an ocular event in 29 (12%). Median time from referral to assessment was 3 days (interquartile range (IQR) 1–7), and from event to assessment it was 7 days (IQR 3–18). 34% of patients were seen within 24 h of referral.

Conclusions

This model has a high diagnostic rate of 86% vascular events, significantly higher than current national averages of ∼55%. Current national guidelines for early assessment of patients (published subsequent to this study) are achievable using this service. The FAST-TIA model is an easily reproducible and pragmatic method of improving the diagnostic yield of TIA services, while keeping within national targets.
Role of medical intervention in slowing the growth of small abdominal aortic aneurysms
Authors: Cooper D G , King J A , Earnshaw J J
Published: January 2010

Abdominal aortic aneurysm is a common—but preventable—cause of death in elderly men; 4% of men at the age of 65 years have an aorta >3 cm in diameter. Continued expansion runs the risk of aneurysm rupture, a condition that is fatal in all but 15% of individuals. A national screening programme has commenced that aims to reduce the number of deaths from aneurysm rupture by 50%. The programme will detect a large number of men with a small aneurysm who are not in imminent danger of rupture, but who will join a regular ultrasound programme of surveillance. If the aneurysm expansion rate could be reduced, fewer men would be at risk of aneurysm rupture, and fewer would need elective aneurysm repair. A considerable amount is known about the pathophysiology of aneurysm growth. Exploring pharmacological means to delay or reduce aneurysm growth could make a considerable contribution to any screening programme. A number of case control studies have suggested that some antihypertensive drugs, non-steroidal anti-inflammatory drugs, antibiotics, and statins may reduce aneurysm growth rates. Data from controlled studies have provided less secure conclusions. Use of these medications, together with lifestyle modification such as stopping smoking, could become standard advice to men with a small aortic aneurysm. Further studies of novel agents and larger controlled trials of existing drugs are warranted.
Endobronchial stenting in the management of large airway pathology
Authors: Ranu H , Madden B P
Published: January 2010

Endobronchial interventions including the deployment of endobronchial stents have a clear role in the management of central airway problems. The use of endobronchial stents has rapidly increased since the first airway stent was developed in the 1960s and with the subsequent manufacture of improved silicone and metallic stents. They provide effective relief for symptoms of intrinsic and extrinsic airway obstruction secondary to a wide range of pathologies including lung cancer, lymphoma, thyroid carcinoma and benign disease such as tracheal strictures and tracheobronchomalacia. Endobronchial stents can also seal defects within the airway including malignant broncho-oesophageal fistulae and posterior wall tracheal tears. They can be placed safely under conscious sedation at flexible bronchoscopy or under general anaesthetic at rigid bronchoscopy. Rigid bronchoscopy under general anaesthesia provided by a multidisciplinary team is safe with few contraindications. Complications of endobronchial stents include infection, granulation tissue formation and metallic stent fracture sometimes requiring removal, although serious life-threatening complications are very rare. Increasing numbers of patients are being referred to specialist centres for airway intervention. This article reviews the history of endobronchial stents, the different stents available, and the indications, outcomes and complications involved in deploying endobronchial stents.
A Rapid Simple Long-Term Toxicity Assay for Aquatic Contaminants Using the Nematode Panagrellus redivivus
Authors: Samoiloff M. R. , Schulz S. , Jordan Y. , Denich K. , Arnott E.
Published: January 2010

Two protocols using the free-living nematode Panagrellus redivivus to determine the developmental or mutagenic effects of environmental contaminants were tested. Fifteen known carcinogens or mutagens, six suspected carcinogens, and seven heavy metal compounds were tested at concentrations ranging from 10−8 to 10−3 mol/L. A developmental assay using frequency of completion of the three postembryonic molts detected toxic effects of 24 of the 28 tested agents, while survival was decreased in only 10 of the 28 agents. Mutagenesis was detected in 12 of the known carcinogens, three of the suspected carcinogens, and one heavy metal compound. Therefore, assays are suitable for detection of long-term toxicity of contaminants in aquatic environments.Key words: Panagrellus, nematode, carcinogens, mutagens, developmental assay, toxicology assay
MONTE CARLO SIMULATION OF SOIL MOISTURE EFFECTS ON ANTI-TANK LANDMINES DETECTION BY NEUTRON BACKSCATTERING TECHNIQUE
Authors: MOWLAWI ALI ASGHAR , YAZDANI MAJED
Published: January 2010

