bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting
In Vitro
Antibacterial Efficacy across Experimental Designs with a Semimechanistic Pharmacokinetic-Pharmacodynamic Model
Authors: Nielsen Elisabet I. , Cars Otto , Friberg Lena E.
Published: February 2011

We have previously described a general semimechanistic pharmacokinetic-pharmacodynamic (PKPD) model that successfully characterized the time course of antibacterial effects seen in bacterial cultures when exposed to static concentrations of five antibacterial agents of different classes. In this PKPD model, the total bacterial population was divided into two subpopulations, one growing drug-susceptible population and one resting drug-insensitive population. The drug effect was included as an increase in the killing rate of the drug-susceptible bacteria with a maximum-effect (
E
max
) model. The aim of the present study was to evaluate the ability of this PKPD model to describe and predict data from
in vitro
experiments with dynamic concentration-time profiles. Dynamic time-kill curve experiments were performed by using an
in vitro
kinetic system, where cultures of
Streptococcus pyogenes
were exposed to benzylpenicillin, cefuroxime, erythromycin, moxifloxacin, or vancomycin using different starting concentrations (2 and 16 times the MIC) and elimination conditions (human half-life, reduced half-life, and constant concentrations). The PKPD model was applied, and the observations for the static as well as dynamic experiments were compared to model predictions based on parameter estimation using (i) static data, (ii) dynamic data, and (iii) combined static and dynamic data. Differences in experimental settings between static and dynamic experiments did not affect the growth kinetics of the bacteria significantly. With parameter reestimation, the structure of our previously proposed PKPD model could well characterize the bacterial growth and killing kinetics when exposed to dynamic concentrations with different elimination rates of all five investigated antibiotics. Furthermore, the model with parameter estimates based on data from only the static time-kill curve experiments could predict the majority of the time-kill curves from the dynamic experiments reasonably well. Adding data from dynamic experiments in the estimation improved the model fit for cefuroxime and vancomycin, indicating some differences in sensitivity to experimental conditions among the antibiotics studied.
Activity of ACHN-490 Tested Alone and in Combination with Other Agents against Pseudomonas aeruginosa
Authors: Pankuch Glenn A. , Lin Gengrong , Kubo Aya , Armstrong Eliana S. , Appelbaum Peter C. , Kosowska-Shick Klaudia
Published: February 2011

ACHN-490 was tested alone and in combination with cefepime, doripenem, imipenem, or piperacillin-tazobactam in a synergy time-kill analysis against 25
Pseudomonas aeruginosa
strains with different resistance phenotypes. Each combination was synergistic against most isolates at 24 h, and antagonism was not observed. Combinations of ACHN-490 with cefepime, doripenem, imipenem, or piperacillin-tazobactam yielded synergies in ≥70% and ≥80% of strains at 6 and 12 h, respectively, and in ≥68% at 24 h.
Multilaboratory Testing of Two-Drug Combinations of Antifungals against
Candida albicans
,
Candida glabrata
, and
Candida parapsilosis
Authors: Chaturvedi Vishnu , Ramani Rama , Andes David , Diekema Daniel J. , Pfaller Michael A. , Ghannoum Mahmoud A. , Knapp Cindy , Lockhart Shawn R. , Ostrosky-Zeichner Luis , Walsh Thomas J. , Marchillo Karen , Messer Shawn , Welshenbaugh Amanda R. , Bastulli Cara , Iqbal Noreen , Paetznick Victor L. , Rodriguez Jose , Sein Tin
Published: February 2011

There are few multilaboratory studies of antifungal combination testing to suggest a format for use in clinical laboratories. In the present study, eight laboratories tested quality control (QC) strain
Candida parapsilosis
ATCC 22019 and clinical isolates
Candida albicans
20533.043,
C. albicans
20464.007,
Candida glabrata
20205.075, and
C. parapsilosis
20580.070. The clinical isolates had relatively high azole and echinocandin MICs. A modified CLSI M27-A3 protocol was used, with 96-well custom-made plates containing checkerboard pairwise combinations of amphotericin B (AMB), anidulafungin (AND), caspofungin (CSP), micafungin (MCF), posaconazole (PSC), and voriconazole (VRC). The endpoints were scored visually and on a spectrophotometer or enzyme-linked immunosorbent assay (ELISA) reader for 50% growth reduction (50% inhibitory concentration [IC
50
]). Combination IC
50
s were used to calculate summation fractional inhibitory concentration indices (FICIs) (ΣFIC) based on the Lowe additivity formula. The results revealed that the IC
50
s of all drug combinations were lower or equal to the IC
50
of individual drugs in the combination. A majority of the ΣFIC values were indifferent (ΣFIC = 0.51 to 2.0), but no antagonism was observed (ΣFIC ≥ 4). Synergistic combinations (ΣFIC ≤ 0.5) were found for AMB-PSC against
C. glabrata
and for AMB-AND and AMB-CSP against
C. parapsilosis
by both visual and spectrophotometric readings. Additional synergistic interactions were revealed by either of the two endpoints for AMB-AND, AMB-CSP, AMB-MCF, AMB-PSC, AMB-VRC, AND-PSC, CSP-MCF, and CSP-PSC. The percent agreements among participating laboratories ranged from 37.5% (lowest) for AND-CSP and POS-VOR to 87.5% (highest) for AMB-MCF and AND-CSP. Median ΣFIC values showed a wide dispersion, and interlaboratory agreements were less than 85% in most instances. Additional studies are needed to improve the interlaboratory reproducibility of antifungal combination testing.
Activity of the Fluoroquinolone DC-159a in the Initial and Continuation Phases of Treatment of Murine Tuberculosis
Authors: Ahmad Zahoor , Minkowski Austin , Peloquin Charles A. , Williams Kathy N. , Mdluli Khisimuzi E. , Grosset Jacques H. , Nuermberger Eric L.
Published: February 2011

