bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytolethal Distending Toxin Type I and Type IV Genes Are Framed with Lambdoid Prophage Genes in Extraintestinal Pathogenic
Escherichia coli
Authors: Tóth István , Nougayrède Jean-Philippe , Dobrindt Ulrich , Ledger Terence Neil , Boury Michèle , Morabito Stefano , Fujiwara Tamaki , Sugai Motoyuki , Hacker Jörg , Oswald Eric
Published: November 2008

Five types of cytolethal distending toxin (CDT-I to CDT-V) have been identified in
Escherichia coli
. In the present study we cloned and sequenced the
cdt-IV
operon and flanking region from a porcine extraintestinal pathogenic
E. coli
(ExPEC) strain belonging to serogroup O75. We confirmed that similar to other CDTs, CDT-IV induced phosphorylation of host histone H2AX, a sensitive marker of DNA double-strand breaks, and blocked the HeLa cell cycle at the G
2
-M transition. The
cdt-IV
genes were framed by lambdoid prophage genes. We cloned and sequenced the
cdt-I
operon and flanking regions from a human ExPEC O18:K1:H7 strain and observed that
cdt-I
genes were also flanked by lambdoid prophage genes. PCR studies indicated that a gene coding for a putative protease was always associated with the
cdtC-IV
gene but was not associated with
cdtC
genes in strains producing CDT-I, CDT-III, and CDT-V. Our results suggest that the
cdt-I
and
cdt-IV
genes might have been acquired from a common ancestor by phage transduction and evolved in their bacterial hosts. The lysogenic bacteriophages have the potential to carry nonessential “cargo” genes or “morons” and therefore play a crucial role in the generation of genetic diversity within ExPEC.
A RecB-Like Helicase in
Helicobacter pylori
Is Important for DNA Repair and Host Colonization
Authors: Wang Ge , Maier Robert J.
Published: November 2008

The human gastric pathogen
Helicobacter pylori
encounters frequent oxidative and acid stress in its specific niche, and this causes bacterial DNA damage.
H. pylori
exhibits a very high degree of DNA recombination, which is required for repairing both DNA double-stranded (ds) breaks and blocked replication forks. Nevertheless, few genes encoding components of DNA recombinational repair processes have been identified in
H. pylori
. An
H. pylori
mutant defective in a putative helicase gene (HP1553) was constructed and characterized herein. The HP1553 mutant strain was much more sensitive to mitomycin C than the WT strain, indicating that HP1553 is required for repair of DNA ds breaks. Disruption of HP1553 resulted in a significant decrease in the DNA recombination frequency, suggesting that HP1553 is involved in DNA recombination processes, probably functioning as a RecB-like helicase. HP1553 was shown to be important for
H. pylori
protection against oxidative stress-induced DNA damage, as the exposure of the HP1553 mutant cells to air for 6 h caused significant fragmentation of genomic DNA and led to cell death. In a mouse infection model, the HP1553 mutant strain displayed a greatly reduced ability to colonize the host stomachs, indicating that HP1553 plays a significant role in
H. pylori
survival/colonization in the host.
Sustained Activation of Akt and Erk1/2 Is Required forCoxiella burnetiiAntiapoptotic Activity
Authors: Voth Daniel E. , Heinzen Robert A.
Published: November 2008

Coxiella burnetiiis an obligate intracellular bacterial pathogen that directs biogenesis of a lysosome-like, parasitophorous vacuole in mammalian cells. We recently reported thatC. burnetiiinhibits apoptotic cell death in macrophages, presumably as a mechanism to sustain the host for completion of its lengthy infectious cycle. In the current study, we further investigatedC. burnetiimanipulation of host cell signaling and apoptosis by examining the effect ofC. burnetiiinfection on activation of 15 host proteins involved in stress responses, cytokine production, and apoptosis.C. burnetiiinfection of THP-1 human macrophage-like cells caused increased levels of phosphorylated c-Jun, Hsp27, Jun N-terminal protein kinase, and p38 at 2 h postinfection (hpi), and this activation rapidly decreased to near basal levels by 24 hpi. The prosurvival kinases Akt and Erk1/2 (extracellular signal-regulated kinases 1 and 2) were also activated at 2 to 6 hpi; however, the phosphorylation of these proteins increased coincident withC. burnetiireplication through at least 72 hpi. Sustained phosphorylation of Akt and Erk1/2 was abolished by treatment of infected cells with rifampin, indicating their activation is aC. burnetii-directed event requiring pathogen RNA synthesis. Moreover, pharmacological inhibition of Akt or Erk1/2 significantly decreasedC. burnetiiantiapoptotic activity. Collectively, these results indicate the importance ofC. burnetiimodulation of host signaling and demonstrate a critical role for Akt and Erk1/2 in successful intracellular parasitism and maintenance of host cell viability.
Function, Regulation, and Transcriptional Organization of the Hemin Utilization Locus of
Bartonella quintana
Authors: Parrow Nermi L. , Abbott Jasmin , Lockwood Amanda R. , Battisti James M. , Minnick Michael F.
Published: November 2008

