8,159 research outputs found
Formation of a reliable intermediate band in Si heavily coimplanted with chalcogens (S, Se, Te) and group III elements (B, Al)
This first-principles study describes the properties of Si implanted with several chalcogen species (S, Se, Te) at doses considerably above the equilibrium solubility limit, especially when coimplanted with the group III atoms B and Al. The measurements of chalcogen-implanted Si show strong optical absorption in the infrared range. The calculations carried out show that substitution of Si by chalcogen atoms requires lower formation energy than the interstitial implantation. In the resulting electronic structure, at concentrations close to 0.5%, an impurity band determined by the properties of the chalcogens introduced is observed in the forbidden energy gap of Si. Although this band is a few tenths of an electron volt wide, it remains energetically isolated from both the valence and the conduction bands. Appropriate coimplantation with group III elements allows control over the occupation of the intermediate band while modifying its energies only slightly. A moderate energy gain (especially small for B) seems to be obtained when p-doping atoms occupy the sites next to those of the chalcogens. Therefore, the apparent electrostatic attraction between species that in isolation would act as acceptors and double donors is smaller than expected. The intermediate-band properties have been preserved for all of the coimplanted compounds analyzed here, regardless of the species involved or the distance between them, which constitutes an appreciable advantage for the design of new experimental materials
Hyperuniform long-range correlations are a signature of disordered jammed hard-particle packings
We show that quasi-long-range (QLR) pair correlations that decay
asymptotically with scaling in -dimensional Euclidean space
, trademarks of certain quantum systems and cosmological
structures, are a universal signature of maximally random jammed (MRJ)
hard-particle packings. We introduce a novel hyperuniformity descriptor in MRJ
packings by studying local-volume-fraction fluctuations and show that
infinite-wavelength fluctuations vanish even for packings with size- and
shape-distributions. Special void statistics induce hyperuniformity and QLR
pair correlations.Comment: 10 pages, 3 figures; changes to figures and text based on review
process; accepted for publication at Phys. Rev. Let
TDDFT predictions of UV-vis spectra in ethanol for an array of curcumin analogues
The time-dependent density functional theory (TDDFT) approach has been utilized to predict UV-visible absorption spectra for an assortment of curcuminoids - analogues of the turmeric extract, curcumin. Curcumin\u27s UV-vis spectrum was modeled using the B3LYP, CAM=B3LYP, PBE0 and LC-BLYP density functionals. All methods utilized the 6–311++G** basis set for all atoms. Experimentally obtained UV-vis spectra were collected for all curcuminoids in ethanol, thus all spectra were modeled with implicit solvent effects using the conductor-like polarizable continuum model (C-PCM). The quality of spectral matching for the various density functionals are presented as are the predictive strengths of TDDFT in general for UV-vis spectra for this class of compounds
Efficient feedback controllers for continuous-time quantum error correction
We present an efficient approach to continuous-time quantum error correction
that extends the low-dimensional quantum filtering methodology developed by van
Handel and Mabuchi [quant-ph/0511221 (2005)] to include error recovery
operations in the form of real-time quantum feedback. We expect this paradigm
to be useful for systems in which error recovery operations cannot be applied
instantaneously. While we could not find an exact low-dimensional filter that
combined both continuous syndrome measurement and a feedback Hamiltonian
appropriate for error recovery, we developed an approximate reduced-dimensional
model to do so. Simulations of the five-qubit code subjected to the symmetric
depolarizing channel suggests that error correction based on our approximate
filter performs essentially identically to correction based on an exact quantum
dynamical model
Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. I. Polydisperse spheres
Hyperuniform many-particle distributions possess a local number variance that
grows more slowly than the volume of an observation window, implying that the
local density is effectively homogeneous beyond a few characteristic length
scales. Previous work on maximally random strictly jammed sphere packings in
three dimensions has shown that these systems are hyperuniform and possess
unusual quasi-long-range pair correlations, resulting in anomalous logarithmic
growth in the number variance. However, recent work on maximally random jammed
sphere packings with a size distribution has suggested that such
quasi-long-range correlations and hyperuniformity are not universal among
jammed hard-particle systems. In this paper we show that such systems are
indeed hyperuniform with signature quasi-long-range correlations by
characterizing the more general local-volume-fraction fluctuations. We argue
that the regularity of the void space induced by the constraints of saturation
and strict jamming overcomes the local inhomogeneity of the disk centers to
induce hyperuniformity in the medium with a linear small-wavenumber nonanalytic
behavior in the spectral density, resulting in quasi-long-range spatial
correlations. A numerical and analytical analysis of the pore-size distribution
for a binary MRJ system in addition to a local characterization of the
n-particle loops governing the void space surrounding the inclusions is
presented in support of our argument. This paper is the first part of a series
of two papers considering the relationships among hyperuniformity, jamming, and
regularity of the void space in hard-particle packings.Comment: 40 pages, 15 figure
Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br and CF3I
Using synchrotron radiation negative ions have been detected by mass spectrometry following vacuum-UV photoexcitation of trifluorochloromethane (CFCl), trifluorobromomethane (CFBr) and trifluoroiodomethane (CFI). The anions F, X, F, FX, CF, CF and CF were observed from all three molecules, where X = Cl, Br or I, and their ion yields recorded in the range 8-35 eV. With the exception of Br and I, the anions observed show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Dissociative electron attachment, following photoionization of CFBr and CFI as the source of low-energy electrons, is shown to dominate the observed Br and I signals, respectively. Cross sections for ion-pair formation are put on to an absolute scale by calibrating the signal strengths with those of F from both SF and CF. These anion cross sections are normalized to vacuum-UV absorption cross sections, where available, and the resulting quantum yields are reported. Anion appearance energies are used to calculate upper limits to 298 K bond dissociation energies for (CF-X) which are consistent with literature values. We report new data for (CFI-F) ≤ 2.7 ± 0.2 eV and (CFI) ≤ (598 ± 22) kJ mol. No ion-pair formation is observed below the ionization energy of the parent molecule for CFCl and CFBr, and only weak signals (in both I and F) are detected for CFI. These observations suggest neutral photodissociation is the dominant exit channel to Rydberg state photoexcitation at these lower energies
Lunar particle shadows and boundary layer experiment: Plasma and energetic particles on the Apollo 15 and 16 subsatellites
The lunar particle shadows and boundary layer experiments aboard the Apollo 15 and 16 subsatellites and scientific reduction and analysis of the data to date are discussed with emphasis on four major topics: solar particles; interplanetry particle phenomena; lunar interactions; and topology and dynamics of the magnetosphere at lunar orbit. The studies of solar and interplanetary particles concentrated on the low energy region which was essentially unexplored, and the studies of lunar interaction pointed up the transition from single particle to plasma characteristics. The analysis concentrated on the electron angular distributions as highly sensitive indicators of localized magnetization of the lunar surface. Magnetosphere experiments provided the first electric field measurements in the distant magnetotail, as well as comprehensive low energy particle measurements at lunar distance
- …