The detection of landmines using available technologies is a time consuming, expensive, and extremely dangerous job, so that there is a need for technological breakthroughs in this field. One of the safest and most effective technologies to landmine and explosive detection is the neutron backscattering technique. The slowing-down of fast neutrons to the thermal energy is a direct measure of the concentration of hydrogen, one of the main elements present in explosive materials. The elastic scattering of fast neutrons is affected by the strong resonances in the cross-section of the three other elements of explosives: nitrogen, oxygen, and carbon. In this work, Monte Carlo estimations of the soil moisture effects on landmine detection are presented.
ONE-DIMENSIONAL LONG-RANGE FERROMAGNETIC ISING MODEL UNDER WEAK AND SPARSE EXTERNAL FIELD
Authors: KERIMOV AZER
Published: January 2010

We consider the one-dimensional ferromagnetic Ising model with very long range interaction under weak and sparse biased external field and prove that at sufficiently low temperatures, the model has a unique limiting Gibbs state.
ENERGY TRANSFER FROM POLY(VINYLCARBAZOLE) TO A CHIRAL CONJUGATED POLYMER
Authors: ZHANG X. , HUANG H. , QIAO Y. , XU C. X. , CHENG Y. X. , CUI Y. P.
Published: January 2010

The energy transfer between a chiral conjugated polymer P1 which incorporates (R)-2, 2′-bisbutoxy-1, 1′-binaphthyl and 1, 4-divinyl-2, 3-bisbutoxy-naphthalene moieties and poly(vinylcarbazole) (PVK) has been studied by using the steady-state and time-resolved photoluminescence (PL) spectroscopy. The absorption spectrum of P1 has good overlap with the PL spectrum of PVK. The blend films of PVK doped with P1 only emitted the light originating from P1, although the excitation wavelength was selected at 340 nm which corresponds to the peak absorption of PVK. The decay time of these two materials varied with the weight ratios of PVK to P1. The energy transfer from P1 and PVK investigated in detail.
OBSERVATION OF FERROMAGNETISM IN Mn-DOPED NANO ZnO
Authors: RAJKUMAR N. , RAMACHANDRAN K.
Published: January 2010

Ferromagnetism (FM) at room temperature in nano ZnO:Mn is closely monitored here for very low concentration of Mn , as there are conflicting reports on FM, in the uniformly doped system.
FIRST-PRINCIPLES STUDIES ON THE ELECTRONIC STRUCTURE OF LuPd2Si2
Authors: JEONG T.
Published: January 2010

The electronic band structure of LuPd 2 Si 2 was studied based on the density functional theory within local density approximation and fully relativistic schemes. The Lu 4f states are completely filled and have flat bands around -5.0 eV. The fully relativistic band structure scheme shows that spin–orbit coupling splits the 4f states into two manifolds, the 4f7/2 and the 4f5/2 multiplet.
SOME ASPECTS OF THE NON-PERTURBATIVE RENORMALIZATION OF THE φ4 MODEL
Authors: KAUPUŽS J.
Published: January 2010

A non-perturbative renormalization of the φ4 model is considered. First, we integrate out only a single pair of conjugated modes with wave vectors ±q. Then, we are looking for the RG equation which would describe the transformation of the Hamiltonian under the integration over a shell Λ - d Λ < k < Λ, where dΛ → 0. We show that the known Wegner–Houghton equation is consistent with the assumption of a simple superposition of the integration results for ±q. The renormalized action can be expanded in powers of the φ4 coupling constant u in the high temperature phase at u → 0. We compare the expansion coefficients with those exactly calculated by the diagrammatic perturbative method and find some inconsistency. It causes a question in which sense the Wegner–Houghton equation is really exact.
EFFECT OF PSEUDOMORPHIC MULTIPLE QUANTUM WELL LAYERS ON CHARACTERISTICS OF UNCOOLED ELECTROLUMINESCENT DIODE
Authors: HAN JAE-HO , LHEE ZAIL , PARK SUNG-WOONG
Published: January 2010