Bartonella quintana
is a gram-negative agent of trench fever, chronic bacteremia, endocarditis, and bacillary angiomatosis in humans.
B. quintana
has the highest known hemin requirement among bacteria, but the mechanisms of hemin acquisition are poorly defined. Genomic analyses revealed a potential locus dedicated to
h
emin
ut
ilization (
hut
) encoding a putative hemin receptor, HutA; a TonB-like energy transducer; an ABC transport system comprised of three proteins, HutB, HutC, and HmuV; and a hemin degradation/storage enzyme, HemS. Complementation analyses with
Escherichia coli hemA
show that HutA functions as a hemin receptor, and complementation analyses with
E. coli hemA tonB
indicate that HutA is TonB dependent. Quantitative reverse transcriptase PCR analyses show that
hut
locus transcription is subject to hemin-responsive regulation, which is mediated primarily by the iron response regulator (Irr). Irr functions as a transcriptional repressor of the
hut
locus at all hemin concentrations tested. Overexpression of the ferric uptake regulator (
fur
) represses transcription of
tonB
in the presence of excess hemin, whereas overexpression of the rhizobial iron regulator (
rirA
) has no effect on
hut
locus transcription. Reverse transcriptase PCR analyses show that
hutA
and
tonB
are divergently transcribed and that the remaining
hut
genes are expressed as a polycistronic mRNA. Examination of the promoter regions of
hutA
,
tonB
, and
hemS
reveals consensus sequence promoters that encompass an H-box element previously shown to interact with
B. quintana
Irr.
The effects of inhaled L-methamphetamine on athletic performance while riding a stationary bike: a randomised placebo-controlled trial
Authors: Dufka F , Galloway G , Baggott M , Mendelson J
Published: November 2008

Objective:

L-methamphetamine (the non-abused isomer of methamphetamine) is banned in athletic competition because it may improve athletic performance, but there are no studies assessing its effects on performance. In the United States L-methamphetamine is formulated in the non-prescription Vick’s Vapor Inhaler (VVI) nasal decongestant. VVIs sold elsewhere (we used ones from the UK) contain similar inactive ingredients (menthol, camphor and Siberian pine oil) but no L-methamphetamine. This study tested the effects of inhaled L-methamphetamine delivered from a widely available non-prescription product on athletic performance.

Design:

In a 2-session double-blind placebo-controlled study 12 participants (ages 14–17) were dosed with 4 (session 1) and 12 (session 2) inhalations from VVIs with (USA) or without (UK) L-methamphetamine and then performed two 20 minute rides on a stationary bike with rides separated by a 30 minute rest.

Outcome measure:

The main outcome measure was miles travelled during each 20 minute ride. Secondary outcome measures included postride urine toxicology; heart rate and blood pressure before, 1, 5 and 10 minutes postride; energy, performance, endurance, and ability to breathe; and VVI preference. Data were analysed using Excel statistical macros.

Results:

After ∼16 μg L-methamphetamine distance travelled was 5.26 (SD 0.53) miles vs 5.30 (0.55) with placebo; p = 0.81. After ∼48 μg L-methamphetamine distance travelled was 5.30 (0.51) vs 5.35 (0.43) with placebo; p = 0.85. The ∼16 μg dose increased systolic blood pressure from 72.6 (4.3) to 79.6 (6.6) mm Hg (p = 0.03) at 5 minutes postride but there were no other differences in outcomes.

Conclusions:

Modest doses of inhaled L-methamphetamine probably do not improve athletic performance but do minimally raise diastolic blood pressure.
Cause of Exercise Associated Muscle Cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion?
Authors: Schwellnus M P
Published: November 2008

Exercise Associated Muscle Cramps (EAMC) is one of the most common conditions that require medical attention during or immediately after sports events. Despite the high prevalence of this condition the aetiology of EAMC in athletes is still not well understood. The purpose of this review is to examine current scientific evidence in support of (1) the “electrolyte depletion” and “dehydration” hypotheses and (2) the “altered neuromuscular control” hypothesis in the aetiology of EAMC. In this review, scientific evidence will, as far as possible, be presented using evidence-based medicine criteria. This is particularly relevant in this field, as the quality of experimental methodology varies considerably among studies that are commonly cited in support of hypotheses to explain the aetiology of EAMC. Scientific evidence in support of the “electrolyte depletion” and “dehydration” hypotheses for the aetiology of EAMC comes mainly from anecdotal clinical observations, case series totalling 18 cases, and one small (n = 10) case–control study. Results from four prospective cohort studies do not support these hypotheses. In addition, the “electrolyte depletion” and “dehydration” hypotheses do not offer plausible pathophysiological mechanisms with supporting scientific evidence that could adequately explain the clinical presentation and management of EAMC. Scientific evidence for the “altered neuromuscular control” hypothesis is based on evidence from research studies in human models of muscle cramping, epidemiological studies in cramping athletes, and animal experimental data. Whilst it is clear that further evidence to support the “altered neuromuscular control” hypothesis is also required, research data are accumulating that support this as the principal pathophysiological mechanism for the aetiology of EAMC.
The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis
Authors: Roig M , O’Brien K , Kirk G , Murray R , McKinnon P , Shadgan B , Reid W D
Published: November 2008

