822 research outputs found
Correcting for the Effects of Interstellar Extinction
This paper addresses the issue of how best to correct astronomical data for
the wavelength-dependent effects of Galactic interstellar extinction. The main
general features of extinction from the IR through the UV are reviewed, along
with the nature of observed spatial variations. The enormous range of
extinction properties found in the Galaxy, particularly in the UV spectral
region, is illustrated. Fortunately, there are some tight constraints on the
wavelength dependence of extinction and some general correlations between
extinction curve shape and interstellar environment. These relationships
provide some guidance for correcting data for the effects of extinction.
Several strategies for dereddening are discussed along with estimates of the
uncertainties inherent in each method. In the Appendix, a new derivation of the
wavelength dependence of an average Galactic extinction curve from the IR
through the UV is presented, along with a new estimate of how this extinction
law varies with the parameter R = A(V)/E(B-V). These curves represent the true
monochromatic wavelength dependence of extinction and, as such, are suitable
for dereddening IR--UV spectrophotometric data of any resolution, and can be
used to derive extinction relations for any photometry system.Comment: To appear in PASP (January 1999) 14 pages including 4 pages of
figures Uses emulateapj style. PASP, in press (January 1999
A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region
The coincidence cross-section and the interference structure function, R_LT,
were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and
central momentum transfer of q=400 MeV/c. The measurement was at an opening
angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to
65 MeV. The R_LT structure function is found to be consistent with zero for E_m
> 50 MeV, confirming an earlier study which indicated that R_L vanishes in this
region. The integrated strengths of the p- and s-shell are compared with a
Distorted Wave Impulse Approximation calculation. The s-shell strength and
shape are compared with a Hartree Fock-Random Phase Approximation calculation.
The DWIA calculation overestimates the cross sections for p- and s-shell proton
knockout as expected, but surprisingly agrees with the extracted R_LT value for
both shells. The HF-RPA calculation describes the data more consistently, which
may be due to the inclusion of 2-body currents in this calculation.Comment: 8 Pages LaTex, 5 postscript figures. Submitted to Phys. Rev.
Quasielastic 12C(e,e'p) Reaction at High Momentum Transfer
We measured the 12C(e,e'p) cross section as a function of missing energy in
parallel kinematics for (q,w) = (970 MeV/c, 330 MeV) and (990 MeV/c, 475 MeV).
At w=475 MeV, at the maximum of the quasielastic peak, there is a large
continuum (E_m > 50 MeV) cross section extending out to the deepest missing
energy measured, amounting to almost 50% of the measured cross section. The
ratio of data to DWIA calculation is 0.4 for both the p- and s-shells. At w=330
MeV, well below the maximum of the quasielastic peak, the continuum cross
section is much smaller and the ratio of data to DWIA calculation is 0.85 for
the p-shell and 1.0 for the s-shell. We infer that one or more mechanisms that
increase with transform some of the single-nucleon-knockout into
multinucleon knockout, decreasing the valence knockout cross section and
increasing the continuum cross section.Comment: 14 pages, 7 figures, Revtex (multicol, prc and aps styles), to appear
in Phys Rev
Bodily relations and reciprocity in the art of Sonia Khurana
This article explores the significance of the ‘somatic’ and ‘ontological turn’ in locating the radical politics articulated in the contemporary performance, installation, video and digital art practices of New Delhi-based artist, Sonia Khurana (b. 1968). Since the late 1990s Khurana has fashioned a range of artworks that require new sorts of reciprocal and embodied relations with their viewers. While this line of art practice suggests the need for a primarily philosophical mode of inquiry into an art of the body, such affective relations need to be historicised also in relation to a discursive field of ‘difference’ and public expectations about the artist’s ethnic, gendered and national identity. Thus, this intimate, visceral and emotional field of inter- and intra-action is a novel contribution to recent transdisciplinary perspectives on the gendered, social and sentient body, that in turn prompts a wider debate on the ethics of cultural commentary and art historiography
The Far-Infrared Properties of Spatially Resolved AKARI Observations
We present the spatially resolved observations of IRAS sources from the
Japanese infrared astronomy satellite AKARI All-Sky Survey during the
performance verification (PV) phase of the mission. We extracted reliable point
sources matched with IRAS point source catalogue. By comparing IRAS and AKARI
fluxes, we found that the flux measurements of some IRAS sources could have
been over or underestimated and affected by the local background rather than
the global background. We also found possible candidates for new AKARI sources
and confirmed that AKARI observations resolved IRAS sources into multiple
sources. All-Sky Survey observations are expected to verify the accuracies of
IRAS flux measurements and to find new extragalactic point sources.Comment: 11 pages, 7 figures, accepted publication in PASJ AKARI special issu
HITRAP: A facility at GSI for highly charged ions
An overview and status report of the new trapping facility for highly charged
ions at the Gesellschaft fuer Schwerionenforschung is presented. The
construction of this facility started in 2005 and is expected to be completed
