5,489 research outputs found
Investigation of lateral exciton transfer of coexistent quantum dot systems
[[abstract]]The optical characterization of the ZnCdSe/ZnSe quantum dot (QDs) system is studied by photoluminescence (PL) spectrum measured at temperatures from 22 to 300 K. The distinct quenching rates of spectral integrated intensity demonstrate that there are divergent lateral exciton transfer modes between two types of coexistent QDs with different sizes and densities. The smaller and denser QD assemblies are advantageous to trigger lateral migration of thermally activated excitons due to their shallower localization and more coupling channels. However, the carrier repopulation-induced redistribution of excitonic emission energy is contrarily observed in the deepest localized case. The extra redshift of transition energy with increasing temperature is attributed to the incompletely three-dimensional excitonic confinement induced by the morphological features. In contrast with scanning probe techniques, using PL as spectral probe is a nondestructive way to explore inner morphology of capped multiple quantum structure.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子
A Mining-Based System Framework for Deploying Knowledge Maps of Composite E-Services
Providing e-services and composite e-services on the Internet is an important trend of e-business. Composite e-services are complex processes which consist of various e-services provided by different e-service providers. In such complex environments, the flexibility and success of e-business depend on effective knowledge supports to access related information and resources of composite e-services. This work proposes a knowledge map platform to provide an effective knowledge support for utilizing composite e-services. A mining-based system framework is proposed to construct the knowledge map. Moreover, the proposed knowledge map is integrated with recommendation capability to provide users customized decision support in utilizing composite e-services
5 GHz TMRT observations of 71 pulsars
We present integrated pulse profiles at 5~GHz for 71 pulsars, including eight
millisecond pulsars (MSPs), obtained using the Shanghai Tian Ma Radio Telescope
(TMRT). Mean flux densities and pulse widths are measured. For 19 normal
pulsars and one MSP, these are the first detections at 5~GHz and for a further
19, including five MPSs, the profiles have a better signal-to-noise ratio than
previous observations. Mean flux density spectra between 400~MHz and 9~GHz are
presented for 27 pulsars and correlations of power-law spectral index are found
with characteristic age, radio pseudo-luminosity and spin-down luminosity. Mode
changing was detected in five pulsars. The separation between the main pulse
and interpulse is shown to be frequency independent for six pulsars but a
frequency dependence of the relative intensity of the main pulse and interpulse
is found. The frequency dependence of component separations is investigated for
20 pulsars and three groups are found: in seven cases the separation between
the outmost leading and trailing components decreases with frequency, roughly
in agreement with radius-to-frequency mapping; in eleven cases the separation
is nearly constant; in the remain two cases the separation between the outmost
components increases with frequency. We obtain the correlations of pulse widths
with pulsar period and estimate the core widths of 23 multi-component profiles
and conal widths of 17 multi-component profiles at 5.0~GHz using Gaussian
fitting and discuss the width-period relationship at 5~GHz compared with the
results at at 1.0~GHz and 8.6~GHz.Comment: 46 pages, 14 figures, 8 Tables, accepted by Ap
The imaginary part of the gap function in color superconductivity
We clarify general properties of the energy gap regarding its functional
dependence on the energy-momentum dictated by the invariance under a space
inversion or a time reversal. Then we derive perturbatively the equation of the
imaginary part of the gap function for dense QCD in weak coupling and
generalize our results from 2SC case to CFL case. We confirm that the imaginary
part is down by relative to the real part in weak coupling. The numerical
results show that, up to the leading order, the imaginary part is no larger
than one MeV at extremely large densities and can be as large as several MeV
the densities are of physical interest.Comment: 15 pages, 2 figures, typos corrected, a figure replaced. The version
to be appeared in Nucl.Phys.
Single crystals of LnFeAsO1-xFx (Ln=La, Pr, Nd, Sm, Gd) and Ba1-xRbxFe2As2: growth, structure and superconducting properties
A review of our investigations on single crystals of LnFeAsO1-xFx (Ln=La, Pr,
Nd, Sm, Gd) and Ba1-xRbxFe2As2 is presented. A high pressure technique has been
applied for the growth of LnFeAsO1-xFx crystals, while Ba1-xRbxFe2As2 crystals
were grown using quartz ampoule method. Single crystals were used for
electrical transport, structure, magnetic torque and spectroscopic studies.