The aim of this systematic review was to determine if eccentric exercise is superior to concentric exercise in stimulating gains in muscle strength and mass. Meta-analyses were performed for comparisons between eccentric and concentric training as means to improve muscle strength and mass. In order to determine the importance of different parameters of training, subgroup analyses of intensity of exercise, velocity of movement and mode of contraction were also performed. Twenty randomised controlled trials studies met the inclusion criteria. Meta-analyses showed that when eccentric exercise was performed at higher intensities compared with concentric training, total strength and eccentric strength increased more significantly. However, compared with concentric training, strength gains after eccentric training appeared more specific in terms of velocity and mode of contraction. Eccentric training performed at high intensities was shown to be more effective in promoting increases in muscle mass measured as muscle girth. In addition, eccentric training also showed a trend towards increased muscle cross-sectional area measured with magnetic resonance imaging or computerised tomography. Subgroup analyses suggest that the superiority of eccentric training to increase muscle strength and mass appears to be related to the higher loads developed during eccentric contractions. The specialised neural pattern of eccentric actions possibly explains the high specificity of strength gains after eccentric training. Further research is required to investigate the underlying mechanisms of this specificity and its functional significance in terms of transferability of strength gains to more complex human movements.
Validation of the New Zealand Physical Activity Questionnaire (NZPAQ-LF) and the International Physical Activity Questionnaire (IPAQ-LF) with accelerometry
Authors: Boon R M , Hamlin M J , Steel G D , Ross J J
Published: November 2008

Background

Validation of instruments used to measure physical activity patterns is essential when attempting to assess the effectiveness of physical activity interventions.

Objectives

To assess the validity of two self-report physical activity questionnaires on a representative sample of New Zealand adults.

Methods

70 adults aged 18–65 years from around Christchurch, New Zealand were required to wear an ActiGraph GT1M accelerometer during all waking hours for 7 consecutive days. Immediately following the 7 day accelerometer period participants were required to complete the long forms of both the New Zealand Physical Activity Questionnaire (NZPAQ-LF) and the International Physical Activity Questionnaire (IPAQ-LF).

Results

Both the NZPAQ-LF and the IPAQ-LF questionnaires showed small to moderate correlations with ActiGraph data for time spent in moderate-intensity physical activity (r=0.19–0.30) and total physical activity (sum of moderate and vigorous-intensity physical activity, r=0.30–0.32). In comparison with the ActiGraph data, both self-report questionnaires tended to overestimate activity levels by approximately 165%. Total physical activity levels gathered from both questionnaires were strongly correlated with each other (r=0.79) and showed good levels of agreement in the Bland–Altman plots.

Conclusions

The long forms of the NZPAQ and IPAQ were found to have acceptable validity when detecting participants' ability to meet activity guidelines based on exercise duration, but a significant amount of overestimation was evident. This presents a need for both instruments to be further developed and tested in order to increase validity.
A meta-analysis of impact exercise on postmenopausal bone loss: the case for mixed loading exercise programmes
Authors: Martyn-St James M , Carroll S
Published: November 2008

Objectives:

To assess the effects of differing impact exercise protocols on postmenopausal bone loss at the hip and spine.

Design:

Systematic review and meta-analysis.

Data sources:

Electronic bibliographic databases, key journals and reference lists of reviews and articles.

Review methods:

Two independent reviewers assessed controlled trials evaluating effects of impact exercise on lumbar spine, femoral neck and total hip bone mineral density (BMD) in postmenopausal women for inclusion. Heterogeneity amongst trials and publication bias were assessed. Trial quality assessment was also performed.

Results:

Impact protocols that included jogging mixed with walking and stair climbing, and protocols that incorporated impact exercise with high-magnitude loading (resistance exercises), were effective at lumbar spine (weighted mean difference (random effects) 0.025 g/cm295% CI (0.004 to 0.046) and 0.016 g/cm295% CI (0.005 to 0.027); p = 0.02 and p = 0.005 respectively), although heterogeneity was evident (I2 = 88% andI2 = 73%, whereI2measures the extent of inconsistency among the trials). Effects on femoral neck BMD following these types of protocols were significant (weighted mean difference (fixed effect) 0.022 g/cm295% CI (0.014 to 0.030); p<0.001 and 0.005 g/cm295% CI (0.001 to 0.010); p = 0.03 respectively). High-impact only and odd-impact only protocols were ineffective in increasing BMD at any site.

Conclusion:

Mixed loading exercise programmes combining jogging with other low-impact loading activity and programmes mixing impact activity with high-magnitude exercise as resistance training appear effective in reducing postmenopausal bone loss at the hip and spine. Other forms of impact exercise appear less effective at preserving BMD in this population. However, diverse methodological and reporting discrepancies are evident in current published trials.
Popular drugs in sport: descriptive analysis of the enquiries made via the Drug Information Database (DID)
Authors: Petróczi A , Naughton D P
Published: November 2008

Objective:

To analyse enquiries made in the Drug Information Database (DID) to develop a better understanding of athletes’ interests and concerns regarding the prohibited status of available substances.

Setting:

Retrospective analyses of anonymous enquiries recorded in the DID in 2006 and 2007.

Participants:

Athletes and supporting personnel.

Results:

The DID recorded 223 717 enquiries with 200 of the >6000 UK licensed pharmaceutical products receiving over 100 enquiries each. The majority (79.2%) of these enquiries were in the pharmaceutical product category, followed by recreational drugs (10.4%). A variety of common medications were subject to enquiry, with anti-inflammatory agents, decongestants and bronchodilators being most common; a trend in keeping with reported medication use by athletes. Of all enquiries, 42% were not found owing to misspelled words or enquiries about unregulated substances. The proportion of enquiries about substances not listed in the database is relatively high and has increased over the 24 month observation period.