in 2008. Once operational, highly charged ions will be loaded from the
experimental storage ring ESR into the HITRAP facility, where they are
decelerated and cooled. The kinetic energy of the initially fast ions is
reduced by more than fourteen orders of magnitude and their thermal energy is
cooled to cryogenic temperatures. The cold ions are then delivered to a broad
range of atomic physics experiments.Comment: 8 pages, 11 figure
Investigation of the Exclusive 3He(e,e'pp)n Reaction
Cross sections for the 3He(e,e'pp)n reaction were measured over a wide range
of energy and three- momentum transfer. At a momentum transfer q=375 MeV/c,
data were taken at transferred energies omega ranging from 170 to 290 MeV. At
omega=220 MeV, measurements were performed at three q values (305, 375, and 445
MeV/c). The results are presented as a function of the neutron momentum in the
final-state, as a function of the energy and momentum transfer, and as a
function of the relative momentum of the two-proton system. The data at neutron
momenta below 100 MeV/c, obtained for two values of the momentum transfer at
omega=220 MeV, are well described by the results of continuum-Faddeev
calculations. These calculations indicate that the cross section in this domain
is dominated by direct two-proton emission induced by a one-body hadronic
current. Cross section distributions determined as a function of the relative
momentum of the two protons are fairly well reproduced by continuum-Faddeev
calculations based on various realistic nucleon-nucleon potential models. At
higher neutron momentum and at higher energy transfer, deviations between data
and calculations are observed that may be due to contributions of isobar
currents.Comment: 14 pages, 1 table, 17 figure
Деформационное упрочнение начально-изотропных металлов при деформировании по траекториям малой кривизны
На примере стали мартенситного класса исследованы закономерности деформационного
упрочнения при нагружении по траекториям, имеющим вид двухзвенных ломаных, которым
соответствуют траектории деформирования малой кривизны. Показано, что поверхность
нагружения, разделяющая области упругого и упругопластического деформирования, смещается
в направлении вектора, который соединяет центр поверхности нагружения и изображающую
точку на траектории нагружения, при этом не изменяется форма ее фронтальной
части. Зависимость величины смещения центра поверхности нагружения от
интенсивности накопленных пластических деформаций описывается кривой, инвариантной
к виду траектории нагружения.На прикладі сталі мартенситного класу досліджено закономірності деформаційного
зміцнення при навантаженні по траєкторіях, що мають вигляд
дволанкових ламаних, яким відповідають траєкторії деформування малої
кривини. Показано, що поверхня навантаження, яка розділяє області пружного
та пружнопластичного деформування, зміщується у напрямку вектора,
який з ’єднує центр поверхні навантаження та відображуючу точку на траєкторії
навантаження, при цьому форма фронтальної частини не змінюється.
Залежність величини зміщення центра поверхні навантаження від інтенсивності
накопичених пластичних деформацій описується кривою, яка є інваріантною
відносно траєкторії навантаження.By the example of martensitic steel we study
regularities of strain hardening under loading
along two-section broken lines corresponding
to slightly curved strain paths. It is shown that
the loading surface separating domains of elastic
and elastoplastic strains (yield surface) is
displaced in the direction of a vector connecting
the surface center with the loading trajectory
image point, while the shape of its frontal
part remains unchanged. The yield surface center
displacement versus the intensity of accumulated
plastic strains is described by a curve
invariant to the loading trajectory
Designing electronic collaborative learning environments
Electronic collaborative learning environments for learning and working are in vogue. Designers design them according to their own constructivist interpretations of what collaborative learning is and what it should achieve. Educators employ them with different educational approaches and in diverse situations to achieve different ends. Students use them, sometimes very enthusiastically, but often in a perfunctory way. Finally, researchers study them and—as is usually the case when apples and oranges are compared—find no conclusive evidence as to whether or not they work, where they do or do not work, when they do or do not work and, most importantly, why, they do or do not work. This contribution presents an affordance framework for such collaborative learning environments; an interaction design procedure for designing, developing, and implementing them; and an educational affordance approach to the use of tasks in those environments. It also presents the results of three projects dealing with these three issues
A model for two-proton emission induced by electron scattering
A model to study two-proton emission processes induced by electron scattering
is developed. The process is induced by one-body electromagnetic operators
acting together with short-range correlations, and by two-body
currents. The model includes all the diagrams containing a single correlation
function. A test of the sensitivity of the model to the various theoretical
inputs is done. An investigation of the relevance of the currents is
done by changing the final state angular momentum, excitation energy and
momentum transfer. The sensitivity of the cross section to the details of the
correlation function is studied by using realistic and schematic correlations.
Results for C, O and Ca nuclei are presented.Comment: 30 pages, 18 figures, 3 table
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