DC-159a is a new fluoroquinolone with more potent
in vitro
activity than available fluoroquinolones against both drug-susceptible and fluoroquinolone-resistant
Mycobacterium tuberculosis
. Here, we report that DC-159a displays pharmacokinetics similar to those of moxifloxacin yet is more active than moxifloxacin during both the initial and continuation phases of treatment in a murine model. These results warrant further preclinical evaluation of DC-159a in selected drug combinations against drug-susceptible and fluoroquinolone-resistant tuberculosis.
Mupirocin Resistance in Staphylococcus aureus Causing Recurrent Skin and Soft Tissue Infections in Children
Authors: McNeil J. Chase , Hulten Kristina G. , Kaplan Sheldon L. , Mason Edward O.
Published: February 2011

Staphylococcus aureus
resistance to mupirocin is often caused by acquisition of a novel isoleucyl-tRNA synthetase encoded on the plasmid gene
mupA
. We tested
S. aureus
isolates from children at Texas Children's Hospital with recurrent skin and soft tissue infections for mupirocin resistance and
mupA
. Of 136 isolates, 20 were resistant to mupirocin (14.7%). Fifteen isolates (11%) carried
mupA
, and the gene was more common in methicillin-susceptible
S. aureus
(21.4%) than methicillin-resistant
S. aureus
(8.3%;
P
= 0.03). Seven of 20 mupirocin-resistant isolates displayed clindamycin resistance.
Effect of Antibiotic Treatment on the Intestinal Metabolome
Authors: Antunes L. Caetano M. , Han Jun , Ferreira Rosana B. R. , Lolić Petra , Borchers Christoph H. , Finlay B. Brett
Published: February 2011

The importance of the mammalian intestinal microbiota to human health has been intensely studied over the past few years. It is now clear that the interactions between human hosts and their associated microbial communities need to be characterized in molecular detail if we are to truly understand human physiology. Additionally, the study of such host-microbe interactions is likely to provide us with new strategies to manipulate these complex systems to maintain or restore homeostasis in order to prevent or cure pathological states. Here, we describe the use of high-throughput metabolomics to shed light on the interactions between the intestinal microbiota and the host. We show that antibiotic treatment disrupts intestinal homeostasis and has a profound impact on the intestinal metabolome, affecting the levels of over 87% of all metabolites detected. Many metabolic pathways that are critical for host physiology were affected, including bile acid, eicosanoid, and steroid hormone synthesis. Dissecting the molecular mechanisms involved in the impact of beneficial microbes on some of these pathways will be instrumental in understanding the interplay between the host and its complex resident microbiota and may aid in the design of new therapeutic strategies that target these interactions.
Frequency of Voriconazole Resistance
In Vitro
among Spanish Clinical Isolates of
Candida
spp. According to Breakpoints Established by the Antifungal Subcommittee of the European Committee on Antimicrobial Susceptibility Testing
Authors: Cuenca-Estrella M. , Gomez-Lopez A. , Cuesta I. , Zaragoza O. , Mellado E. , Rodriguez-Tudela J. L.
Published: February 2011

A total of 4,226 Spanish clinical isolates of
Candida
spp. were analyzed to assess resistance to voriconazole according to breakpoints established by the European Committee for Antimicrobial Susceptibility Testing (where susceptibility [S] to voriconazole corresponds to a MIC of ≤0.12 mg/liter). Resistance was uncommon among
Candida albicans
(5%),
C. parapsilosis
(1.2%), and
C. tropicalis
(11%) isolates. Voriconazole MICs of >0.12 mg/liter were more frequent among
Candida glabrata
and
C. krusei
isolates. A significant percentage of voriconazole-resistant strains came from oropharyngeal infections and exhibited high MICs of other azoles.
Regulatory Mechanism for Exfoliative Toxin Production in
Staphylococcus aureus
Authors: Kato Fuminori , Kadomoto Noriko , Iwamoto Yuko , Bunai Katsuaki , Komatsuzawa Hitoshi , Sugai Motoyuki
Published: February 2011

The exfoliative toxin (ET) is a major virulence factor of
Staphylococcus aureus
that causes bullous impetigo and its disseminated form, staphylococcal scalded-skin syndrome (SSSS). ET selectively digests one of the intracellular adhesion molecules, desmoglein 1, of epidermal keratinocytes and causes blisters due to intraepidermal cell-cell dissociation. Most
S. aureus
strains that cause blistering disease produce either ETA or ETB. They are serologically distinct molecules, where ETA is encoded on a phage genome and ETB is enocded on a large plasmid. ETA-producing
S. aureus
strains are frequently isolated from impetigo patients, and ETB-producing
S. aureus
strains are isolated from SSSS. ET-induced blister formation can be reproduced with the neonatal mouse. To determine the regulatory mechanism of ET production, we investigated the role of the two-component systems and global regulators for
eta
or
etb
expression
in vitro
and
in vivo
with the mouse model. Western blot and transcription analyses using a series of mutants demonstrate ETA production was downregulated by
sigB
,
sarS
, and
sarA
, while ETB production was downregulated by
sigB
and
sarA
but not by
sarS
. Production of both toxins is upregulated by
saeRS
,
arlRS
, and
agrCA
. Furthermore, by the
in vivo
neonatal mouse model,
sigB
and
sarS
but not
sarA
negatively regulate the exfoliation activity of the ETA-producing strain, while
sarA
negatively regulates the ETB-producing strain. In both strains,
saeRS
,
arlRS
, and
agrCA
positively regulate the exfoliation activity
in vivo
. The data illustrate similar but distinct regulatory mechanisms for ETA and ETB production
in S. aureus in vitro
as well as
in vivo
.
CD4+T Cells Are Not Essential for Control of Early AcuteCryptosporidium parvumInfection in Neonatal Mice
Authors: Korbel Daniel S. , Barakat Farah M. , Di Santo James P. , McDonald Vincent
Published: February 2011

