2,028 research outputs found
A multiscale view on inverse statistics and gain/loss asymmetry in financial time series
Researchers have studied the first passage time of financial time series and
observed that the smallest time interval needed for a stock index to move a
given distance is typically shorter for negative than for positive price
movements. The same is not observed for the index constituents, the individual
stocks. We use the discrete wavelet transform to illustrate that this is a long
rather than short time scale phenomenon -- if enough low frequency content of
the price process is removed, the asymmetry disappears. We also propose a new
model, which explain the asymmetry by prolonged, correlated down movements of
individual stocks
Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports
We demonstrate a new class of hollow-core Bragg fibers that are composed of
concentric cylindrical silica rings separated by nanoscale support bridges. We
theoretically predict and experimentally observe hollow-core confinement over
an octave frequency range. The bandwidth of bandgap guiding in this new class
of Bragg fibers exceeds that of other hollow-core fibers reported in the
literature. With only three rings of silica cladding layers, these Bragg fibers
achieve propagation loss of the order of 1 dB/m.Comment: 9 pages including 5 figure
Metal Enrichment of the Intergalactic Medium in Cosmological Simulations
Observations have established that the diffuse intergalactic medium (IGM) at
z ~ 3 is enriched to ~0.1-1% solar metallicity and that the hot gas in large
clusters of galaxies (ICM) is enriched to 1/3-1/2 solar metallicity at z=0.
Metals in the IGM may have been removed from galaxies (in which they presumably
form) during dynamical encounters between galaxies, by ram-pressure stripping,
by supernova-driven winds, or as radiation-pressure driven dust efflux. This
study develops a method of investigating the chemical enrichment of the IGM and
of galaxies, using already completed cosmological simulations. To these
simulations, we add dust and (gaseous) metals, distributing the dust and metals
in the gas according to three simple parameterized prescriptions, one for each
enrichment mechanism. These prescriptions are formulated to capture the basic
ejection physics, and calibrated when possible with empirical data. Our results
indicate that dynamical removal of metals from >~ 3*10^8 solar mass galaxies
cannot account for the observed metallicity of low-column density Ly-alpha
absorbers, and that dynamical removal from >~ 3*10^10 solar mass galaxies
cannot account for the ICM metallicities. Dynamical removal also fails to
produce a strong enough mass-metallicity relation in galaxies. In contrast,
either wind or radiation-pressure ejection of metals from relatively large
galaxies can plausibly account for all three sets of observations (though it is
unclear whether metals can be distributed uniformly enough in the low-density
regions without overly disturbing the IGM, and whether clusters can be enriched
quite as much as observed). We investigate in detail how our results change
with variations in our assumed parameters, and how results for the different
ejection processes compare. (Abridged)Comment: Minor revision, 1 figure added addressing diffusion of metals after
their ejection. Accepted by ApJ. 31 EmulateApj Pages with 13 embedded
postscript figure
Biopsy-based optimization and calibration of a signal-intensity-ratio-based MRI method (1.5 Tesla) in a dextran-iron loaded mini-pig model, enabling estimation of very high liver iron concentrations
OBJECTIVE: Magnetic resonance imaging (MRI)-based techniques for non-invasive assessing liver iron concentration (LIC) in patients with iron overload have a limited upper measuring range around 35 mg/g dry weight, caused by signal loss from accelerated T1-, T2-, T2* shortening with increasing LIC. Expansion of this range is necessary to allow evaluation of patients with very high LIC. AIM: To assess measuring range of a gradient-echo R2* method and a T1-weighted spin-echo (SE), signal intensity ratio (SIR)-based method (TE = 25 ms, TR = 560 ms), and to extend the upper measuring range of the SIR method by optimizing echo time (TE) and repetition time (TR) in iron-loaded minipigs. METHODS: Thirteen mini pigs were followed up during dextran-iron loading with repeated percutaneous liver biopsies for chemical LIC measurement and MRIs for parallel non-invasive estimation of LIC (81 examinations) using different TEs and TRs. RESULTS: SIR and R2* method had similar upper measuring range around 34 mg/g and similar method agreement. Using TE = 12 ms and TR = 1200 ms extended the upper measuring range to 115 mg/g and yielded good method of agreement. DISCUSSION: The wider measuring range is likely caused by lesser sensitivity of the SE sequence to iron, due to shorter TE, leading to later signal loss at high LIC, allowing evaluation of most severe hepatic iron overload. Validation in iron-loaded patients is necessary