We have fabricated and characterized the uncooled light emitting device having a pseudomorphic structure of multiple quantum wells. The effect of numbers of compressively strained quantum well layers on the semiconductor diode laser characteristics was experimentally demonstrated, depending on room and high temperatures. In addition to the automatically embedded absorptive grating which can reduce the epitaxial growth step, the laser performance can be optimized for both threshold current and differential slope efficiency when the quantum well numbers are reduced to five layers for optical communication systems.
COLLISION-DEPENDENT ATOM TUNNELING RATE — BOSE–EINSTEIN CONDENSATES IN DOUBLE AND MULTIPLE WELL TRAPS
Authors: DE OLIVEIRA M. C. , DA CUNHA B. R.
Published: January 2010

The overlap of localized wave functions in a two-mode approximation leads to interaction (cross-collision) between ultra-cold atoms trapped in distinct sites of a double-well potential. We show that this interaction can significantly change the atom tunneling rate for special trap configurations resulting in an effective linear Rabi regime of population oscillation between the trap wells. In this sense, we demonstrate that cross-collisional effects can significantly extend the validity of the two-mode model approach allowing it to be alternatively employed to explain the recently observed increase of tunneling rates due to nonlinear interactions. Moreover, we investigate the extension for ultra-cold atoms trapped in an optical lattice. Control over the cross-collisional terms, obtained through manipulation of the optical trapping potential, can be used as an engineering tool to study many-body physics.
ORBITAL ORDERINGS AND OPTICAL CONDUCTIVITY INCs2AgF4
Authors: ZHANG MIN-PING , QIAN YU-MIN , WANG GUANG-TAO
Published: January 2010

The Jahn–Teller (JT) distortion induced orbital order and optical-conductivity in Cs2AgF4are investigated by first-principle calculations. Cs2AgF4contains 4d9Ag2+, similar to 3d9Cu2+of La2CuO4. Although Cs2AgF4is an isoelectronic analogue of La2CuO4, their magnetisms are radically different: La2CuO4is antiferromagnetism (AFM), while Cs2AgF4is proposed to be ferromagnetism (FM) based on recent neutron scattering data. The great difference can be understood from the JT distortions in the AgF6octahedron, which favors the formation of staggered orbital order of dz2-x2and dz2-y2. Such orbital order favors FM state, according to Goodenough–Kanamori Rules. We find when the JT distortion is larger than 0.03, the ground state of Cs2AgF4is AFM. This antiferromagnetism might induce superconductivity, just as La2CuO4. In order to confirm such orbital order of Ag , we present the calculated optical-conductivity, which could be examined by experiment.
CAUSAL FREQUENCY-LINEAR ATTENUATION ALGORITHM FOR TIME DOMAIN PROBLEMS
Authors: MCDONALD B. EDWARD
Published: January 2010

Attenuation which is linear in frequency (as opposed to quadratic as for laminar viscosity) occurs in porous media wave propagation and biomedical applications. Straightforward use of Fourier transforms for frequency-linear attenuation violates causality. We give a causal time domain algorithm with numerical stability criteria and verify its accuracy. For acoustic wave propagation in ocean sediment, the algorithm results in a mild increase of phase speed with frequency as a result of the Kramers–Kronig relation. The algorithm gives results in good agreement with in situ data for sandy sediment.
COMPUTATION OF THE FLOW AND NEAR SOUND FIELDS OF A FREE SURFACE PIERCING CYLINDER
Authors: AVITAL ELDAD J. , YU GUANGXU , WILLIAMS JOHN
Published: January 2010