Cryptosporidiosis is an important diarrheal disease of humans and neonatal livestock caused byCryptosporidiumspp. that infect epithelial cells. Recovery fromCryptosporidiumparvuminfection in adult hosts involves CD4+T cells with a strong Th1 component, but mechanisms of immunity in neonates are not well characterized. In the present investigation with newborn mice, similar acute patterns of infection were obtained in C57BL/6 wild-type (WT) and T and B cell-deficient Rag2−/−mice. In comparison with uninfected controls, the proportion of intestinal CD4+or CD8+T cells did not increase in infected WT mice during recovery from infection. Furthermore, infection in neonatal WT mice depleted of CD4+T cells was not exacerbated. Ten weeks after WT and Rag2−/−mice had been infected as neonates, no patent infections could be detected. Treatment at this stage with the immunosuppressive drug dexamethasone produced patent infections in Rag2−/−mice but not WT mice. Expression of inflammatory markers, including gamma interferon (IFN-γ) and interleukin-12p40 (IL-12p40), was higher in neonatal WT mice than in Rag2−/−mice around the peak of infection, but IL-10 expression was also higher in WT mice. These results suggest that although CD4+T cells may be important for elimination ofC. parvum, these cells are dispensable for controlling the early acute phase of infection in neonates.
Differential Requirements for NAIP5 in Activation of the NLRC4 Inflammasome
Authors: Lightfield Karla L. , Persson Jenny , Trinidad Norver J. , Brubaker Sky W. , Kofoed Eric M. , Sauer John-Demian , Dunipace Eric A. , Warren Sarah E. , Miao Edward A. , Vance Russell E.
Published: February 2011

Inflammasomes are cytosolic multiprotein complexes that assemble in response to infectious or noxious stimuli and activate the CASPASE-1 protease. The inflammasome containing the nucleotide binding domain-leucine-rich repeat (NBD-LRR) protein NLRC4 (interleukin-converting enzyme protease-activating factor [IPAF]) responds to the cytosolic presence of bacterial proteins such as flagellin or the inner rod component of bacterial type III secretion systems (e.g.,
Salmonella
PrgJ). In some instances, such as infection with
Legionella pneumophila
, the activation of the NLRC4 inflammasome requires the presence of a second NBD-LRR protein, NAIP5. NAIP5 also is required for NLRC4 activation by the minimal C-terminal flagellin peptide, which is sufficient to activate NLRC4. However, NLRC4 activation is not always dependent upon NAIP5. In this report, we define the molecular requirements for NAIP5 in the activation of the NLRC4 inflammasome. We demonstrate that the N terminus of flagellin can relieve the requirement for NAIP5 during the activation of the NLRC4 inflammasome. We also demonstrate that NLRC4 responds to the
Salmonella
protein PrgJ independently of NAIP5. Our results indicate that NAIP5 regulates the apparent specificity of the NLRC4 inflammasome for distinct bacterial ligands.
In Vivo
Leukocyte Changes Induced by
Escherichia coli
Subtilase Cytotoxin
Authors: Wang Hui , Paton Adrienne W. , McColl Shaun R. , Paton James C.
Published: February 2011

Subtilase cytotoxin (SubAB) is the prototype of a new family of AB
5
cytotoxins produced by Shiga-toxigenic
Escherichia coli
. Its cytotoxicity is due to its capacity to enter cells and specifically cleave the essential endoplasmic reticulum chaperone BiP. Previous studies have shown that intraperitoneal injection of mice with purified SubAB causes a pathology that overlaps with that seen in human cases of hemolytic-uremic syndrome, as well as dramatic splenic atrophy, suggesting that leukocytes are targeted. Here we investigated SubAB-induced leukocyte changes in the peritoneal cavity, blood, and spleen. After intraperitoneal injection, SubAB bound peritoneal leukocytes (including T and B lymphocytes, neutrophils, and macrophages). SubAB elicited marked leukocytosis, which peaked at 24 h, and increased neutrophil activation in the blood and peritoneal cavity. It also induced a marked redistribution of leukocytes among the three compartments: increases in leukocyte subpopulations in the blood and peritoneal cavity coincided with a significant decline in splenic cells. SubAB treatment also elicited significant increases in the apoptosis rates of CD4
+
T cells, B lymphocytes, and macrophages. These findings indicate that apart from direct cytotoxic effects, SubAB interacts with cellular components of both the innate and the adaptive arm of the immune system, with potential consequences for disease pathogenesis.
The OspE-Related Proteins Inhibit Complement Deposition and Enhance Serum Resistance of
Borrelia burgdorferi
, the Lyme Disease Spirochete
Authors: Kenedy Melisha R. , Akins Darrin R.
Published: February 2011

