10,598 research outputs found
The origin of the positron excess in cosmic rays
We show that the positron excess measured by the PAMELA experiment in the
region between 10 and 100 GeV may well be a natural consequence of the standard
scenario for the origin of Galactic cosmic rays. The 'excess' arises because of
positrons created as secondary products of hadronic interactions inside the
sources, but the crucial physical ingredient which leads to a natural
explanation of the positron flux is the fact that the secondary production
takes place in the same region where cosmic rays are being accelerated.
Therefore secondary positrons (and electrons) participate in the acceleration
process and turn out to have a very flat spectrum, which is responsible, after
propagation in the Galaxy, for the observed positron 'excess'. This effect
cannot be avoided though its strength depends on the values of the
environmental parameters during the late stages of evolution of supernova
remnants.Comment: 4 Pages, 2 figures. Some references and discussion adde
Unraveling Orbital Correlations via Magnetic Resonant Inelastic X-ray Scattering
Although orbital degrees of freedom are a factor of fundamental importance in
strongly correlated transition metal compounds, orbital correlations and
dynamics remain very difficult to access, in particular by neutron scattering.
Via a direct calculation of scattering amplitudes we show that instead magnetic
resonant inelastic x-ray scattering (RIXS) does reveal orbital correlations. In
contrast to neutron scattering, the intensity of the magnetic excitations in
RIXS depends very sensitively on both the symmetry of the orbitals that spins
occupy, and on photon polarizations. We show in detail how this effect allows
magnetic RIXS to distinguish between alternating orbital ordered and
ferro-orbital (or orbital liquid) states.Comment: 7 pages, 4 figures. Supplemental material adde
A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves
We present a correlation between the average temporal decay
({\alpha}X,avg,>200s) and early-time luminosity (LX,200s) of X-ray afterglows
of gamma-ray bursts as observed by Swift-XRT. Both quantities are measured
relative to a rest frame time of 200 s after the {\gamma}-ray trigger. The
luminosity average decay correlation does not depend on specific temporal
behavior and contains one scale independent quantity minimizing the role of
selection effects. This is a complementary correlation to that discovered by
Oates et al. (2012) in the optical light curves observed by Swift-UVOT. The
correlation indicates that on average, more luminous X-ray afterglows decay
faster than less luminous ones, indicating some relative mechanism for energy
dissipation. The X-ray and optical correlations are entirely consistent once
corrections are applied and contamination is removed. We explore the possible
biases introduced by different light curve morphologies and observational
selection effects, and how either geometrical effects or intrinsic properties
of the central engine and jet could explain the observed correlation.Comment: Accepted for Publication in ApJ; 16 pages, 15 figures, 2 table
GRB Flares: UV/Optical Flaring (Paper I)
We present a new algorithm for the detection of flares in gamma-ray burst
(GRB) light curves and use this algorithm to detect flares in the UV/optical.
The algorithm makes use of the Bayesian Information Criterion (BIC) to analyze
the residuals of the fitted light curve, removing all major features, and to
determine the statistically best fit to the data by iteratively adding
additional `breaks' to the light curve. These additional breaks represent the
individual components of the detected flares: T_start, T_stop, and T_peak. We
present the detection of 119 unique flaring periods detected by applying this
algorithm to light curves taken from the Second Swift Ultraviolet/Optical
Telescope (UVOT) GRB Afterglow Catalog. We analyzed 201 UVOT GRB light curves
and found episodes of flaring in 68 of the light curves. For those light curves
with flares, we find an average number of ~2 flares per GRB. Flaring is
generally restricted to the first 1000 seconds of the afterglow, but can be
observed and detected beyond 10^5 seconds. More than 80% of the flares detected
are short in duration with Delta t/t of < 0.5. Flares were observed with flux
ratios relative to the underlying light curve of between 0.04 to 55.42. Many of
the strongest flares were also seen at greater than 1000 seconds after the
burst.Comment: Submitted to ApJ. 20 pages (including 8 figures and 1 table
Electromagnetic pulse forming technology
The electromagnetic pulse forming technology (EMPT) provides substantial technological benefits with respect to tube forming and joining operations. However, in the past this technology was mainly adapted in academics, military production and small batch size productions. Establishing this technology in the world of civil-industrial mass production demands for several key prerequisites to be fulfilled. This report lists these requirements and moreover provides answers on ways for their completion
Correlated Nanoscopic Josephson Junctions
We discuss correlated lattice models with a time-dependent potential across a
barrier and show how to implement a Josephson-junction-like behavior. The
pairing occurs by a correlation effect enhanced by the symmetry of the system.
In order to produce the effect we need a mild distortion which causes avoided
crossings in the many-body spectrum. The Josephson-like response involves a
quasi-adiabatic evolution in the time-dependent field. Besides, we observe an
inverse-Josephson (Shapiro) current by applying an AC bias; a supercurrent in
the absence of electromotive force can also be excited. The qualitative
arguments are supported by explicit exact solutions in prototype 5-atom
clusters with on-site repulsion. These basic units are then combined in
ring-shaped systems, where one of the units sits at a higher potential and
works as a barrier. In this case the solution is found by mapping the
low-energy Hamiltonian into an effective anisotropic Heisenberg chain. Once
again, we present evidence for a superconducting flux quantization, i.e. a
Josephson-junction-like behavior suggesting the build-up of an effective order
parameter already in few-electron systems. Some general implications for the
quantum theory of transport are also briefly discussed, stressing the
nontrivial occurrence of asymptotic current oscillations for long times in the
presence of bound states.Comment: 12 pages, 2 figures, to appear in J. Phys. - Cond. Ma
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Latanoprost with high precision, piezo-print microdose delivery for IOP lowering: clinical results of the PG21 study of 0.4 µg daily microdose.
