18,577 research outputs found
ROSAT Detection and High Precision Localization of X-ray Sources in the November 19, 1978 Gamma-Ray Burst Error Box
We report on observations of the 1978, November 19 Gamma-Ray Burst source,
performed with the ROSAT X-ray HRI experiment. Two sources were detected, one
of which is possibly variable. The latter source is identical to the source
discovered in 1981 by the EINSTEIN satellite, and recently detected by ASCA.
The precise localization of these sources is given, and our data are compared
with optical, radio and previous X-ray data.Comment: 10 pages with 2 figures, Accepted for publication in the
Astrophysical Journal (Letters), Latex, aastex macros neede
High field CdS detector for infrared radiation
New and highly sensitive method of detecting infrared irradiation makes possible solid state infrared detector which is more sensitive near room temperature than usual photoconductive low band gap semiconductor devices. Reconfiguration of high field domains in cadmium sulphide crystals provides basis for discovery
High field CdS detector for infrared radiation
An infrared radiation detector including a cadmium sulfide platelet having a cathode formed on one of its ends and an anode formed on its other end is presented. The platelet is suitably doped such that stationary high-field domains are formed adjacent the cathode when based in the negative differential conductivity region. A negative potential is applied to the cathode such that a high-field domain is formed adjacent to the cathode. A potential measuring probe is located between the cathode and the anode at the edge of the high-field domain and means are provided for measuring the potential at the probe whereby this measurement is indicative of the infrared radiation striking the platelet
Hands-On Universe: A Global Program for Education and Public Outreach in Astronomy
Hands-On Universe (HOU) is an educational program that enables students to
investigate the Universe while applying tools and concepts from science, math,
and technology. Using the Internet, HOU participants around the world request
observations from an automated telescope, download images from a large image
archive, and analyze them with the aid of user-friendly image processing
software. This program is developing now in many countries, including the USA,
France, Germany, Sweden, Japan, Australia, and others. A network of telescopes
has been established among these countries, many of them remotely operated, as
shown in the accompanying demo. Using this feature, students in the classroom
are able to make night observations during the day, using a telescope placed in
another country. An archive of images taken on large telescopes is also
accessible, as well as resources for teachers. Students are also dealing with
real research projects, e.g. the search for asteroids, which resulted in the
discovery of a Kuiper Belt object by high-school students. Not only Hands-On
Universe gives the general public an access to professional astronomy, but it
is also a more general tool to demonstrate the use of a complex automated
system, the techniques of data processing and automation. Last but not least,
through the use of telescopes located in many countries over the globe, a form
of powerful and genuine cooperation between teachers and children from various
countries is promoted, with a clear educational goal.Comment: 4 pages, 1 figure, to appear in the proceedings of the ADASS X
conference, Boston, October 2000, ASP conf. pro
The coupling of a hearing aid loudspeaker membrane to visco-thermal air layers
Hearing aids and their components are becoming smaller. This presents new problems for the acoustical components, such as the loudspeaker. A circular membrane of a hearing aid loudspeaker is modeled in this paper. Neglecting air influences, the membrane and its suspension behave as a mass spring system. However, under operating conditions, thin layers of air on both sides of the membrane influence its behavior. Air can enter and leave these layers at certain locations on the circular edge of the layer. Since these air layers are thin, visco-thermal effects may have to be taken into account. Therefore, the air layers are not modeled by the wave equation, but by the low reduced frequency model that takes these visco-thermal effects into account. The equations of this model are solved in a polar coordinate system, using a wave-based method. The other acoustical parts of the hearing aid loudspeaker, and the membrane itself are modeled by simple lumped models. The emphasis in this paper is on the coupling of the viscothermal air layer model to the mechanical model of the membrane. Coupling of the air layer to other acoustical parts by using an impedance as boundary condition for the layer model, is also described. The resulting model is verified by experiments. The model and the measurements match reasonably well, considering the level of approximation with lumped parts
Infrared Quasi Fixed Points and Mass Predictions in the MSSM II: Large tan(beta) Scenario
We consider the infrared quasi fixed point solutions of the renormalization
group equations for the Yukawa couplings and soft supersymmetry breaking
parameters in the MSSM in the \underline{large } regime. The
existence of IR quasi fixed points together with the values of gauge couplings,
third generation quarks, lepton and Z-boson masses allows one to predict masses
of the Higgs bosons and SUSY particles as functions of the only free parameter,
, or the gluino mass. The lightest Higgs boson mass for TeV is found to be GeV for and
GeV for .Comment: 15 pages, LateX file with 4 eps figures, corrected numbers, new
column in table, last versio
The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo
Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori
class star separated by au. Observational evidence indicate a complex
environment in which each star has a circumstellar disk and drives a jet, and
the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400
au in scattered light.
Methods. We use high contrast imaging polarimetry with VLT/NaCo at and
bands.
Results. The central binary is resolved in both bands. The polarized images
show three bright and complex structures: a common dust envelope, a sharp
extended feature previously reported in direct light, and an intriguing bright
clump located 0\farcs3 south of the binary, which appears spatially connected
to the sharp extended feature.
Conclusions.We detect orbital motion when compared to previous observations,
and report a new outburst driven by the Herbig star. Our observations reveal
the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter
Very Constrained Minimal Supersymmetric Standard Models
We consider very constrained versions of the minimal supersymmetric extension
of the Standard Model (VCMSSMs) which, in addition to constraining the scalar
masses m_0 and gaugino masses m_{1/2} to be universal at some input scale,
impose relations between the trilinear and bilinear soft supersymmetry breaking
parameters A_0 and B_0. These relations may be linear, as in simple minimal
supergravity models, or nonlinear, as in the Giudice-Masiero mechanism for
generating the Higgs-mixing mu term. We discuss the application of the
electroweak vacuum conditions in VCMSSMs, which may be used to make a
prediction for tan beta as a function of m_0 and m_{1/2} that is usually
unique. We baseline the discussion of the parameter spaces allowed in VCMSSMs
by updating the parameter space allowed in the CMSSM for fixed values of tan
beta with no relation between A_0 and B_0 assumed {\it a priori}, displaying
contours of B_0 for a fixed input value of A_0, incorporating the latest CDF/D0
measurement of m_t and the latest BNL measurement of g_mu - 2. We emphasize
that phenomenological studies of the CMSSM are frequently not applicable to
specific VCMSSMs, notably those based on minimal supergravity, which require
m_0 = m_{3/2} as well as A_0 = B_0 + m_0. We then display (m_{1/2}, m_0) planes
for selected VCMSSMs, treating in a unified way the parameter regions where
either a neutralino or the gravitino is the LSP. In particular, we examine in
detail the allowed parameter space for the Giudice-Masiero model.Comment: 26 pages, 32 eps figure
Charging of single Si nanocrystals by atomic force microscopy
Conducting-tip atomic force microscopy (AFM) has been used to electronically probe silicon nanocrystals on an insulating substrate. The nanocrystal samples were produced by aerosol techniques and size classified; nanocrystal size can be controlled in the size range of 2-50 nm with a size variation of less than 10%. Using a conducting tip, the charge was injected directly into the nanocrystals, and the subsequent dissipation of the charge was monitored. Estimates of the injected charge can be made by comparison of the data with an intermittent contact mode model of the AFM response to the electrostatic force produced by the stored charge
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