Borrelia burgdorferi
, the Lyme disease spirochete, binds the host complement inhibitors factor H (FH) and FH-like protein 1 (FHL-1). Binding of FH/FHL-1 by the
B. burgdorferi
proteins CspA and the OspE-related proteins is thought to enhance resistance to serum-mediated killing. While previous reports have shown that CspA confers serum resistance in
B. burgdorferi
, it is unclear whether the OspE-related proteins are relevant in
B. burgdorferi
serum resistance when OspE is expressed on the borrelial surface. To assess the role of the OspE-related proteins, we overexpressed them in a serum-sensitive CspA mutant strain. OspE overexpression enhanced serum resistance of the CspA-deficient organisms. Furthermore, FH was more efficiently bound to the
B. burgdorferi
surface when OspE was overexpressed. Deposition of complement components C3 and C5b-9 (the membrane attack complex), however, was reduced on the surface of the OspE-overexpressing strain compared to that on the CspA mutant strain. These data demonstrate that OspE proteins expressed on the surface of
B. burgdorferi
bind FH and protect the organism from complement deposition and subsequent serum-mediated destruction.
Murine Immune Response to a Chronic
Staphylococcus aureus
Biofilm Infection
Authors: Prabhakara Ranjani , Harro Janette M. , Leid Jeff G. , Harris Megan , Shirtliff Mark E.
Published: February 2011

Staphylococcus aureus
has reemerged as an important human pathogen in recent decades. Although many infections caused by this microbial species persist through a biofilm mode of growth, little is known about how the host's adaptive immune system responds to these biofilm infections. In this study,
S. aureus
cells adhered to pins in culture and were subsequently inserted into the tibiae of C57BL/6 mice, with an infecting dose of 2 × 10
5
CFU. This model was utilized to determine local cytokine levels, antibody (Ab) function, and T cell populations at multiple time points throughout infection. Like human hosts,
S. aureus
implant infection was chronic and remained localized in 100% of C57BL/6 mice at a consistent level of approximately 10
7
CFU/gram bone tissue after day 7. This infection persisted locally for >49 days and was recalcitrant to clearance by the host immune response and antimicrobial therapy. Local inflammatory cytokines of the Th1 (interleukin-2 [IL-2], IL-12 p70, tumor necrosis factor alpha [TNF-α], and IL-1β) and Th17 (IL-6 and IL-17) responses were upregulated throughout the infection, except IL-12 p70, which dwindled late in the infection. In addition, Th1 Ab subtypes against a biofilm antigen (SA0486) were upregulated early in the infection, while Th2 Abs and anti-inflammatory regulatory T cells (Tregs) were not upregulated until later. These results indicate that early Th1 and Th17 inflammatory responses and downregulated Th2 and Treg responses occur during the development of a chronic biofilm implant infection. This unrestrained inflammatory response may cause tissue damage, thereby enabling
S. aureus
to attach and thrive in a biofilm mode of growth.
Physicians promoting physical activity using pedometers and community partnerships: a real world trial
Authors: Trinh Linda , Wilson Ron , Williams Heather MacLeod , Sum Alison J , Naylor Patti-Jean
Published: February 2011

Background

Healthcare providers are a primary source of information on preventive health issues for patients. Further research related to physical activity (PA) promotion in the primary care setting is needed.

Objective

To explore the feasibility of a physician and community PA intervention using a pedometer for: increasing PA levels among inactive patients; enhancing relationships between physicians and community PA partners; and influencing the PA promotion habits of physicians.

Methods

A 6-week PA intervention was delivered to 152 inactive patients who were recruited in physician waiting rooms, counselled by their physicians, provided with a pedometer and referred to a community action site (CAS) at their local recreation centre for further support. PA was measured at baseline and follow-up using the International Physical Activity Questionnaire. Follow-up interviews were conducted with physicians and recreation representatives on the challenges and benefits associated with the intervention.

Results

Study patients significantly increased their PA (103% change in MET min/week). Physicians and recreation professionals were highly satisfied with the intervention and partnership. There were challenges to ongoing communication. Physicians reported increased awareness of the pedometer and community resources as supports for PA.

Conclusion

A pedometer-based PA intervention delivered by physicians in partnership with a community PA stakeholder is feasible and warrants further research. Long-term maintenance of this intervention would require resources for pedometers, and ongoing contact and communication between the physicians and CAS to ensure availability of community supports.
Long-term safety and effectiveness of inferior vena cava filters in patients with stroke
Authors: Somarouthu Bhanusupriya , Yeddula Kalpana , Wicky Stephan , Hirsch Joshua A , Kalva Sanjeeva P
Published: February 2011

Purpose

To assess the long-term safety and clinical effectiveness of inferior vena cava (IVC) filters in patients with stroke.

Method and materials

In this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant retrospective study, we reviewed the clinical data of patients who had stroke and were treated with an IVC filter from 2002 to 2009. The demographics, clinical data, indications for IVC filter, procedural complications, symptomatic post-filter pulmonary embolism (PE) and deep vein thrombosis (DVT), caval occlusion and incidental, imaging-evident filter-related complications were recorded. Safety was assessed through occurrence of filter-related complications during placement and follow-up. Effectiveness was assessed through occurrence of post-filter fatal and non-fatal PE.

Results

During this period, 371 patients (224 male; mean age 67.5 years) with stroke received an IVC filter. The stroke was hemorrhagic in 28%, ischemic in 20%, associated with intracranial malignancy in 21% and trauma in 31%. 235 (63%) patients (PE in 159) had venous thromboembolism on imaging. The indications for IVC filter included contraindication to anticoagulation in 251 (68%), prophylaxis in 83 (22%), added protection in 22 (6%) and complication or failure of anticoagulation in 15 (4%). There was one procedural complication. During a follow-up of 1.74±2.36 years, 180 (49%) patients died, three due to post-filter PE and the remainder all due to primary disease. Symptomatic post-filter PE and DVT occurred at a frequency of 15% (54/371) and 16% (60/371), respectively. Of these, 15 (4%) had imaging-proven PE. Three (0.8%) succumbed to post-filter PE. Imaging-proven new or recurrent DVT occurred in 6% and 8%, respectively. Symptomatic caval occlusion was seen in five (5/371, 1.3%).