Background:Topical high-precision piezo-print delivery of microdoses of latanoprost achieved significant IOP reduction consistent with the eyedropper effect but with a 75% reduced exposure to drugs and preservatives. Prostaglandin analogs are a mainstay glaucoma therapy. However, conventional eyedroppers deliver 30-50 µL drops that greatly exceed the physiologic 7-µL ocular tear film capacity. Eyedropper overdosing floods the eye with excess drug compounds and preservatives, resulting in ocular surface toxicity, periorbitopathy, and other well-characterized ocular side effects. Piezoelectric high-precision microdosing provides targeted delivery that can reduce exposure to both drug and preservatives compared to conventional eyedropper delivery, with the potential to deliver similar biologic effect. Methods:Both eyes (N=60) of 30 healthy volunteers received single 8-µL microdoses of 0.005% latanoprost (0.4 µg; µRx-latanoprost) on the morning of Days 1 and 2 using a high-precision, piezo-print horizontal delivery system. Diurnal IOP was measured before and 2 days after microdosing. Main efficacy outcomes were diurnal IOP change after µRx-latanoprost microdosing and accurate microdosing success rates, and the primary safety outcome was adverse event (AE) incidence. Results:µRx-latanoprost reduced baseline IOP by 26% and 30% at 1 and 2 days postadministration, respectively. Successful topical dosing was achieved in 100% of technician-assisted deliveries. All patients successfully self-administered microdoses after receiving training. Microdose administration was well tolerated and did not result in any AEs. Conclusion:Microdosing of 0.4 µg of µRx-latanoprost achieved significant IOP reduction. Lower ocular exposure with topical prostaglandin analog microdosing can enable new therapeutic opportunities for optimizing glaucoma treatment. Microdosing may also be beneficial in reducing ocular side effects associated with excessive drug product and preservatives often used to treat chronic ocular diseases such as glaucoma
Comorbid depressive disorders in ADHD. the role of ADHD severity, subtypes and familial psychiatric disorders
ObjectiveaaTo evaluate the presence of Major Depressive Disorder (MDD) and Dysthymic Disorder (DD) in a sample of Italian children with Attention Deficit Hyperactivity Disorder (ADHD) and to explore specific features of comorbid depressive disorders in ADHD. MethodsaaThree hundred and sixty-six consecutive, drug-naïve Caucasian Italian outpatients with ADHD were recruited and comorbid disorders were evaluated using DSM-IV-TR criteria. To evaluate ADHD severity, parents of all children filled out the ADHD Rating Scale. Thirty-seven children with comorbid MDD or DD were compared with 118 children with comorbid conduct disorder and 122 without comorbidity for age, sex, IQ level, family psychiatric history, and ADHD subtypes and severity. Resultsaa42 of the ADHD children displayed comorbid depressive disorders: 16 exhibited MDD, 21 DD, and 5 both MDD and DD. The frequency of hyperactive-impulsive subtypes was significantly lower in ADHD children with depressive disorders, than in those without any comorbidity. ADHD children with depressive disorders showed a higher number of familial psychiatric disorders and higher score in the Inattentive scale of the ADHD Rating Scale, than children without any comorbidity. No differences were found for age, sex and IQ level between the three groups. Conclusions: Consistent with previous studies in other countries, depressive disorders affect a significant proportion of ADHD children in Italy. Patient assessment and subsequent treatment should take into consideration the possible presence of this comorbidity, which could specifically increase the severity of ADHD attention problems
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Hypertensive phase and early complications after Ahmed glaucoma valve implantation with intraoperative subtenon triamcinolone acetonide
Objective: To evaluate intraoperative subtenon triamcinolone acetonide (TA) as an adjunct to Ahmed glaucoma valve (AGV) implantation. Design: Retrospective comparative case series. Participants: Forty-two consecutive cases of uncontrolled glaucoma undergoing AGV implantation: 19 eyes receiving intraoperative subtenon TA and 23 eyes that did not receive TA. Methods: A retrospective chart review was performed on consecutive pseudophakic adult patients with uncontrolled glaucoma undergoing AGV with and without intraoperative subtenon TA injection by a single surgeon. Clinical data were collected from 42 eyes and analyzed for the first 6 months after surgery. Main outcome measures Primary outcomes included intraocular pressure (IOP) and number of glaucoma medications prior to and after AGV implantation. The hypertensive phase (HP) was defined as an IOP measurement of greater than 21 mmHg (with or without medications) during the 6-month postoperative period that was not a result of tube obstruction, retraction, or malfunction. Postoperative complications and visual acuity were analyzed as secondary outcome measures. Results: Five out of 19 (26%) TA cases and 12 out of 23 (52%) non-TA cases developed the HP (P=0.027). Mean IOP (14.2±4.6 in TA cases versus [vs] 14.7±5.0 mmHg in non-TA cases; P=0.78), and number of glaucoma medications needed (1.8±1.3 in TA cases vs 1.6±1.1 in the comparison group; P=0.65) were similar between both groups at 6 months. Although rates of serious complications did not differ between the groups (13% in the TA group vs 16% in the non-TA group), early tube erosion (n=1) and bacterial endophthalmitis (n=1) were noted with TA but not in the non-TA group. Conclusions: Subtenon TA injection during AGV implantation may decrease the occurrence of the HP but does not alter the ultimate IOP outcome and may pose increased risk of serious complications within the first 6 months of surgery
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