690 research outputs found
Herstellung von Nanometer-Strukturen mittels feinfokussiertem Ionenstrahl (FIB)
Feinfokussierte Ionenstrahlen dienen in den Gebieten der Halbleiterindustrie und Materialforschung der Mikro- und Nanostrukturierung. Die vorliegende Arbeit beschĂ€ftigt sich mit den beiden Hauptanwendungen von fokussierten Ionenstrahlen, dem Materialabtrag und der ionenstrahlinduzierten Materialabscheidung. Dabei wird die hochauflösende IonensĂ€ule CANION 31Z der Firma Orsay Physics mit Stromdichten von bis zu 10 A/cm2 und mit integriertem Gassystem eingesetzt. Es wird ausfĂŒhrlich auf Anwendungsbeispiele von Fokussierten Ionenstrahlsystemen im Bereich der Industrie und Forschung eingegangen. SchwerpunktmĂ€Ăig wird die Abscheidung von Wolfram aus dem Precursorgas W(CO)6 (Wolframhexacarbonyl) auf Si und SiO2 als Substrat untersucht, mit dem Ziel, gut leitfĂ€hige DrĂ€hte (hier im Sinne von Leiterbahnen) mit minimalem Querschnitt herzustellen. Die Optimierung der Ionenstrahl-Parameter dieser Feinfokussierten Ionenstrahlanlage bezĂŒglich der Abscheidung steht im Vordergrund. Dabei wird ein kurzer Einblick in die Theorie der Schichtentstehung beim Abscheidevorgang gegeben. Untersuchungen der erzeugten Strukturen entsprechend der SchichtqualitĂ€t und der Strukturabmessungen werden erlĂ€utert und die Ergebnisse diskutiert. Es konnten WolframdrĂ€hte mit einer LĂ€nge von 20 ... 100 ”m, einer Breite von minimal 150 nm und einer Höhe von maximal 600 nm angefertigt werden. Die Zusammensetzung der DrĂ€hte in AbhĂ€ngigkeit der Prozessparameter wurde mittels AES bestimmt. Im optimalen Fall wurden die Schichtanteile zu 80% W, 5% O, 6% C und 9% Ga ermittelt (Angaben in Atomprozent). Der spezifische Widerstand der WolframdrĂ€hte ist im Bereich 150 ... 320 ”Wcm gemessen worden
Point-like gamma ray sources as signatures of distant accelerators of ultra high energy cosmic rays
We discuss the possibility of observing distant accelerators of ultra high
energy cosmic rays in synchrotron gamma rays. Protons propagating away from
their acceleration sites produce extremely energetic electrons during
photo-pion interactions with cosmic microwave background photons. If the
accelerator is embedded in a magnetized region, these electrons will emit high
energy synchrotron radiation. The resulting synchrotron source is expected to
be point-like and detectable in the GeV-TeV energy range if the magnetic field
is at the nanoGauss level.Comment: 4 pages 2 figures. To be published in PR
Analyzing the Multiwavelength Spectrum and Variability of BL Lacertae During the July 1997 Outburst
The multiwavelength spectrum of BL Lacertae during its July 1997 outburst is
analyzed in terms of different variations of the homogeneous leptonic jet model
for the production of high-energy radiation from blazars. We find that a
two-component gamma-ray spectrum, consisting of a synchrotron self-Compton and
an external Compton component, is required in order to yield an acceptable fit
to the broadband spectrum. Our analysis indicates that in BL Lac, unlike other
BL Lac objects, the broad emission line region plays an important role for the
high-energy emission. Several alternative blazar jet models are briefly
discussed. In the appendix, we describe the formalism in which the process of
Comptonization of reprocessed accretion disk photons is treated in the
previously developed blazar jet simulation code which we use.Comment: Now accepted for publication in The Astronomical Journal.
Significantly extended discussion w.r.t. original version. 3 Figures included
using epsf.sty, rotate.st
The Radio to Gamma Ray Connection of EGRET Blazars: Correlation, Regression and Monte Carlo Analysis
A comprehensive statistical analysis of the broadband properties of EGRET
blazars is presented. This analysis includes sources identified as blazars in
the Sowards-Emmerd publications. Using this sample of 122 sources, we find that
there is a relationship as well as a
correlation between and , and a correlation between
radio luminosity and . Through the use of Monte Carlo simulations,
we can replicate the observed luminosity relationship if a synchrotron
self-Compton model is assumed. However, this relationship can not be replicated
if an external Compton scattering model is assumed. These differences are
primarily due to beaming effects.
In addition it has been determined that the intrinsic radio luminosity of the
parent sample falls in the range
and that the bulk Lorentz factors of the source are in the range , in a agreement with VLBI observations.