Conclusion

IVC filters have an acceptable safety profile in stroke patients. In our cohort, they were effective in preventing life-threatening PE.
Transnational tobacco industry promotion of the cigarette gifting custom in China
Authors: Chu Alexandria , Jiang Nan , Glantz Stanton A
Published: February 2011

Objective

To understand how British American Tobacco (BAT) and Philip Morris (PM) researched the role and popularity of cigarette gifting in forming relationships among Chinese customs and how they exploited the practice to promote their brands State Express 555 and Marlboro.

Methods

Searches and analysis of industry documents from the Legacy Tobacco Documents Library complemented by searches on LexisNexis Academic news, online search engines and information from the tobacco industry trade press.

Results

From 1980–1999, BAT and PM employed Chinese market research firms to gather consumer information about perceptions of foreign cigarettes and the companies discovered that cigarettes, especially prestigious ones, were gifted and smoked purposely for building relationships and social status in China. BAT and PM promoted their brands as gifts by enhancing cigarette cartons and promoting culturally themed packages, particularly during the gifting festivals of Chinese New Year and Mid-Autumn Festival to tie their brands in to festival values such as warmth, friendship and celebration. They used similar marketing in Chinese communities outside China.

Conclusions

BAT and PM tied their brands to Chinese cigarette gifting customs by appealing to social and cultural values of respect and personal honour. Decoupling cigarettes from their social significance in China and removing their appeal would probably reduce cigarette gifting and promote a decline in smoking. Tobacco control efforts in countermarketing, large graphic warnings and plain packaging to make cigarette packages less attractive as gifts could contribute to denormalising cigarette gifting.
REEMERGENCE OF THE COLLECTIVE MODE IN 3HE AND ELECTRON LAYERS
Authors: BÖHM HELGA M. , HOLLER ROBERT , KROTSCHECK ECKHARD , PANHOLZER MARTIN , GODFRIN HENRY , MESCHKE MATHIAS , LAUTER HANS-JOCHEN
Published: February 2011

Neutron scattering experiments on a 3 He layer on graphite show an unexpected behavior of the collective mode. After having been broadened by Landau damping at intermediate wave vectors, the phonon-roton mode resharpens at large wave vectors and even emerges from the particle-hole continuum at low energies. The measured spectra cannot be explained by a random phase approximation with any static interaction. We show here that the data are well described if dynamic two-pair fluctuations are accounted for. We predict similar effects for electron layers.
DISSECTING AND TESTING COLLECTIVE AND TOPOLOGICAL SCENARIOS FOR THE QUANTUM CRITICAL POINT
Authors: CLARK J. W. , KHODEL V. A. , ZVEREV M. V.
Published: February 2011

In a number of strongly-interacting Fermi systems, the existence of a quantum critical point (QCP) is signaled by a divergent density of states and effective mass at zero temperature. Competing scenarios and corresponding mechanisms for the QCP are contrasted and analyzed. The conventional scenario invokes critical fluctuations of a collective mode in the close vicinity of a second-order phase transition and attributes divergence of the effective mass to a coincident vanishing of the quasiparticle pole strength. It is argued that this collective scenario is disfavored by certain experimental observations as well as theoretical inconsistencies, including violation of conservation laws applicable in the strongly interacting medium. An alternative topological scenario for the QCP is developed self-consistently within the general framework of Landau quasiparticle theory. In this scenario, the topology of the Fermi surface is transfigured when the quasiparticle group velocity vanishes at the QCP, yet the quasiparticle picture remains meaningful and no symmetry is broken. The topological scenario is found to explain the non-Fermi-liquid behavior observed experimentally in Yb-based heavy-fermion systems close to the QCP. This study suggests that integration of the topological scenario with the theory of second-order, symmetry-breaking quantum phase transitions will furnish a proper foundation for theoretical understanding of the extended QCP region.
DISSIPATIVE PROCESSES IN LOW DENSITY STRONGLY INTERACTING 2D ELECTRON SYSTEMS
Authors: NEILSON DAVID
Published: February 2011

A glassy phase in disordered two dimensional (2D) electron systems may exist at low temperatures for electron densities lying intermediate between the Fermi liquid and Wigner crystal limits. The glassy phase is generated by the combined effects of disorder and the strong electron-electron correlations arising from the repulsive Coulomb interactions. Our approach here is motivated by the observation that at low electron densities the electron pair correlation function, as numerically determined for a non-disordered 2D system from Monte Carlo simulations, is very similar to the pair correlation function for a 2D classical system of hard discs. This suggests that theoretical approaches to 2D classical systems of hard discs may be of use in studying the disordered, low density electron problem. We use this picture to study its dynamics on the electron-liquid side of a glass transition. At long times the major relaxation process in the electron-liquid will be a rearrangement of increasingly large groups of the discs, rather than the movement of the discs separately. Such systems have been studied numerically and they display all the characteristics of glassy behaviour. There is a slowing down of the dynamics and a limiting value of the retarded spatial correlations. Motivated by the success of mode-coupling theories for hard spheres and discs in reproducing experimental results in classical fluids, we use the Mori formalism within a mode-coupling theory to obtain semi-quantitative insight into the role of electron correlations as they affect the time response of the weakly disordered 2D electron system at low densities.
RENORMALIZED BOSONS AND FERMIONS
Authors: GERNOTH K. A. , RISTIG M. L.
Published: February 2011