Two X-Ray Bright Cataclysmic Variables with Unusual Activities: GZ Cnc and NSV 10934
We report on a discovery of unexpected activities in two X-ray bright dwarf novae. GZ Cnc showed an anomalous clustering of outbursts in 2002, in contrast to a low outburst frequency in the past record. The activity resembles an increased activity seen in some intermediate polars or candidates. We identified NSV 10934, X-ray selected high-amplitude variable star, as a dwarf nova with unusually rapid decline. The outburst characteristics make NSV 10934 a twin of recently discovered intermediate polar (HT Cam) with dwarf nova-type outbursts. We propose that these activities in X-ray strong dwarf novae may be a previously overlooked manifestation of outburst activities in magnetic cataclysmic variables
Houshold-level studies of forests and poverty in Burkina Faso:contextual information, methods and preliminary results
Psychological Flexibility as a Buffer against Caregiver Distress in Families with Psychosis
Background: Research has shown that caregivers of persons with psychosis play an invaluable role in recovery, but unfortunately, often report high levels of distress. While cognitive models of caregiver distress have been well-supported, there is still limited knowledge of the psychological factors involved. Recent advances in cognitive behavioral therapy seem to converge on the importance of acceptance- and mindfulness based processes.Aim: To examine the impact of psychological flexibility on caregiver distress in the early phases of psychosis, while controlling for known predictors of caregiver distress.Method: Within a cross-sectional design, 101 caregivers of 38 persons with first-episode psychosis in a clinical epidemiological sample completed a series of self-report measures.Results: A linear mixed model analysis found that, after controlling for caregiver socio-demographic factors, service user symptoms, drug use and global functioning, psychological flexibility was a significant predictor of caregiver distress.Conclusion: Greater level of psychological flexibility in caregivers, seems to be related to lower levels of caregiver distress. This finding corresponds to studies within a broad range of emotional disorders. There may be important clinical implications in terms of facilitating the process of acceptance through interventions from the ‘third-wave’ or contextual cognitive behavioral therapies
Schistosoma haematobium and soil-transmitted Helminths in Tana Delta District of Kenya:infection and morbidity patterns in primary schoolchildren from two isolated villages
BACKGROUND: Schistosomes and soil-transmitted helminths (STH) (hookworm, Trichuris trichiura and Ascaris lumbricoides) are widely distributed in developing countries where they infect over 230 million and 1.5 billion people, respectively. The parasites are frequently co-endemic and many individuals are co-infected with two or more of the species, but information on how the parasites interact in co-infected individuals is scarce. The present study assessed Schistosoma haematobium and STH infection and morbidity patterns among school children in a hyper-endemic focus in the Tana River delta of coastal Kenya. METHODS: Two hundred and sixty-two children aged 5–12 years from two primary schools were enrolled in the study. For each child, urine was examined for S. haematobium eggs and haematuria, stool was examined for STH eggs, peripheral blood was examined for eosinophilia and haemoglobin level, the urinary tract was ultrasound-examined for S. haematobium-related pathology, and the height and weight was measured and used to calculate the body mass index (BMI). RESULTS: Prevalences of S. haematobium, hookworm, T. trichiura and A. lumbricoides infection were 94, 81, 88 and 46 %, respectively. There was no significant association between S. haematobium and STH infection but intensity of hookworm infection significantly increased with that of T. trichiura. Lower BMI scores were associated with high intensity of S. haematobium (difference =−0.48, p > 0.05) and A. lumbricoides (difference =−0.67, p < 0.05). Haematuria (both macro and micro) was common and associated with S. haematobium infection, while anaemia was associated with high intensity of S. haematobium (OR = 2.08, p < 0.05) and high hookworm infections OR = 4.75; p < 0.001). The majority of children had eosinophilia, which was significantly associated with high intensity of hookworm infection (OR = 5.34, p < 0.05). Overall 38 % of the children had ultrasound-detectable urinary tract morbidity, which was associated with high intensity of S. haematobium infection (OR = 3.13, p < 0.05). CONCLUSION: Prevalences of S. haematobium and STH infections among the primary school children were high and the parasites were responsible for significant morbidity. A clear synergistic interaction was observed between hookworm and T. trichiura infections. Increased coverage in administration of praziquantel and albendazole in the area is recommended to control morbidity due to these infections
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