67,820 research outputs found
Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser
A method to achieve high-brightness self-amplified spontaneous emission (HB-SASE) in the free-electron laser (FEL) is described. The method uses repeated nonequal electron beam delays to delocalize the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated, using linear theory and numerical simulations, that the radiation coherence length can be increased by approximately 2 orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft x-ray and near transform-limited pulses in the hard x-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research
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Normative Values for 18-30 Ages of Benton Visual Retention Test Correct Scores and Intelligence Quotients: A Short Report for Clinical Comparison
The Benton Visual Retention Test (BVRT) is a well known test used to assess visual memory deficits and visual spatial abilities in patients. There is normative data available for the 18-30 age range though it is not comprehensive and does not cover the higher intelligence quotient ranges. Findings from two studies are presented in combination for use as normative correct score values
Towards Zeptosecond-Scale Pulses from X-Ray Free-Electron Lasers
The short wavelength and high peak power of the present generation of
free-electron lasers (FELs) opens the possibility of ultra-short pulses even
surpassing the present (tens to hundreds of attoseconds) capabilities of other
light sources - but only if x-ray FELs can be made to generate pulses
consisting of just a few optical cycles. For hard x-ray operation (~0.1nm),
this corresponds to durations of approximately a single attosecond, and below
into the zeptosecond scale. This talk will describe a novel method to generate
trains of few-cycle pulses, at GW peak powers, from existing x-ray FEL
facilities by using a relatively short 'afterburner'. Such pulses would enhance
research opportunity in atomic dynamics and push capability towards the
investigation of electronic-nuclear and nuclear dynamics. The corresponding
multi-colour spectral output, with a bandwidth envelope increased by up to two
orders of magnitudes over SASE, also has potential applications.Comment: Submitted to 35th International Free Electron Laser Conference, New
York, 201
Rate effects on layering of a confined linear alkane
We perform drainage experiments of a linear alkane fluid (n-hexadecane) down
to molecular thicknesses, and focus on the role played by the confinement rate.
We show that molecular layering is strongly influenced by the velocity at which
the confining walls are approached: under high enough shear rates, the confined
medium behaves as a structureless liquid of enhanced viscosity for film
thickness below 10 nm. Our results also lead us to conclude that a
rapidly confined film can be quenched in a metastable disordered state, which
might be related with recent intriguing results on the shear properties of
confined films produced at different rates [Zhu and Granick, Phys. Rev. Lett.
{\bf 93}, 096101 (2004)]
High Redshift Candidates and the Nature of Small Galaxies in the Hubble Deep Field
We present results on two related topics: 1. A discussion of high redshift
candidates (z>4.5), and 2. A study of very small galaxies at intermediate
redshifts, both sets being detected in the region of the northern Hubble Deep
Field covered by deep NICMOS observations at 1.6 and 1.1 microns. The high
redshift candidates are just those with redshift z>4.5 as given in the recent
catalog of Thompson, Weymann and Storrie-Lombardi, while the ``small galaxy''
sample is defined to be those objects with isophotal area <= 0.2 squ. arcsec
and with photometric redshifts 1<z<4.5. Of the 19 possible high redshift
candidates listed in the Thompson et al. catalog, 11 have (nominal) photometric
redshifts less than 5.0. Of these, however, only 4 are ``robust'' in the sense
of yielding high redshifts when the fluxes are randomly perturbed with errors
comparable to the estimated measuring error in each wave band. For the 8 other
objects with nominal photometric redshifts greater than 5.0, one (WFPC2 4--473)
has a published spectroscopic redshift. Of the remaining 7, 4 are robust in the
sense indicated above. Two of these form a close pair (NIC 586 and NIC 107).
The redshift of the object having formally the highest redshift, at 6.56
(NIC118 = WFPC2 4--601), is problematic, since F606W and F814W flux are clearly
present, and the nature of this object poses a dilemma. (abridged)Comment: 44 pages, 12 figures, to appear in ApJ v591, July 10, 200
Spinor Dynamics-Driven Formation of a Dual-Beam Atom Laser
We demonstrate a novel dual-beam atom laser formed by outcoupling oppositely
polarized components of an F=1 spinor Bose-Einstein condensate whose Zeeman
sublevel populations have been coherently evolved through spin dynamics. The
condensate is formed through all-optical means using a single-beam running-wave
dipole trap. We create a condensate in the field-insensitive state, and
drive coherent spin-mixing evolution through adiabatic compression of the
initially weak trap. Such dual beams, number-correlated through the angular
momentum-conserving reaction , have been
proposed as tools to explore entanglement and squeezing in Bose-Einstein
condensates, and have potential use in precision phase measurements.Comment: 4 pages, 4 figure
zCOSMOS: A large VLT/VIMOS redshift survey covering 0 < z < 3 in the COSMOS field
zCOSMOS is a large-redshift survey that is being undertaken in the COSMOS field using 600 hr of observation
with the VIMOS spectrograph on the 8 m VLT. The survey is designed to characterize the environments of COSMOS
galaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic
information on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (1) zCOSMOSbright,
a magnitude-limited I-band I_(AB) < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole
1.7 deg^2 COSMOS ACS field, for which the survey parameters at z ~ 0.7 are designed to be directly comparable to
those of the 2dFGRS at z ~ 0.1; and (2) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through
color-selection criteria to have 1.4 < z < 3.0, within the central 1 deg^2. This paper describes the survey design and the
construction of the target catalogs and briefly outlines the observational program and the data pipeline. In the first
observing season, spectra of 1303 zCOSMOS-bright targets and 977 zCOSMOS-deep targets have been obtained.
These are briefly analyzed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly
zCOSMOS-bright, when it is finally completed between 2008 and 2009. The power of combining spectroscopic and
photometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in
determining which of the less reliable spectroscopic redshifts are correct and which are incorrect. These techniques
bring the overall success rate in the zCOSMOS-bright so far to almost 90% and to above 97% in the 0.5 < z < 0.8
redshift range. Our zCOSMOS-deep spectra demonstrate the power of our selection techniques to isolate high-redshift
galaxies at 1.4 < z < 3.0 and of VIMOS to measure their redshifts using ultraviolet absorption lines
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