The near sound field generated due to a vertically mounted circular cylinder piercing a free surface in shallow water, is studied computationally using the Large Eddy Simulation (LES) approach and the sound wave equation. The flow is simulated in both the air and water phases. The interface surface is allowed to move and is simulated using the Volume of Fluid technique. The pressure distribution over the cylinder is fed back into the sound wave equation to calculate the near field. The interface surface is modeled as a zero pressure surface in the acoustic calculation and the bottom is taken as having infinite impedence modeling the case of a rigid floor. Two of acoustic calculations methods are used. In the first method, the interface surface is assumed to be fixed and the wave equation is solved in the frequency domain in a post-processing stage. In the second method, the evolution of the interface surface is taken into account and the wave equation is simulated simultaneously with the LES. Both solutions are analyzed and compared to show that the interface surface acts as a strong damper to the low frequency sound by damping the vortex Von Karman rollers as well as causing the low frequency component to be nonradiative. The variation of the near sound field with the water depth and Froude number is investigated and the propagation and damping characteristics are analyzed.
SPECTRAL ELEMENT METHOD FOR ACOUSTIC PROPAGATION PROBLEMS BASED ON LINEARIZED EULER EQUATIONS
Authors: ZHANG RONGXIN , QIN GUOLIANG , ZHU CHANGYUN
Published: January 2010

A Chebyshev spectral element approximation of acoustic propagation problems based on linearized Euler equations is introduced, and the numerical approach is based on spectral elements in space with first-order Clayton–Engquist–Majda absorbing boundary conditions and implicit Newmark method in time. An initial perturbation problem has been solved to test the accuracy and stability of the numerical method. Then the sound propagation by source terms is also studied, including the radiation of a monopole and dipolar source in both stationary medium and uniform mean flow. The numerical simulation leads to good results in both accuracy and stability. Compared with the analytical solutions, the numerical results show the advantages in spectral accuracy even with relatively fewer grid points. Moreover, the implicit Newmark method in time marching also presents its superiority in stability. Finally, a problem of sound propagation in pipes is simulated as well.
Stock Returns and Volatility: Evidence from Select Emerging Markets
Authors: Arora Ravinder Kumar , Das Himadri , Jain Pramod Kumar
Published: January 2010

This paper investigates the behavior of stock returns and volatility in 10 emerging markets and compares them with those of developed markets under different measures of frequency (daily, weekly, monthly and annual) over the period January 1, 2002 to December 31, 2006. The ratios of mean return to volatility for emerging markets are found to be higher than those of developed markets. Sample statistics for stock returns of all emerging and developed markets indicate that return distributions are not normal and return volatility shows clustering. In most cases, GARCH (1, 1) specification is adequate to describe the stock return volatility. The significant lag terms in the mean equation of GARCH specification depend on the frequency of the return data. The presence of leverage effect in volatility behavior is examined using the TAR-GARCH model and the evidence indicates that is not present across all markets under all measures of frequency. Its presence in different markets depends on the measure of frequency of stock return data.
Hedging and Optimal Hedge Ratios for International Index Futures Markets
Authors: Lee Cheng-Few , Wang Kehluh , Chen Yan Long
Published: January 2010

This empirical study utilizes four static hedging models (OLS Minimum Variance Hedge Ratio, Mean-Variance Hedge Ratio, Sharpe Hedge Ratio, and MEG Hedge Ratio) and one dynamic hedging model (bivariate GARCH Minimum Variance Hedge Ratio) to find the optimal hedge ratios for Taiwan Stock Index Futures, S&P 500 Stock Index Futures, Nikkei 225 Stock Index Futures, Hang Seng Index Futures, Singapore Straits Times Index Futures, and Korean KOSPI 200 Index Futures. The effectiveness of these ratios is also evaluated. The results indicate that the methods of conducting optimal hedging in different markets are not identical. However, the empirical results confirm that stock index futures are effective direct hedging instruments, regardless of hedging schemes or hedging horizons.
An Analysis of China's Stock Market in the First 10 Years
Authors: Cheng Siwei
Published: January 2010

The purpose of this paper is to provide a systematic analysis of the development of the Chinese stock market in the first 10 years. It can be a lesson to both researchers and investors on China's stock market. In this paper, the author first shares his own experience from involvement in policy making and regulation inspections in developing China's stock market. Then, based on observations at the market as well as academic research findings that he conducted with his colleagues, the author discusses eight major problems that should be addressed in order to build a mature stock market in China to support the sustainable development of China's economy.
Investment Preference and Strategies of Foreign Institutional Investors Across Different Industries in Taiwan
Authors: Chen Mei-Ling , Lin Fu-Lai , Hung Mei-Chin , Wang Kai-Li
Published: January 2010