Conclusion:

The DID is a well-used information resource with some 10 000 enquiries being made each month. Of the c. 60% of successful enquiries, the major focus was on pharmaceutical products. With some 73% of enquiries being made by the athletes themselves, further investigations are warranted to explore enquiry patterns in relation to specific sports. Of the unsuccessful enquiries, a large number were related to nutritional supplements, which warrants further investigation. The DID database appears to be a valid mirror of athletes’ chemically assisted practices and may be successfully used to inform health professionals as well as antidoping prevention programmes.
Eccentric exercises; why do they work, what are the problems and how can we improve them?
Authors: Rees J D , Wolman R L , Wilson A
Published: November 2008

Eccentric exercises (EE) have proved successful in the management of chronic tendinopathy, particularly of the Achilles and patellar tendons, where they have been shown to be effective in controlled trials. However, numerous questions regarding EE remain. The standard protocols are time-consuming and require very motivated patients. EE are effective in some tendinopathies but not others. Furthermore, the location of the lesion can have a profound effect on efficacy; for example, standard EE in insertional lesions of the Achilles are ineffective.

Until recently little was known of the effect of EE on tendinopathic tendons, although a greater understanding of this process is emerging. Additionally, recent in vivo evidence directly comparing eccentric and concentric exercises provides a possible explanation for the therapeutic benefit of EE. The challenge now is to make EE more effective. Suggestions on areas of future research are made.
Whole of community physical activity interventions: easier said than done
Authors: Mummery W K , Brown W J
Published: November 2008

Objectives:

To reflect on whole community intervention approaches to promoting physical activity, using experiences from the 10,000 Steps Rockhampton project.

Design:

Many studies are quasi-experimental with single site intervention and comparison communities.

Setting and participants:

Whole communities.

Intervention:

Coordinated multiple strategies designed to address individual, interpersonal and environmental determinants of physical activity.

Main outcome measure:

Physical activity

Results:

There are many challenges to conducting whole community interventions. Developing community partnerships and coalitions, reaching socially disadvantaged groups, and developing effective evaluation methods are identified as specific concerns.

Conclusions:

Despite the challenges, the whole community approach still offers tremendous potential for developing the social and cultural change which will be required for sustained improvements in population physical activity
PRUNING ARTIFICIAL NEURAL NETWORKS USING NEURAL COMPLEXITY MEASURES
Authors: JORGENSEN THOMAS D. , HAYNES BARRY P. , NORLUND CHARLOTTE C. F.
Published: November 2008

This paper describes a new method for pruning artificial neural networks, using a measure of the neural complexity of the neural network. This measure is used to determine the connections that should be pruned. The measure computes the information-theoretic complexity of a neural network, which is similar to, yet different from previous research on pruning. The method proposed here shows how overly large and complex networks can be reduced in size, whilst retaining learnt behaviour and fitness. The technique proposed here helps to discover a network topology that matches the complexity of the problem it is meant to solve. This novel pruning technique is tested in a robot control domain, simulating a racecar. It is shown, that the proposed pruning method is a significant improvement over the most commonly used pruning method Magnitude Based Pruning. Furthermore, some of the pruned networks prove to be faster learners than the benchmark network that they originate from. This means that this pruning method can also help to unleash hidden potential in a network, because the learning time decreases substantially for a pruned a network, due to the reduction of dimensionality of the network.
AN IMPROVEMENT OF EXTREME LEARNING MACHINE FOR COMPACT SINGLE-HIDDEN-LAYER FEEDFORWARD NEURAL NETWORKS
Authors: HUYNH HIEU TRUNG , WON YONGGWAN , KIM JUNG-JA
Published: November 2008

Recently, a novel learning algorithm called extreme learning machine (ELM) was proposed for efficiently training single-hidden-layer feedforward neural networks (SLFNs). It was much faster than the traditional gradient-descent-based learning algorithms due to the analytical determination of output weights with the random choice of input weights and hidden layer biases. However, this algorithm often requires a large number of hidden units and thus slowly responds to new observations. Evolutionary extreme learning machine (E-ELM) was proposed to overcome this problem; it used the differential evolution algorithm to select the input weights and hidden layer biases. However, this algorithm required much time for searching optimal parameters with iterative processes and was not suitable for data sets with a large number of input features. In this paper, a new approach for training SLFNs is proposed, in which the input weights and biases of hidden units are determined based on a fast regularized least-squares scheme. Experimental results for many real applications with both small and large number of input features show that our proposed approach can achieve good generalization performance with much more compact networks and extremely high speed for both learning and testing.
AN LMI APPROACH TO DESIGN H∞ CONTROLLERS FOR DISCRETE-TIME NONLINEAR SYSTEMS BASED ON UNIFIED MODELS
Authors: LIU MEIQIN , ZHANG SENLIN
Published: November 2008

A unified neural network model termed standard neural network model (SNNM) is advanced. Based on the robust L2 gain (i.e. robust H∞ performance) analysis of the SNNM with external disturbances, a state-feedback control law is designed for the SNNM to stabilize the closed-loop system and eliminate the effect of external disturbances. The control design constraints are shown to be a set of linear matrix inequalities (LMIs) which can be easily solved by various convex optimization algorithms (e.g. interior-point algorithms) to determine the control law. Most discrete-time recurrent neural network (RNNs) and discrete-time nonlinear systems modelled by neural networks or Takagi and Sugeno (T–S) fuzzy models can be transformed into the SNNMs to be robust H∞ performance analyzed or robust H∞ controller synthesized in a unified SNNM's framework. Finally, some examples are presented to illustrate the wide application of the SNNMs to the nonlinear systems, and the proposed approach is compared with related methods reported in the literature.
BLOOD CELL IDENTIFICATION USING A SIMPLE NEURAL NETWORK
Authors: KHASHMAN ADNAN
Published: November 2008