Correlated Density Matrix (CDM) theory permits formal analyses of microscopic properties of strongly correlated quantum fluids and liquids at nonzero temperatures. Equilibrium properties, thermodynamic potentials, correlation and structure functions can be studied formally as well as numerically within the CDM algorithm. Here we provide the essential building blocks for studying the radial distribution function and the single-particle momentum distribution of the ingredients of the quantum systems. We focus on the statistical properties of correlated fluids and introduce the concept of renormalized bosons and fermions. These entities carry the main statistical features of the correlated systems such as liquid 4 He through their specific dependence on temperature, particle number density, and wavenumber encapsulated in their effective masses. The formalism is developed for systems of bosons and of fermions. Numerical calculations for fluid 4 He in the normal phase demonstrate the power of the renormalization concept. The formalism is further extended to analyze the Bose-Einstein condensed phases and gives a microscopic understanding of Tisza's two-fluid model for the normal and superfluid density components.
THERMODYNAMIC DETECTION OF QUANTUM PHASE TRANSITIONS
Authors: KRUSE M. K. G. , MILLER H. G. , PLASTINO A. , PLASTINO A. R.
Published: February 2011

We show that, by recourse to thermodynamics's third law, quantum phase transitions in a system of fermions can be detected, in the sense that thereby one automatically finds the values of the external parameter (here coupling strengths of the pertinent Hamiltonian) at which these transitions occur. We illustrate our considerations with reference to an exactly solvable model of Plastino and Moszkowski [Il Nuovo Cimento 47, 470 (1978)].
QUASI-ONE DIMENSIONAL FLUIDS THAT EXHIBIT HIGHER DIMENSIONAL BEHAVIOR
Authors: GATICA SILVINA M. , CALBI M. MERCEDES , STAN GEORGE , TRASCA R. ANDREEA , COLE MILTON W.
Published: February 2011

Fluids confined within narrow channels exhibit a variety of phases and phase transitions associated with their reduced dimensionality. In this review paper, we illustrate the crossover from quasi-one dimensional to higher effective dimensionality behavior of fluids adsorbed within different carbon nanotubes geometries. In the single nanotube geometry, no phase transitions can occur at finite temperature. Instead, we identify a crossover from a quasi-one dimensional to a two dimensional behavior of the adsorbate. In bundles of nanotubes, phase transitions at finite temperature arise from the transverse coupling of interactions between channels.
QUANTUM PROPERTIES IN TRANSPORT THROUGH NANOSCOPIC RINGS: CHARGE-SPIN SEPARATION AND INTERFERENCE EFFECTS
Authors: HALLBERG K. , RINCON JULIAN , RAMASESHA S.
Published: February 2011

Many of the most intriguing quantum effects are observed or could be measured in transport experiments through nanoscopic systems such as quantum dots, wires and rings formed by large molecules or arrays of quantum dots. In particular, the separation of charge and spin degrees of freedom and interference effects have important consequences in the conductivity through these systems.

Charge-spin separation was predicted theoretically in one-dimensional strongly interacting systems (Luttinger liquids) and, although observed indirectly in several materials formed by chains of correlated electrons, it still lacks direct observation. We present results on transport properties through Aharonov-Bohm rings (pierced by a magnetic flux) with one or more channels represented by paradigmatic strongly-correlated models. For a wide range of parameters we observe characteristic dips in the conductance as a function of magnetic flux which are a signature of spin and charge separation.

Interference effects could also be controlled in certain molecules and interesting properties could be observed. We analyze transport properties of conjugated molecules, benzene in particular, and find that the conductance depends on the lead configuration. In molecules with translational symmetry, the conductance can be controlled by breaking or restoring this symmetry, e.g. by the application of a local external potential.

These results open the possibility of observing these peculiar physical properties in anisotropic ladder systems and in real nanoscopic and molecular devices.
COOPERATIVE LOCALIZATION-DELOCALIZATION IN THE HIGH Tc CUPRATES
Authors: RANNINGER JULIUS
Published: February 2011

The intrinsic metastable crystal structure of the cuprates results in local dynamical lattice instabilities, strongly coupled to the density fluctuations of the charge carriers. They acquire in this way simultaneously both, delocalized and localized features. It is responsible for a partial fractioning of the Fermi surface, i.e., the Fermi surface gets hidden in a region around the anti-nodal points, because of the opening of a pseudogap in the normal state, arising from a partial charge localization. The high energy localized single-particle features are a result of a segregation of the homogeneous crystal structure into checker-board local nano-size structures, which breaks the local translational and rotational symmetry. The pairing in such a system is dynamical rather than static, whereby charge carriers get momentarily trapped into pairs in a deformable dynamically fluctuating ligand environment. We conclude that the intrinsically heterogeneous structure of the cuprates must play an important role in this type of superconductivity.
THERMODYNAMICALLY STABLE VORTEX STATES IN SUPERCONDUCTING NANOWIRES
Authors: WU W. M. , SOBNACK M. B. , KUSMARTSEV F. V.
Published: February 2011

We develop a new condensed matter theory of the formation of thermodynamically stable vortex structures in quantum nanowires. We write down the Gibbs free energy functional for the systems and we minimise the free energy to obtain the optimal position of vortices for different applied fields and temperatures. We also study the nucleation of vortices in, and their escape from, the nanostructural superconductors.
QUANTUM INFORMATION IN OPTICAL LATTICES
Authors: GUZMÁN ANGELA M. , DUEÑAS E. MARCO A.
Published: February 2011

