5,546 research outputs found
Detection of Massive Forming Galaxies at Redshifts Greater than One
The complex problem of when and how galaxies formed has not until recently
been susceptible of direct attack. It has been known for some time that the
excessive number of blue galaxies counted at faint magnitudes implies that a
considerable fraction of the massive star formation in the universe occurred at
z < 3, but, surprisingly, spectroscopic studies of galaxies down to a B
magnitude of 24 found little sign of the expected high-z progenitors of current
massive galaxies, but rather, in large part, small blue galaxies at modest
redshifts z \sim 0.3. This unexpected population has diverted attention from
the possibility that early massive star-forming galaxies might also be found in
the faint blue excess. From KECK spectroscopic observations deep enough to
encompass a large population of z > 1 field galaxies, we can now show directly
that in fact these forming galaxies are present in substantial numbers at B
\sim 24, and that the era from redshifts 1 to 2 was clearly a major period of
galaxy formation. These z > 1 galaxies have very unusual morphologies as seen
in deep HST WFPC2 images.Comment: 10 pages LaTeX + 5 PostScript figures in uuencoded gzipped tar file;
aasms4.sty, flushrt.sty, overcite.sty (the two aastex4.0 and overcite.sty
macros are available from xxx.lanl.gov) Also available (along with style
files) via anonymous ftp to ftp://hubble.ifa.hawaii.edu/pub/preprints .
E-print version of paper adds citation cross-references to other archived
e-prints, where available. To appear in Nature October 19, 199
Detection of Lyman-alpha Emitting Galaxies at Redshift z=4.55
Studies of the formation and early history of galaxies have been hampered by
the difficulties inherent in detecting faint galaxy populations at high
redshift. As a consequence, observations at the highest redshifts (3.5 < z < 5)
have been restricted to objects that are intrinsically bright. These include
quasars, radio galaxies, and some Ly alpha-emitting objects that are very close
to (within ~10 kpc) -- and appear to be physically associated with -- quasars.
But the extremely energetic processes which make these objects easy to detect
also make them unrepresentative of normal (field) galaxies. Here we report the
discovery using Keck spectroscopic observations of two Ly alpha-emitting
galaxies at redshift z = 4.55, which are sufficiently far from the nearest
quasar (~700 kpc) that radiation from the quasar is unlikely to provide the
excitation source of the Ly alpha emission. Instead, these galaxies appear to
be undergoing their first burst of star formation, at a time when the Universe
was less than one billion years old.Comment: 8 pages, 1 landscape table, and 3 PostScript figures. Uses
aaspp4.sty, flushrt.sty, aj_pt4.sty, overcite.sty (style macros available
from xxx.lanl.gov) Figure 1 is bitmapped to 100 dpi. The original PostScript
version of Fig. 1 is available via anonymous ftp to
ftp://hubble.ifa.hawaii.edu/pub/preprints To appear in Natur
Rice protein radicals: growth and stability under microwave treatment
published_or_final_versio
Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging
We have studied the effect of ageing within the miscibility gap on the
electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler
Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a
-based (-phase) towards a close-packed structure (-phase).
Negative magnetoresistance which shows an almost linear dependence on the
square of magnetization with different slopes in the - and -phases,
was observed. This magnetoresistive effect has been associated with the
existence of Mn-rich clusters with the CuAlMn-structure. The effect of an
applied magnetic field on the martensitic transition has also been studied. The
entropy change between the - and -phases shows negligible dependence
on the magnetic field but it decreases significantly with annealing time within
the miscibility gap. Such a decrease is due to the increasing amount of
CuMnAl-rich domains that do not transform martensitically.Comment: 9 pages, 9 figures, accepted for publication in PR
Capacity and Procedural Accounts of Impaired Memory in Depression
Findings of impaired memory in states of dysphoria or depression are summarized and subsumed under different accounts of mood-related memory deficits. Theoretical accounts based on the assumption of a storage system of limited capacity are compared to accounts which emphasize the role of procedures and strategies in attending and remembering. Two reanalyses of a recent experiment in the process-dissociation paradigm are reported. They address issues of dysphoria-related differences in automatic versus controlled uses of memory in a task of word-stem completion. The two reanalyses rest on different assumptions about the relation between automatic and controlled components, but they converge in highlighting the advantages of a procedural rather than capacity-based view of memory deficits. finally. similarities to other research domains and theoretical approaches are outlined
Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring
The effects of electron-electron interaction of a two-electron nanoring on
the energy levels and far-infrared (FIR) spectroscopy have been investigated
based on a model calculation which is performed within the exactly numerical
diagonalization. It is found that the interaction changes the energy spectra
dramatically, and also shows significant influence on the FIR spectroscopy. The
crossings between the lowest spin-singlet and triplet states induced by the
coulomb interaction are clearly revealed. Our results are related to the
experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223
(2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15
Improving megasite management performance through incentives : lessons learned from the Shanghai Expo Construction
Author name used in this manuscript: Carol H. K. Hon2012-2013 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe
Sacrificial-template-free synthesis of core-shell C@Bi2S3 heterostructures for efficient supercapacitor and H-2 production applications
Core-shell heterostructures have attracted considerable attention owing to their unique properties and broad range of applications in lithium ion batteries, supercapacitors, and catalysis. Conversely, the effective synthesis of Bi2S3 nanorod core@ amorphous carbon shell heterostructure remains an important challenge. In this study, C@Bi2S3 core-shell heterostructures with enhanced supercapacitor performance were synthesized via sacrificial-template-free one-pot-synthesis method. The highest specific capacities of the C@Bi2S3 core shell was 333.43 F g(-1) at a current density of 1 A g(-1). Core-shell-structured C@Bi2S3 exhibits 1.86 times higher photocatalytic H-2 production than the pristine Bi2S3 under simulated solar light irradiation. This core-shell feature of C@Bi2S3 provides efficient charge separation and transfer owing to the formed heterojunction and a short radial transfer path, thus efficiently diminishing the charge recombination; it also facilitates plenty of active sites for the hydrogen evolution reaction owing to its mesoporous nature. These outcomes will open opportunities for developing low-cost and noble-metal-free efficient electrode materials for water splitting and supercapacitor applications
Protein Pattern Formation
Protein pattern formation is essential for the spatial organization of many
intracellular processes like cell division, flagellum positioning, and
chemotaxis. A prominent example of intracellular patterns are the oscillatory
pole-to-pole oscillations of Min proteins in \textit{E. coli} whose biological
function is to ensure precise cell division. Cell polarization, a prerequisite
for processes such as stem cell differentiation and cell polarity in yeast, is
also mediated by a diffusion-reaction process. More generally, these functional
modules of cells serve as model systems for self-organization, one of the core
principles of life. Under which conditions spatio-temporal patterns emerge, and
how these patterns are regulated by biochemical and geometrical factors are
major aspects of current research. Here we review recent theoretical and
experimental advances in the field of intracellular pattern formation, focusing
on general design principles and fundamental physical mechanisms.Comment: 17 pages, 14 figures, review articl
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