This paper investigates the investment preference of foreign institutional investors across different industries in Taiwanese stock market. By employing the idea of Fama and French (1992) three-factor model with investment strategy, the investment preference is a function of beta value, company size, book-market ratio and investment strategy. Our empirical results find that foreign institutional investors in all five industries adopt momentum strategies in their investment preference. Next, in each industry, investment preference has a long-run equilibrium relationship with beta value, company size, book-market ratio, and investment strategy. Moreover, in the electronic, financial, and steel industries, foreign institutional investors' investment preference has corrective power in the short-run. Further, the results of the Granger causality test reveal that the investment preference has a uni-directional leading relationship with beta value in the financial and textile industries. While in case of the steel industry, investment preference and beta value have a bi-directional causal feedback relationship. Industries where company size leads investment preference include electronics, finance, and steel. Book-market ratio leads investment preference only in the textile industry. Generally speaking, in each industry, company size is among the predominant factors that foreign institutional investors take into account when making decisions. The influences of beta value and investment strategy on investment preference do not appear significant. That is, the investment strategy under consideration does not make a difference for investment preference.
Certification of bounds on expressions involving rounded operators
Authors: Daumas Marc , Melquiond Guillaume
Published: January 2010

Gappa is a tool designed to formally verify the correctness of numerical software and hardware. It uses interval arithmetic and forward error analysis to bound mathematical expressions that involve rounded as well as exact operators. It then generates a theorem and its proof for each verified enclosure. This proof can be automatically checked with a proof assistant, such as Coq or HOL Light. It relies on a large companion library of facts that we have developed. This Coq library provides theorems dealing with addition, multiplication, division, and square root, for both fixed- and floating-point arithmetics. Gappa uses multiple-precision dyadic fractions for the endpoints of intervals and performs forward error analysis on rounded operators when necessary. When asked, Gappa reports the best bounds it is able to reach for a given expression in a given context. This feature can be used to identify where the set of facts and automatic techniques implemented in Gappa becomes insufficient. Gappa handles seamlessly additional properties expressed as interval properties or rewriting rules in order to establish more intricate bounds. Recent work showed that Gappa is suited to discharge proof obligations generated for small pieces of software. They may be produced by third-party tools and the first applications of Gappa use proof obligations written by designers or obtained from traces of execution.
Verified just-in-time compiler on x86
Authors: Myreen Magnus O.
Published: January 2010

This paper presents a method for creating formally correct just-in-time (JIT) compilers. The tractability of our approach is demonstrated through, what we believe is the first, verification of a JIT compiler with respect to a realistic semantics of self-modifying x86 machine code. Our semantics includes a model of the instruction cache. Two versions of the verified JIT compiler are presented: one generates all of the machine code at once, the other one is incremental i.e. produces code on-demand. All proofs have been performed inside the HOL4 theorem prover.
Structuring the verification of heap-manipulating programs
Authors: Nanevski Aleksandar , Vafeiadis Viktor , Berdine Josh
Published: January 2010

Most systems based on separation logic consider only restricted forms of implication or non-separating conjunction, as full support for these connectives requires a non-trivial notion of variable context, inherited from the logic of bunched implications (BI). We show that in an expressive type theory such as Coq, one can avoid the intricacies of BI, and support full separation logic very efficiently, using the native structuring primitives of the type theory.

Our proposal uses reflection to enable equational reasoning about heaps, and Hoare triples with binary postconditions to further facilitate it. We apply these ideas to Hoare Type Theory, to obtain a new proof technique for verification of higher-order imperative programs that is general, extendable, and supports very short proofs, even without significant use of automation by tactics. We demonstrate the usability of the technique by verifying the fast congruence closure algorithm of Nieuwenhuis and Oliveras, employed in the state-of-the-art Barcelogic SAT solver.
Pure subtype systems
Authors: Hutchins DeLesley S.
Published: January 2010

This paper introduces a new approach to type theory called
pure subtype systems
. Pure subtype systems differ from traditional approaches to type theory (such as pure type systems) because the theory is based on subtyping, rather than typing. Proper types and typing are completely absent from the theory; the subtype relation is defined directly over objects. The traditional typing relation is shown to be a special case of subtyping, so the loss of types comes without any loss of generality.