Experimental realizations of a two-qubit quantum logic gate based on cold atom collisions have been elusive mainly due to the decoherence effects introduced during the quantum gate operation, which cause transitions out of the two-qubit space and lead to a decreased gate operation fidelity. This type of decoherence effects, due to the non closeness of the interacting two-qubit system, are characteristic of the electromagnetic interaction, since the electromagnetic vacuum acts as a reservoir whose eigenmodes might become active during the gate operation. To describe the cold-atom collision we consider the quantum non-Hermitian dipole-dipole interaction instead of the less realistic s-scattering approach widely used in the literature. By adding an ancillary qubit, we take advantage of the spatial modulation of the non-Hermitian part of the interaction potential to obtain a "resonant" condition that should be satisfied to achieve lossless operation of a specific two-qubit quantum phase-gate. We demonstrate that careful engineering of the collision is required to obtain a specific truth table and to suppress the effects inherent in the openness of the system arising from the electromagnetic interaction.
NUMERICAL ANALYSIS OF HYDROGEN STORAGE IN CARBON NANOPORES
Authors: WEXLER CARLOS , OLSEN RAINA , PFEIFER PETER , KUCTHA BOGDAN , FIRLEJ LUCYNA , ROSZAK SZTEPAN
Published: February 2011

Carbon-based materials, due to their low cost and weight, have long been considered as suitable physisorption substrates for the reversible storage of hydrogen. Nanoporous carbons can be engineered to achieve exceptional storage capacities: gravimetric excess adsorption of 0.073 ± 0.003 kg H 2/ kg carbon, gravimetric storage capacity of 0.106 ± 0.005 kg H 2/ kg carbon, and volumetric storage capacity of 0.040 ± 0.002 kg H 2/liter carbon, at 80 K and 50 bar. The nanopores generage high storage capacity by having a very high surface are, by generating a high H 2-wall interaction potential, and by allowing multi-layer adsorption of H 2 (at cryogenic temperatures). In this paper we show how the experimental adsorption isotherms can be understood from basic theoretical considerations and computational simulations of the adsorption in a bimodal distribution of narrow and wide pore spaces. We also analyze the possibility of multi-layer adsorption, and the effects of hypothetical larger adsorption energies. Finally, we present the results of coupled ab initio calculations and Monte Carlo simulations showing that partial substitution of carbon atoms in nanoporous matrix with boron results in significant increases of the adsorption energy and storage capacity.
GENERALIZED SUPERCONDUCTING GAP IN A BOSON-FERMION MODEL
Authors: MAMEDOV T. A. , DE LLANO M.
Published: February 2011

A quantum-statistical binary gas mixture model consisting of positive-energy resonant bosonic Cooper electron pairs in chemical and thermal equilibrium with single unpaired electrons yields, via two-time retarded Green functions, an analytic expression for a dimensionless coupling λ- and temperature T-dependent generalized energy gap Eg(λ, T) in the single-electron spectrum. The new gap gives a reasonable description of overdoped Bi2Sr2CuO6+δ(Bi2201).
BOLTZMANN'S ERGODIC HYPOTHESIS: A MEETING PLACE FOR TWO CULTURES
Authors: LEE M. HOWARD
Published: February 2011

The physical theory for the ergodic hypothesis is premised on the idea that the hypothesis is measurable by scattering experiment. Therewith it proves the hypothesis by measurable properties of the response function. Birkhoff's theorem proves the ergodic hypothesis by abstract properties of phase space, the measure and transitivity. In this work we apply the two independent approaches to a particular many-body model (spin-1/2 XY model) to see whether they arrive at the same conclusions on the ergodicity question. The two approaches are compared to gain insight into their goals.
ELECTRON-ELECTRON INTERACTION IN THE NON-RELATIVISTIC LIMIT
Authors: MALIK F. BARY
Published: February 2011

The electron-electron potential in the one-photon exchange approximation with the omission of the spin-spin interaction, leads to the classical Coulomb interaction, but the inclusion of the latter results in the Møller interaction. Bethe and Fermi showed that the latter interaction leads to the Breit potential, if a few of the terms in the expansion of the retardation effect are considered. In this article, it is shown that the higher order terms omitted in the Bethe-Fermi treatment reduces to terms of the same order in Dirac's alpha-matrices considered by Bethe and Fermi. This raises questions whether the Breit interaction is the appropriate first order correction to the Coulomb potential in the non-relativistic limit. It is pointed out that the nature of the interaction between two bound (1s) electron derived by Brown using the Schwinger formalism of the quantum electrodynamics but proposed empirically in 1929 by Gaunt could be a better correction to the Coulomb potential for bound electrons in atoms. The calculated energies using these matrix elements plus the vacuum polarization energies are in reasonable agreement with the data. For comparison, calculated energies using the Breit interaction plus vacuum polarization energies are also presented.
ON FLOW BARRIERS AND SWITCHABILITY IN DISCONTINUOUS DYNAMICAL SYSTEMS
Authors: LUO ALBERT C. J.
Published: February 2011