Classification of blood cell types can be time consuming and susceptible to error due to the different morphological features of the cells. This paper presents a blood cell identification system that simulates a human visual inspection and identification of the three blood cell types. The proposed system uses global pattern averaging to extract cell features, and a neural network to classify the cell type. Two neural networks are investigated and a comparison between these networks is drawn. Experimental results suggest that the proposed system provides fast, simple and efficient identification which can be used in automating laboratory reporting.
SWIFT OBSERVATIONS OF GAMMA-RAY BURSTS
Authors: GEHRELS NEIL
Published: November 2008

The Swift mission, launched on 20 November 2004, is detecting ~ 100 gamma-ray bursts (GRBs) each year, and immediately (within ~ 90 s) starting X-ray and UV/optical observations of the afterglow. It has already collected an impressive database including prompt emission to higher sensitivities than BATSE, uniform monitoring of afterglows, and rapid follow-up by other observatories notified through the Gamma-ray bursts Coordinates Network (GCN). The X-ray afterglows have been found to have complex temporal shapes including tails emission from the prompt phase and bright flares. X-ray and optical afterglow detections from short bursts have led to accurate localizations. It is found that they can occur in non-star forming galaxies or regions, whereas long GRBs are strongly concentrated within star forming regions. This is consistent with the NS merger model. Swift has greatly increased the redshift range of GRB detection. The highest redshift GRBs, at z ~ 5-6, are approaching the era of reionization. Ground-based deep optical spectroscopy of high redshift bursts is giving metallicity measurements and other information on the source environment to much greater distance than other techniques. The localization of GRB 060218 in a nearby galaxy, and association with SN 2006aj, added a valuable member to the class of GRBs with detected supernova. The prospects for future progress are excellent given the > 10 year orbital lifetime of the Swift satellite.
THE INTERPLAY OF PROMPT AND AFTERGLOW EMISSION IN GRB 060418
Authors: VERGANI S. D. , MALESANI D. , MOLINARI E.
Published: November 2008

We present observations of the early afterglow emission of GRB 060418. Thanks to the simultaneous coverage at optical, X-ray and gamma-ray wavelengths, we can detect and separate the external shock emission (visible in the optical and late X-ray data) and the central engine activity (early X and gamma rays). The two components are clearly distinguished based on temporal and spectral properties. The detection of the afterglow onset (in the optical) allows the determination of the fundamental fireball properties, namely its bulk Lorentz factor and total energy. The early time X-ray flare closely resembles the prompt emission gamma-ray pulses in its temporal profile, being wider at low energies and showing lags between the hard and soft bands. This provides a strong suggestion that X-ray flares are a continuation of the prompt emission.
GRB 070311: A COMMON ORIGIN FOR THE PROMPT AND AFTERGLOW EMISSION
Authors:   On behalf of a larger collaboration, VERGANI S. D. , GUIDORZI C.
Published: November 2008

GRB 070311 was a long burst that triggered INTEGRAL. We present prompt γ-ray, early NIR/optical, late optical and X-ray data on this burst and its afterglow. Interestingly, the H-band light curve acquired with REM exhibits two pulses at 80 and 140 s after the peak of the γ-ray burst, with possible evidence for a contemporaneous faint γ-ray tail. The late optical and X-ray afterglow underwent a rebrightening between 3 × 104 and 2 × 105 s after the burst with energy comparable with that of the prompt emission extrapolated in the X-ray band. After fitting the early γ-ray and optical light curves, we modelled the time profile of the late rebrightening as the time-rescaled version of the prompt γ-ray pulse over an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario.
DO ALL SHORT GRBs HAVE AN ASSOCIATED HOST GALAXY? THE CASE OF GRB 070707
Authors:   On behalf of the MISTICI collaboration, VERGANI S. D. , PIRANOMONTE S. , D'ELIA V. , ISRAEL G. L. , STELLA L. , MALESANI D. , D'AVANZO P. , CHINCARINI G. , FUGAZZA D. , COVINO S. , TAGLIAFERRI G.
Published: November 2008

We present optical observations of the short GRB 070707, discovered by INTEGRAL. The afterglow light-curve shows a very steep decay after ≈ 2 days from the trigger, which cannot be accounted for by jetted or high latitude emission. Thanks to very deep ESO–VLT observations, we detect a very faint host galaxy with R = 27.3 ± 0.13. This result confirms that short GRBs can be associated with very faint galaxies, and suggests that some associations with bright objects in the close vicinity of other short GRBs should be treated with caution.
SEARCH FOR NEARBY GALAXIES IN BATSE/IPN SHORT GRB ERROR BOXES
Authors: TIKHOMIROVA Y. , POZANENKO A. , HURLEY K.
Published: November 2008

