6,104 research outputs found
Spin polarization of the Ar* 2p−11/2 4s and 2p−11/2 3d resonant Auger decay
The spin-resolved Auger decay of the Ar 2p−11/2 3d state was measured at moderate energy resolution and compared with the decay of the 2p−11/2 4s. The former shows a lower transferred spin polarization and a similar, if not higher, dynamical spin polarization, supporting the statement that a fully resolved spectrum is not a necessary condition for observing dynamical spin polarization. An interpretation of the spin polarization as configuration interaction induced effect in the final ionic state leads to partial agreement with our relativistic distorted wave calculation utilizing a 36 configuration state function basis set. Comparison of the experimental and numerical results leads to ambiguities for at least one Auger line. A hypothetical, qualitative interpretation is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58121/2/b7_17_012.pd
Envelhecimento, trabalho e tempo livre: elaborando projetos de vida.
bitstream/item/71542/1/ID-30980.pd
Analysis of Optical Pulse Propagation with ABCD Matrices
We review and extend the analogies between Gaussian pulse propagation and
Gaussian beam diffraction. In addition to the well-known parallels between
pulse dispersion in optical fiber and CW beam diffraction in free space, we
review temporal lenses as a way to describe nonlinearities in the propagation
equations, and then introduce further concepts that permit the description of
pulse evolution in more complicated systems. These include the temporal
equivalent of a spherical dielectric interface, which is used by way of example
to derive design parameters used in a recent dispersion-mapped soliton
transmission experiment. Our formalism offers a quick, concise and powerful
approach to analyzing a variety of linear and nonlinear pulse propagation
phenomena in optical fibers.Comment: 10 pages, 2 figures, submitted to PRE (01/01
High On/Off Ratios in Bilayer Graphene Field Effect Transistors Realized by Surface Dopants
The unique property of bilayer graphene to show a band gap tunable by
external electrical fields enables a variety of different device concepts with
novel functionalities for electronic, optoelectronic and sensor applications.
So far the operation of bilayer graphene based field effect transistors
requires two individual gates to vary the channel's conductance and to create a
band gap. In this paper we report on a method to increase the on/off ratio in
single gated bilayer graphene field effect transistors by adsorbate doping. The
adsorbate dopants on the upper side of the graphene establish a displacement
field perpendicular to the graphene surface breaking the inversion symmetry of
the two graphene layers. Low temperature measurements indicate, that the
increased on/off ratio is caused by the opening of a mobility gap. Beside field
effect transistors the presented approach can also be employed for other
bilayer graphene based devices like photodetectors for THz to infrared
radiation, chemical sensors and in more sophisticated structures such as
antidot- or superlattices where an artificial potential landscape has to be
created.Comment: 4 pages, 4 figure
Pliocene Te Aute limestones, New Zealand: Expanding concepts for cool-water shelf carbonates
Acceptance of a spectrum of warm- through cold-water shallow-marine carbonate facies has become of fundamental importance for correctly interpreting the origin and significance of all ancient platform limestones. Among other attributes, properties that have become a hallmark for characterising many Cenozoic non-tropical occurrences include: (1) the presence of common bryozoan and epifaunal bivalve skeletons; (2) a calcite-dominated mineralogy; (3) relatively thin deposits exhibiting low rates of sediment accumulation; (4) an overall destructive early diagenetic regime; and (5) that major porosity destruction and lithification occur mainly in response to chemical compaction of calcitic skeletons during moderate to deep burial. The Pliocene Te Aute limestones are non-tropical skeletal carbonates formed at paleolatitudes near 40-42°S under the influence of commonly strong tidal flows along the margins of an actively deforming and differentially uplifting forearc basin seaway, immediately inboard of the convergent Pacific-Australian plate boundary off eastern North Island, New Zealand. This dynamic depositional and tectonic setting strongly influenced both the style and subsequent diagenetic evolution of the limestones. Some of the Te Aute limestones exhibit the above kinds of "normal" non-tropical characteristics, but others do not. For example, many are barnacle and/or bivalve dominated, and several include attributes that at least superficially resemble properties of certain tropical carbonates. In this regard, a number of the limestones are infaunal bivalve rich and dominated by an aragonite over a calcite primary mineralogy, with consequently relatively high diagenetic potential. Individual limestone units are also often rather thick (e.g., up to 50-300 m), with accumulation rates from 0.2 to 0.5 m/ka, and locally as high as 1 m/ka. Moreover, there can be a remarkable array of diagenetic features in the limestones, involving grain alteration and/or cementation to widely varying extents within any, or some combination of, the marine phreatic, burial, and meteoric diagenetic environments, including locally widespread development of meteoric cement sourced from aragonite dissolution. The message is that non-tropical shelf carbonates include a more diverse array of geological settings, of skeletal and mineralogical facies, and of diagenetic features than current sedimentary models mainly advocate. While several attributes positively distinguish tropical from non-tropical limestones, continued detailed documentation of the wide spectrum of shallow-marine carbonate deposits formed outside tropical regions remains an important challenge in carbonate sedimentology