Finally, we discuss implications for GLAST, successfully launched in June
2008
EGRET Observations of the Extragalactic Gamma Ray Emission
The all-sky survey in high-energy gamma rays (E30 MeV) carried out by the
Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray
Observatory provides a unique opportunity to examine in detail the diffuse
gamma-ray emission. The observed diffuse emission has a Galactic component
arising from cosmic-ray interactions with the local interstellar gas and
radiation as well an almost uniformly distributed component that is generally
believed to originate outside the Galaxy. Through a careful study and removal
of the Galactic diffuse emission, the flux, spectrum and uniformity of the
extragalactic emission is deduced. The analysis indicates that the
extragalactic emission is well described by a power law photon spectrum with an
index of -(2.10+-0.03) in the 30 MeV to 100 GeV energy range. No large scale
spatial anisotropy or changes in the energy spectrum are observed in the
deduced extragalactic emission. The most likely explanation for the origin of
this extragalactic high-energy gamma-ray emission is that it arises primarily
from unresolved gamma-ray-emitting blazars.Comment: 19 pages latex, 10 figures, accepted for publication in Ap
The AGASA/SUGAR Anisotropies and TeV Gamma Rays from the Galactic Center: A Possible Signature of Extremely High-energy Neutrons
Recent analysis of data sets from two extensive air shower cosmic ray
detectors shows tantalizing evidence of an anisotropic overabundance of cosmic
rays towards the Galactic Center (GC) that ``turns on'' around eV. We
demonstrate that the anisotropy could be due to neutrons created at the
Galactic Center through charge-exchange in proton-proton collisions, where the
incident, high energy protons obey an power law associated with
acceleration at a strong shock. We show that the normalization supplied by the
gamma-ray signal from EGRET GC source 3EG J1746-2851 -- ascribed to pp induced
neutral pion decay at GeV energies -- together with a very reasonable spectral
index of 2.2, predicts a neutron flux at eV fully consistent
with the extremely high energy cosmic ray data. Likewise, the normalization
supplied by the very recent GC data from the HESS air-Cerenkov telescope at
\~TeV energies is almost equally-well compatible with the eV
cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be
themselves incompatible. We consider the implications of this discrepancy. We
discuss why the Galactic Center environment can allow diffusive shock
acceleration at strong shocks up to energies approaching the ankle in the
cosmic ray spectrum. Finally, we argue that the shock acceleration may be
occuring in the shell of Sagittarius A East, an unusual supernova remnant
located very close to the Galactic Center. If this connection between the
anisotropy and Sagittarius A East could be firmly established it would be the
first direct evidence for a particular Galactic source of cosmic rays up to
energies near the ankle.Comment: 57 pages, 2 figure
Early postpartum restingâstate functional connectivity for mothers receiving buprenorphine treatment for opioid use disorder: A pilot study
Between 1999 and 2014, the prevalence of opioid use disorder (OUD) among pregnant women quadrupled in the USA. The standard treatment for peripartum women with OUD is buprenorphine. However, the maternal behavior neurocircuit that regulates maternal behavior and motherâinfant bonding has not been previously studied for human mothers receiving buprenorphine treatment for OUD (BT). Rodent research shows opioid effects on reciprocal inhibition between maternal care and defence maternal brain subsystems: the hypothalamus and periaqueductal gray, respectively. We conducted a longitudinal functional magnetic resonance imaging (fMRI) pilot study in humans to specifically examine restingâstate functional connectivity (rsâFC) between the periaqueductal gray and hypothalamus, as well as to explore associations with maternal bonding for BT. We studied 32 mothers who completed fMRI scans at 1Â month (T1) and 4Â months postpartum (T2), including seven mothers receiving buprenorphine for OUD and 25 nonâOUD mothers as a comparison group (CG). The participants underwent a 6âminute restingâstate fMRI scan at each time point. We measured potential bonding impairments using the Postpartum Bonding Questionnaire to explore how rsâFC with periaqueductal gray is associated with bonding impairments. Compared to CG, BT mothers differed in periaqueductal grayâdependent rsâFC with the hypothalamus, amygdala, insular cortex and other brain regions at T1, with many of these differences disappearing at T2, suggesting potential therapeutic effects of continuing buprenorphine treatment. In contrast, the ârejection and pathological angerâ subscale of the Postpartum Bonding Questionnaire at T1 and T2 was associated with the T1âtoâT2 increases in periaqueductal grayâdependent rsâFC with the hypothalamus and amygdala. Preliminary evidence links maternal bonding problems for mothers with OUD early in the postpartum to connectivity between specific care and defence maternal brain circuits, which may be mitigated by buprenorphine treatment. This exploratory study supports a potential mechanism for investigating both the therapeutic benefits and risks of opioids for maternal care and bonding with infants.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151866/1/jne12770.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151866/2/jne12770_am.pd
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