Recent observations have shown an apparent association of short duration gamma-ray bursts with a variety of host galaxies at moderate redshifts. However, a statistical analysis with a large sample of BATSE GRBs indicates that at least some fraction of short GRBs originates in the local universe. We have considered pre-Swift well-localized short GRBs to examine a possible association of these bursts with galaxies at low redhsifts. We have used BATSE/IPN localizations of short bursts and SDSS DR5/PSCz catalogs as galaxies surveys.
A THREE-STAGE MODEL FOR THE INNER ENGINE OF GRBs: PROMPT EMISSION AND EARLY AFTERGLOW
Authors: STAFF J. , NIEBERGAL B. , OUYED R.
Published: November 2008

We describe a model within the "quark-nova" scenario to interpret the recent observations of early X-ray afterglows of long gamma-ray bursts (GRBs) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. STAGE 1 is an accreting (proto-) neutron star leading to a possible delay between the core collapse and the GRB. STAGE 2 is accretion onto a quark star, launching an ultrarelativistic jet generating the prompt GRB. This jet also creates the afterglow as the jet interacts with the surrounding medium creating an external shock. Slower shells ejected from the quark star (during accretion), can re-energize the external shock leading to a flatter segment in the X-ray afterglow. STAGE 3, which occurs only if the quark star collapses to form a black hole, consists of an accreting black hole. The jet launched in this accretion process interacts with the preceding quark star jet, and could generate the flaring activity frequently seen in early X-ray afterglows. Alternatively, a STAGE 2b can occur in our model if the quark star does not collapse to a black hole. The quark star in this case can then spin down due to magnetic braking, and the spin down energy may lead to flattening in the X-ray afterglow as well. This model seems to account for both the energies and the timescales of GRBs, in addition to the newly discovered early X-ray afterglow features.
OUTFLOWS FROM MAGNETOROTATIONAL SUPERNOVAE
Authors: MOISEENKO S. G. , BISNOVATYI-KOGAN G. S.
Published: November 2008

We discuss results of 2D simulations of magnetorotational (MR) mechanism of core collapse supernova explosions. Due to the nonuniform collapse, the collapsed core rotates differentially. In the presence of an initial poloidal magnetic field its toroidal component appears and grows with time. Increased magnetic pressure leads to the formation of a compression wave which moves outwards. It transforms into the fast MHD shock wave (supernova shock wave). The shape of the MR supernova explosion qualitatively depends on the configuration of the initial magnetic field. For a dipole-like initial magnetic field, the supernova explosion develops mainly along the rotational axis, forming a mildly collimated jet. A quadrupole-like initial magnetic field leads to the explosion developing mainly along the equatorial plane. The magnetorotational instability was found in our simulations. The supernova explosion energy grows with an increase of the initial core mass and rotational energy of the core, and corresponds to the observational data.
FILAMENTATION INSTABILITY OF INTERACTING CURRENT SHEETS IN STRIPED RELATIVISTIC WINDS: THE ORIGIN OF LOW SIGMA?
Authors: ARONS JONATHAN
Published: November 2008

I outline a mechanism, akin to Weibel instabilities of interpenetrating beams, in which the neighboring current sheets in a striped wind from an oblique rotator interact through a two stream-like mechanism (a Weibel instability in flatland), to create an anomalous resistivity that heats the sheets and causes the magnetic field to diffusively annihilate in the wind upstream of the termination shock. The heating has consequences for observable unpulsed emission from pulsars.
VERY HIGH ENERGY GAMMA-RAY MEASUREMENTS OF BLAZARS
Authors: GIEBELS BERRIE
Published: November 2008

The origin of γ-rays emitted by blazars is widely attributed to radiative cooling of the most energetic particles in a relativistic flow, which itself is thought to originate from the surroundings of a supermassive black hole. The linkage between the accreting gas, the black hole, jet formation, and the observed radiation from the jet, are still very difficult to establish. The most energetic γ-rays are likely to be produced close to the comptonizing particles acceleration zone, and are therefore a unique probe of the underlying physical mechanisms at play. This report contains a review of the status of the field of Very High Energy (VHE) γ-ray astronomy, in the light of measurements from the current generation of Atmospheric Čerenkov Telescopes (ACTs), which have dramatically changed our view of blazars over the last years, and given us new insights about the blazar phenomenon.
SIMULTANEOUS X-RAY/TeV OBSERVATIONS OF AN EXCEPTIONAL FLARE OF PKS 2155-304
Authors:   On behalf of the H.E.S.S. Collaboration, COSTAMANTE L.
Published: November 2008

On the night of 29–30 July 2006, a major γ-ray outburst occurred from PKS 2155-304, which was observed simultaneously with H.E.S.S., Chandra and the Bronberg optical telescopes. An overall 6–8 hours of simultaneous uninterrupted coverage was obtained. Here we report the first preliminary results of this exceptional dataset. The source showed correlated variability between the X-ray and VHE bands, with no lags. The spectra evolve with similar patterns. Huge VHE variations (~ 22×) are accompanied only by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (LC/LS ~ 10), and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge all known "standard" scenarios for the blazar emission.
TOWARDS A UNITARIAN VIEW OF CHANDRA JETS
Authors: SAMBRUNA R. M. , MARASCHI L. , TAVECCHIO F.
Published: November 2008

In almost a decade of operations, Chandra has observed and discovered the X-ray counterparts of several tens of extragalactic radio jets, with a variety of morphologies and SEDs. Here we take a fresh approach and assume that we do not know their relationship. We then search for phenomenological trends. While admittedly naive, this perspective allow us to start identifying key quantities towards a large-scale jet "unitarian view", just as was previously done for their compact, pc-scale cousins, the blazars. Similarly to the latter, we find that key parameters governing the properties of Chandra jets are their powers and the mass flux, the latter parameterizing the jet interaction with the ambient gas.
EMISSION FROM LARGE-SCALE JETS IN QUASARS
Authors: UCHIYAMA YASUNOBU
Published: November 2008