Reinforcement-Driven Spread of Innovations and Fads
We propose kinetic models for the spread of permanent innovations and
transient fads by the mechanism of social reinforcement. Each individual can be
in one of M+1 states of awareness 0,1,2,...,M, with state M corresponding to
adopting an innovation. An individual with awareness k<M increases to k+1 by
interacting with an adopter. Starting with a single adopter, the time for an
initially unaware population of size N to adopt a permanent innovation grows as
ln(N) for M=1, and as N^{1-1/M} for M>1. The fraction of the population that
remains clueless about a transient fad after it has come and gone changes
discontinuously as a function of the fad abandonment rate lambda for M>1. The
fad dies out completely in a time that varies non-monotonically with lambda.Comment: 4 pages, 2 columns, 5 figures, revtex 4-1 format; revised version has
been expanded and put into iop format, with one figure adde
A Search for Close Binaries in the Rho Ophiuchus Star-Forming Region
We have carried out a new, near-infrared speckle imaging survey of 19 members
of the young stellar population in the nearby (d=140 pc), Rho Ophiuchi cloud
core. Results for four binary and one newly discovered triple system are
reported. Data for all known multiple systems among the pre-main-sequence
population of Rho Oph are tabulated. We define a "restricted binary fraction",
Fbr, and a "restricted companion fraction", Fcr, as counting only those systems
most detectable in the present and previous high-resolution near-infrared
imaging surveys, having separations between 0.1-1.1 arcsec and K-band magnitude
differences, Delta K < 3. Analysis of all the available multiplicity data
results in updated values of Fbr=Fcr=24%+/-11% for the Ophiuchus
pre-main-sequence population. These values are consistent with the values in
the Taurus star-forming region, and Fcr is in excess by a factor of 2 relative
to the Main Sequence at the 1-sigma level.Comment: 21 pages, 6 figures, 4 table
An Analysis of Resting-State Functional Transcranial Doppler Recordings from Middle Cerebral Arteries
Functional transcrannial Doppler (fTCD) is used for monitoring the hemodynamics characteristics of major cerebral arteries. Its resting-state characteristics are known only when considering the maximal velocity corresponding to the highest Doppler shift (so called the envelope signals). Significantly more information about the resting-state fTCD can be gained when considering the raw cerebral blood flow velocity (CBFV) recordings. In this paper, we considered simultaneously acquired envelope and raw CBFV signals. Specifically, we collected bilateral CBFV recordings from left and right middle cerebral arteries using 20 healthy subjects (10 females). The data collection lasted for 15 minutes. The subjects were asked to remain awake, stay silent, and try to remain thought-free during the data collection. Time, frequency and time-frequency features were extracted from both the raw and the envelope CBFV signals. The effects of age, sex and body-mass index were examined on the extracted features. The results showed that the raw CBFV signals had a higher frequency content, and its temporal structures were almost uncorrelated. The information-theoretic features showed that the raw recordings from left and right middle cerebral arteries had higher content of mutual information than the envelope signals. Age and body-mass index did not have statistically significant effects on the extracted features. Sex-based differences were observed in all three domains and for both, the envelope signals and the raw CBFV signals. These findings indicate that the raw CBFV signals provide valuable information about the cerebral blood flow which can be utilized in further validation of fTCD as a clinical tool. © 2013 Sejdić et al
Low temperature ellipsometry of NaV2O5
The dielectric function of alpha'NaV2O5 was measured with electric field
along the a and b axes in the photon energy range 0.8-4.5 eV for temperatures
down to 4K. We observe a pronounced decrease of the intensity of the 1 eV peak
upon increasing temperature with an activation energy of about 25meV,
indicating that a finite fraction of the rungs becomes occupied with two
electrons while others are emptied as temperature increases. No appreciable
shifts of peaks were found s in the valence state of individual V atoms at the
phase transition is very small. A remarkable inflection of this temperature
dependence at the phase transition at 34 K indicates that charge ordering is
associated with the low temperature phase.Comment: Revisions in style and order of presentation. One new figure. In
press in Physical Review B. REVTeX, 4 pages with 4 postscript figure
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