Investigations of the crystal structure confirmed high structural perfection
and show less than full occupation of the (O, F) position in superconducting
LnFeAsO1-xFx crystals. Resistivity measurements on LnFeAsO1-xFx crystals show a
significant broadening of the transition in high magnetic fields, whereas the
resistive transition in Ba1 xRbxFe2As2 simply shifts to lower temperature.
Critical current density for both compounds is relatively high and exceeds
2x109 A/m2 at 15 K in 7 T. The anisotropy of magnetic penetration depth,
measured on LnFeAsO1-xFx crystals by torque magnetometry is temperature
dependent and apparently larger than the anisotropy of the upper critical
field. Ba1-xRbxFe2As2 crystals are electronically significantly less
anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the
existence of two energy gaps in LnFeAsO1-xFx. Scanning Tunneling Spectroscopy
reveals in addition to a superconducting gap, also some feature at high energy
(~20 meV).Comment: 27 pages, 19 figures, 2 tables, accepted to the special issue of the
Physica C on superconducting pnictide
Glutathione Peroxidase-Based Amperometric Biosensor for the Detection of S -Nitrosothiols
A new biosensor is described for the detection of S -nitrosothiols (RSNOs) based on their decomposition by immobilized glutathione peroxidase (GPx), an enzyme containing selenocysteine residue that catalytically produces nitric oxide (NO) from RSNOs. The enzyme is entrapped at the distal tip of a planar amperometric NO sensor. The new biosensor shows good sensitivity, linearity, reversibility, and response times towards various RSNO species in PBS buffer, pH 147.4 . In most cases, the response time is less than 5 14min, and the response is linear up to 6 ΜM of the tested RSNO species. The lowest detection limit is obtained for S -nitrosocysteine (CysNO), at approx. 0.2 14ΜM. The biosensor's sensitivity is not affected by the addition of EDTA as a chelating agent; an advantage over other potential catalytic enzymes that contain copper ion centers, such as CuZn-superoxide dismutase and xanthine oxidase. However, lifetime of the new sensor is limited, with sensitivity decrease of 50% after two days of use. Nonetheless, the new amperometric GPx based RSNO sensor could prove useful for detecting relative RSNO levels in biological samples, including whole blood.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55900/1/2043_ftp.pd
TMRT observations of 26 pulsars at 8.6 GHz
Integrated pulse profiles at 8.6~GHz obtained with the Shanghai Tian Ma Radio
Telescope (TMRT) are presented for a sample of 26 pulsars. Mean flux densities
and pulse width parameters of these pulsars are estimated. For eleven pulsars
these are the first high-frequency observations and for a further four, our
observations have a better signal-to-noise ratio than previous observations.
For one (PSR J0742-2822) the 8.6~GHz profiles differs from previously observed
profiles. A comparison of 19 profiles with those at other frequencies shows
that in nine cases the separation between the outmost leading and trailing
components decreases with frequency, roughly in agreement with
radius-to-frequency mapping, whereas in the other ten the separation is nearly
constant. Different spectral indices of profile components lead to the
variation of integrated pulse profile shapes with frequency. In seven pulsars
with multi-component profiles, the spectral indices of the central components
are steeper than those of the outer components. For the 12 pulsars with
multi-component profiles in the high-frequency sample, we estimate the core
width using gaussian fitting and discuss the width-period relationship.Comment: 33 pages, 49 figures, 5 Tables; accepted by Ap
An annular gap acceleration model for -ray emission of pulsars
If the binding energy of the pulsar's surface is not so high (the case of a
neutron star), both the negative and positive charges will flow out freely from
the surface of the star. The annular free flow model for -ray emission
of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of
acceleration regions (annular and core) need to be taken into account. The
annular acceleration region is defined by the magnetic field lines that cross
the null charge surface within the light cylinder. (2). If the potential drop
in the annular region of a pulsar is high enough (normally the cases of young
pulsars), charges in both the annular and the core regions could be accelerated
and produce primary gamma-rays. Secondary pairs are generated in both regions
and stream outwards to power the broadband radiations. (3). The potential drop
in the annular region grows more rapidly than that in the core region. The
annular acceleration process is a key point to produce wide emission beams as
observed. (4). The advantages of both the polar cap and outer gap models are
retained in this model. The geometric properties of the -ray emission
from the annular flow is analogous to that presented in a previous work by Qiao
et al., which match the observations well. (5). Since charges with different
signs leave the pulsar through the annular and the core regions, respectively,
the current closure problem can be partially solved.Comment: 11 pages 2 figures, accepted by Chinese Journal of Astronomy and
Astrophysic
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