In this paper, the theory of flow barriers in discontinuous dynamical systems is systematically presented as a new theory for the first time, which helps one rethink the existing theories of stability and control in dynamical systems. The concept of flow barriers in discontinuous dynamical systems is introduced, and the passability of a flow to the separation boundary with flow barriers is presented. Because the flow barriers exist on the separation boundary, the switchability of a flow to such a separation boundary is changed accordingly. The coming and leaving flow barriers in passable flows are discussed first, and the necessary and sufficient conditions for a flow to pass through the boundary with flow barrier are developed. Flow barriers for sink and source flows are also discussed. Once the sink flow is formed, the boundary flow will exist. When the boundary flow disappears from the boundary, the boundary flow barrier on the boundary may exist, which is independent of vector fields in the corresponding domains. Thus, the necessary and sufficient conditions for formations and vanishing of the boundary flow are developed. A periodically forced friction model is presented as an example for a better understanding of flow barrier existence in physical problems. The flow barrier theory presented in this paper may provide a theoretic base to further develop control theory and stability.
NONRESONANT BIFURCATIONS OF HETEROCLINIC LOOPS WITH ONE INCLINATION FLIP
Authors: SHUI SHULIANG , LI JINGJING , ZHANG XUYANG
Published: February 2011

Heteroclinic bifurcations in four-dimensional vector fields are investigated by setting up local coordinates near a heteroclinic loop. This heteroclinic loop consists of two principal heteroclinic orbits, but there is one stable foliation that involves an inclination flip. The existence, nonexistence, coexistence and uniqueness of the 1-heteroclinic loop, 1-homoclinic orbit, and 1-periodic orbit are studied. Also, the nonexistence, existence of the 2-homoclinic and 2-periodic orbit are demonstrated.
VIBRATIONAL RESONANCE IN AN ASYMMETRIC DUFFING OSCILLATOR
Authors: JEYAKUMARI S. , CHINNATHAMBI V. , RAJASEKAR S. , SANJUAN M. A. F.
Published: February 2011

We analyze how the asymmetry of the potential well of the Duffing oscillator affects the vibrational resonance. We obtain, numerically and theoretically, the values of the low-frequency and amplitude of the high-frequency forces at which vibrational resonance occurs. Furthermore, we observe that an additional resonance is induced by the asymmetry of the potential well. We account the additional resonance in terms of resonant frequency of the slow motion of the system. Resonance occurs in the asymmetric system for the input signal frequency range for which it is not possible in the symmetric system. Resonance is also studied with nonsinusoidal input signals and in the presence of additive Gaussian white noise.
DYNAMIC KNOWLEDGE EXTRACTION FROM SOFTWARE SYSTEMS USING SEQUENTIAL PATTERN MINING
Authors: SARTIPI KAMRAN , SAFYALLAH HOSSEIN
Published: February 2011

Software system analysis for identifying software functionality in source code remains a major problem in the reverse engineering literature. The early approaches for extracting software functionality mainly relied on static properties of software system. However, the static approaches by nature suffer from the lack of semantic and hence are not appropriate for this task. This paper presents a novel technique for dynamic analysis of software systems to identify the implementation of certain software functionality known as software features. In the proposed approach, a specific feature is shared by a number of task scenarios that are applied on the software system to generate execution traces. The application of a sequential pattern mining technique on the generated execution traces allows us to extract execution patterns that reveal the specific feature functionality. In a further step, the extracted execution patterns are distributed over a concept lattice to separate feature-specific group of functions from commonly used group of functions. The use of lattice also allows for identifying a family of closely related features in the source code. Moreover, in this work we provide a set of metrics for evaluating the structural merits of the software system such as component cohesion and functional scattering. We have implemented a prototype toolkit and experimented with two case studies Xfig drawing tool and Pine email client with very promising results.
STABILITY OF ACOUSTIC PROPAGATION IN 2D DUCT FLOWS: A LOW FREQUENCY APPROACH
Authors: BONNET-BEN DHIA A.-S. , DURUFLE M. , JOLY P. , JOUBERT L.
Published: February 2011

In this paper, we derive a simplified "quasi-1D" limit model for the propagation of low frequency acoustic waves in a laminar flow filling a 2D duct. We analyze the well-posedness of this model in function of the Mach profile of the flow. This can be reduced to the study of the spectrum of a bounded non-normal operator. As a by-product of this analysis, we establish new results for hydrodynamic instabilities of Kelvin–Helmholtz type in compressible fluids.
GRAVITATIONAL THERMODYNAMICS AND THE WHEELER–DEWITT EQUATION
Authors: POLLOCK M. D.
Published: February 2011

In a previous paper, we have derived the Hawking temperature T H = 1/8πM for a Schwarzschild black hole of mass M, starting from the Wheeler–DeWitt for the wave function Ψ on the apparent horizon, due to Tomimatsu. Here we discuss the derivation of this result in greater detail, with particular regard to the Euclideanization procedure involved and the boundary conditions on the horizon. Further, analysis of the de Sitter space-time generated by a cosmological constant Λ yields the temperature [Formula: see text] found by Gibbons and Hawking, which thus vindicates the method. The emission of radiation occurs with preservation of unitarity, and hence entropy, which is substantiated by a global thermodynamical argument in the case of the black hole.
HIGHER-ORDER CURVATURE TERMS IN BORN–INFELD TYPE BRANE THEORIES
Authors: ROJAS EFRAIN
Published: February 2011

The field equations associated to Born–Infeld type brane theories are studied by using auxiliary variables. This approach hinges on the fact, that the expressions defining the physical and geometrical quantities describing the worldvolume are varied independently. The general structure of the Born–Infeld type theories for branes contains the square root of a determinant of a combined matrix between the induced metric on the worldvolume swept out by the brane and a symmetric/antisymmetric tensor depending on gauge, matter or extrinsic curvature terms taking place on the worldvolume. The higher-order curvature terms appearing in the determinant form come to play in competition with other effective brane models. Additionally, we suggest a Born–Infeld–Einstein type action for branes where the higher-order curvature content is provided by the worldvolume Ricci tensor. This action provides an alternative description of the dynamics of braneworld scenarios.