Pure subtype systems provide a uniform framework which seamlessly integrates subtyping with dependent and singleton types. The framework was designed as a theoretical foundation for several problems of practical interest, including mixin modules, virtual classes, and feature-oriented programming.

The cost of using pure subtype systems is the complexity of the meta-theory. We formulate the subtype relation as an abstract reduction system, and show that the theory is sound if the underlying reductions commute. We are able to show that the reductions commute locally, but have thus far been unable to show that they commute globally. Although the proof is incomplete, it is ``close enough'' to rule out obvious counter-examples. We present it as an open problem in type theory.
Programming with angelic nondeterminism
Authors: Bodik Rastislav , Chandra Satish , Galenson Joel , Kimelman Doug , Tung Nicholas , Barman Shaon , Rodarmor Casey
Published: January 2010

Angelic nondeterminism can play an important role in program development. It simplifies specifications, for example in deriving programs with a refinement calculus; it is the formal basis of regular expressions; and Floyd relied on it to concisely express backtracking algorithms such as N-queens.

We show that angelic nondeterminism is also useful during the development of deterministic programs. The semantics of our angelic operator are the same as Floyd's but we use it as a substitute for yet-to-be-written deterministic code; the final program is fully deterministic. The angelic operator divines a value that makes the program meet its specification, if possible. Because the operator is executable, it allows the programmer to test incomplete programs: if a program has no safe execution, it is already incorrect; if a program does have a safe execution, the execution may reveal an implementation strategy to the programmer.

We introduce refinement-based angelic programming, describe our embedding of angelic operators into Scala, report on our implementation with bounded model checking, and describe our experience with two case studies. In one of the studies, we use angelic operators to modularize the Deutsch-Schorr-Waite (DSW) algorithm. The modularization is performed with the notion of a parasitic stack, whose incomplete specification was instantiated for DSW with angelic nondeterminism.
Monads in action
Authors: Filinski Andrzej
Published: January 2010

In functional programming, monadic characterizations of computational effects are normally understood denotationally: they describe how an effectful program can be systematically expanded or translated into a larger, pure program, which can then be evaluated according to an effect-free semantics. Any effect-specific operations expressible in the monad are also given purely functional definitions, but these definitions are only directly executable in the context of an already translated program. This approach thus takes an inherently Church-style view of effects: the nominal meaning of every effectful term in the program depends crucially on its type.

We present here a complementary, operational view of monadic effects, in which an effect definition directly induces an imperative behavior of the new operations expressible in the monad. This behavior is formalized as additional operational rules for only the new constructs; it does not require any structural changes to the evaluation judgment. Specifically, we give a small-step operational semantics of a prototypical functional language supporting programmer-definable, layered effects, and show how this semantics naturally supports reasoning by familiar syntactic techniques, such as showing soundness of a Curry-style effect-type system by the progress+preservation method.
Higher-order multi-parameter tree transducers and recursion schemes for program verification
Authors: Kobayashi Naoki , Tabuchi Naoshi , Unno Hiroshi
Published: January 2010

We introduce higher-order, multi-parameter, tree transducers (HMTTs, for short), which are kinds of higher-order tree transducers that take input trees and output a (possibly infinite) tree. We study the problem of checking whether the tree generated by a given HMTT conforms to a given output specification, provided that the input trees conform to input specifications (where both input/output specifications are regular tree languages). HMTTs subsume higher-order recursion schemes and ordinary tree transducers, so that their verification has a number of potential applications to verification of functional programs using recursive data structures, including resource usage verification, string analysis, and exact type-checking of XML-processing programs.

We propose a sound but incomplete verification algorithm for the HMTT verification problem: the algorithm reduces the verification problem to a model-checking problem for higher-order recursion schemes extended with finite data domains, and then uses (an extension of)Kobayashi's algorithm for model-checking recursion schemes. While the algorithm is incomplete (indeed, as we show in the paper, the verification problem is undecidable in general), it is sound and complete for a subclass of HMTTs called
linear HMTTs
. We have applied our HMTT verification algorithm to various program verification problems and obtained promising results.