We consider the emission processes in the large-scale jets of powerful quasars based on the results obtained with the VLA, Spitzer, Hubble, and Chandra. We show that two archetypal jets, 3C 273 and PKS 1136–135, have two distinct spectral components on large-scales: (1) the low-energy (LE) synchrotron spectrum extending from radio to infrared, and (2) the high-energy (HE) component arising from optical and extending to X-rays. The X-ray emission in quasar jets is often attributed to inverse-Compton scattering of cosmic microwave background (CMB) photons by radio-emitting electrons in a highly relativistic jet. However, recent data prefer synchrotron radiation by a second distinct electron population as the origin of the HE component. We anticipate that optical polarimetry with Hubble will establish the synchrotron nature of the HE component. Gamma-ray observations with GLAST (renamed as the Fermi Gamma-ray Space Telescope), as well as future TeV observations, are expected to place important constraints on the jet models.
OPTICAL DEPTH FOR VHE γ-RAYS FROM DISTANT SOURCES FROM A GENERIC EBL DENSITY
Authors: RAUE M. , MAZIN D.
Published: November 2008

Very-high-energy (VHE; E > 100 GeV ) γ-rays from distant sources suffer attenuation through pair-production with low energy photons from the diffuse extragalactic photon fields in the ultraviolet (UV) to far-infrared (FIR) (commonly referred to as extragalactic background light; EBL). When modeling the intrinsic spectra of the VHE γ-ray sources it is crucial to correctly account for the attenuation. Unfortunately, direct measurements of the EBL are difficult and the knowledge about the EBL over certain wavelength ranges is poor. To calculate the EBL attenuation, usually predictions from theoretical models are used. Recently, the limits on the EBL from direct and indirect methods have narrowed down the possible EBL range and many of the previous models are in conflict with these limits. We propose a new generic EBL density (not a complete model), which is in compliance with the new EBL limits. EBL evolution with redshift is included in the calculation in a very simple but effective ad hoc way. Properties of this generic EBL are discussed.
A FRAMEWORK FOR INTERPRETING OBSERVED PHENOMENA ASSOCIATED WITH RELATIVISTIC OUTFLOWS IN AGN
Authors: GABUZDA D. C.
Published: November 2008

A growing number of jets in active galactic nuclei (AGN) show clear signs of helical magnetic (B) fields: Faraday-rotation gradients across the VLBI jets, extended regions of jet with orthogonal B fields, transverse polarization and total-intensity structures characteristic of helical fields, interknot polarization implying underlying orthogonal B fields, and a predominance of orthogonal B fields in the VLBI cores. In addition, a link has now been found between the circular polarization detected in AGN cores and the presence of helical jet B fields within these cores. This now abundant evidence compels us to take very seriously the idea that many, possibly all, AGN jets have helical B fields. As a whole, the recent observational results considered here suggest that we must look at AGN jets as fundamentally electromagnetic, current-carrying structures if we wish to fully understand their nature. This provides an overall framework for interpreting various observed phenomena associated with the relativistic jets of AGN, including high-energy phenomena. Superposed on the structure of the underlying helical B field may be the effects of relativistic shocks and interaction with the surrounding medium in some cases; these may dominate observed phenomena locally, while it is the "intrinsic" helical B field of the jet itself that determines the global observed characteristics of the jet.
INVESTIGATION OF CORRELATIONS BETWEEN THE OPTICAL AND VLBI CORE POLARIZATION OF AGN
Authors: ALGABA J. C. , GABUZDA D. C. , SMITH P. S.
Published: November 2008

The continua of highly active radio-loud AGN are dominated by synchrotron radiation over virtually the entire spectrum. Despite this fact, it has often been thought that no correlation between optical and radio polarization should be observed, based on the idea that the synchrotron radiation at very different wavelengths is emitted at very different regions in the jet. However, a clear correlation between the Faraday-rotation-corrected VLBI core radio polarization angle and the nearly simultaneously measured optical polarization angle was found by Gabuzda et al., suggesting that the optical and compact radio polarizations are more closely related than had been thought. We have obtained new data in order to investigate this question. Our preliminary results show that, although the optical and radio core polarizations of BL Lac objects are usually aligned, the behavior displayed by quasars is more complex, and some may involve additional phenomenology, such as internal or very high core Faraday rotation.
MAGNETIC FIELDS IN BLAZAR PC-SCALE JETS — POSSIBLE CONNECTION TO SPIN RATES OF BLACK HOLES?
Authors: KHARB P. , LISTER M. L. , SHASTRI P.
Published: November 2008

We re-examine the differences observed in the pc-scale magnetic field geometry of high and low optical polarization quasars (HPQs, LPRQs) using the MOJAVE sample. We find that, as previously reported, HPQ jets exhibit predominantly transverse B fields while LPRQ jets tend to display longitudinal B fields. We attempt to understand these results along with the different B field geometry observed in the low and high energy peaked BL Lacs (LBLs, HBLs) using a simple picture wherein the spinning central black holes in these AGNs influence the speed and strength of the jet components (spine, sheath). Higher spin rates in HPQs compared to LPRQs and in LBLs compared to HBLs could explain the different total radio powers, VLBI jet speeds, and the observed B field geometry in these AGN classes.
PARSEC-SCALE INVESTIGATION OF THE MAGNETIC FIELD STRUCTURE OF SEVERAL AGN JETS
Authors: O'SULLIVAN S. P. , GABUZDA D. C.
Published: November 2008

Multi-frequency (4.6, 5, 5.5, 8, 8.8, 13, 15, 22 & 43 GHz) polarization observations of six "blazars" were obtained on the American Very Long Baseline Array (VLBA) over a 24-hr period on 2 July 2006. Observing at several frequencies, separated by short and long intervals, enabled reliable determination of the distribution of Faraday rotation on a range of scales. In all cases the magnitude of the RM increases in the higher frequency observations, implying that the electron density and/or magnetic field strength is increasing as we get closer to the central engine. After correcting for Faraday rotation, the polarization orientation in the jet is either parallel or perpendicular to the jet direction. A transverse rotation measure (RM) gradient was detected in the jet of 0954+658, providing evidence for the presence of a helical magnetic field surrounding the jet. For three of the sources (0954+658, 1418+546, 2200+420), the sign of the RM in the core region changes in different frequency-intervals, indicating that the line-of-sight component of the magnetic field is changing with distance from the base of the jet. We suggest an explanation for this in terms of bends in a relativistic jet surrounded by a helical magnetic field; where there is no clear evidence for pc-scale bends, the same effect can be explained by an accelerating/decelerating jet.
DETECTION OF A RELIC X-RAY JET IN CYGNUS A
Authors: STEENBRUGGE K. C. , BLUNDELL K. M. , DUFFY P.
Published: November 2008

We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long linear feature seen in its counterlobe. This feature has a nonthermal spectrum and lies on the line connecting the brighter hotspot on the approaching side and the nucleus. We therefore conclude that this feature is (or was) a jet. However, the outer part of this X-ray jet does not trace the current counterjet observed in radio. No X-ray counterpart is observed on the jet side. Using light-travel time effects we conclude that this X-ray 50 kpc linear feature is a relic jet that contains enough low-energy plasma (γ ~ 103) to inverse-Compton scatter cosmic microwave background photons, producing emission in the X-rays.
PHOTON BREEDING MECHANISM IN RELATIVISTIC JETS: ASTROPHYSICAL IMPLICATIONS
Authors: POUTANEN J. , STERN B. E.
Published: November 2008

Photon breeding in relativistic jets involves multiplication of high-energy photons propagating from the jet into the external environment and back, with the conversion into electron-positron pairs. The exponential growth of the energy density of these photons is a supercritical process powered by the bulk energy of the jet. The efficient deceleration of the jet outer layers creates a structured jet morphology with a fast spine and slow sheath. In initially fast and high-power jets even the spine can be decelerated efficiently leading to very high radiative efficiencies of conversion of the jet bulk energy into radiation. The decelerating, structured jets have angular distribution of radiation significantly broader than that predicted by a simple blob model with a constant Lorentz factor. This reconciles the discrepancy between the high Doppler factors determined by the fits to the spectra of TeV blazars and the low apparent velocities observed at VLBI scales as well as the low jet Lorentz factors required by the observed statistics and luminosity ratio of Fanaroff-Riley I radio galaxies and BL Lac objects. Photon breeding produces a population of high-energy leptons in agreement with the constraints on the electron injection function required by spectral fits of the TeV blazars. Relativistic pairs created outside the jet and emitting gamma-rays by the inverse Compton process might explain the relatively high level of TeV emission from the misaligned jet in the radio galaxies. The mechanism reproduces basic spectral features observed in blazars including the blazar sequence (shift of the spectral peaks towards lower energies with increasing luminosity). The mechanism is very robust and can operate in various environments characterized by the high photon density.
ELECTRON THERMALIZATION AND PHOTON EMISSION FROM MAGNETIZED COMPACT SOURCES
Authors: VURM INDREK , POUTANEN JURI
Published: November 2008

We present detailed calculations of the electron thermalization by synchrotron self-absorption accounting for cooling by Compton scattering. For the first time, we solve the coupled kinetic equations for electrons and photons without any approximations on the relevant cross-sections and compute self-consistently the resulting electron and photon distributions. The results presented in this contribution may be applied to the magnetized coronae around galactic black hole accretion disks.
THE ENGINE OF OUTFLOWS IN AGN: THE ROLE OF PHYSICAL TURBULENT VISCOSITY
Authors: CASSARO P. , SCHILLIRÓ F. , COSTA V. , BELVEDERE G. , ZAPPALÁ R. A. , LANZAFAME G.
Published: November 2008

Adopting the smoothed particle hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D, axially symmetric, physically viscous accretion disc around a black hole (BH) in an AGN. In such disc models, the role of the specific angular momentum λ and of the physical turbulent viscosity parameter α, according to the Shakura and Sunyaev prescription, are examined. One or two shock fronts develop in the radial inviscid flow, according to the assigned initial kinematic and thermodynamic conditions. Couples of (α, λ) values determine radial periodical oscillations in the shock front. An outflow can develop from the subsonic post shock region, close to the black hole, in some cases. This provides evidence for a link between the accretion disc and the fueling of a jet, through the presence of shock fronts in an accretion disc close to the centrifugal barrier.