50,039 research outputs found
The reflection and transmission properties of a triple band dichroic surface
The development of a triple-band dichroic surface design is detailed that is reflective in the Ka-band from 22.5 to 27.3 GHz and the Ku-band from 13.7 to 15.1 GHz, yet transparent in the S-band from 2.0 to 2.3 GHz, for all planes of incidence, and for all angles of incidence out to eta = 45 deg. The design is comprised of two gangbuster whole-surfaces separated by a distance, d, that is comparable to a fraction of a wavelength in S-band, and enhanced by the addition of a dielectric matching plate. The gangbuster array is comprised of tightly packed straight skewed dipole elements referred to as half-surfaces. Two of these half-surfaces are oriented orthogonal to each other and placed an array separation distance, s, apart to form the gangbuster whole-surface which allows any arbitrary plane of incidence. Results are given for the triple-band design with and without dielectric and conduction losses. The cross polarization properties of the dichroic surface was further investigated. It is shown that the reflection cross polarized component is dominated by the geometry of the front whole surface of the design (particularly the array separation s) and is never more than -22.5 dB in the frequency band 0 to 30 GHz. The transmission cross polarization component is dependent on both whole-surfaces and is never more than -30 dB in the same frequency band
Magnetic field induced finite size effect in type-II superconductors
We explore the occurrence of a magnetic field induced finite size effect on
the specific heat and correlation lengths of anisotropic type-II
superconductors near the zero field transition temperature Tc. Since near the
zero field transition thermal fluctuations are expected to dominate and with
increasing field strength these fluctuations become one dimensional, whereupon
the effect of fluctuations increases, it appears unavoidable to account for
thermal fluctuations. Invoking the scaling theory of critical phenomena it is
shown that the specific heat data of nearly optimally doped YBa2Cu3O7-x are
inconsistent with the traditional mean-field and lowest Landau level
predictions of a continuous superconductor to normal state transition along an
upper critical field Hc2(T). On the contrary, we observe agreement with a
magnetic field induced finite size effect, whereupon even the correlation
length longitudinal to the applied field H cannot grow beyond the limiting
magnetic length L(H). It arises because with increasing magnetic field the
density of vortex lines becomes greater, but this cannot continue indefinitely.
L(H) is then roughly set on the proximity of vortex lines by the overlapping of
their cores. Thus, the shift and the rounding of the specific heat peak in an
applied field is traced back to a magnetic field induced finite size effect in
the correlation length longitudinal to the applied field.Comment: 8 pages, 4 figure
Universal features in sequential and nonsequential two-photon double ionization of helium
We analyze two-photon double ionization of helium in both the nonsequential
and sequential regime. We show that the energy spacing between the two emitted
electrons provides the key parameter that controls both the energy and the
angular distribution and reveals the universal features present in both the
nonsequential and sequential regime. This universality, i.e., independence of
photon energy, is a manifestation of the continuity across the threshold for
sequential double ionization. For all photon energies, the energy distribution
can be described by a universal shape function that contains only the spectral
and temporal information entering second-order time-dependent perturbation
theory. Angular correlations and distributions are found to be more sensitive
to the photon energy. In particular, shake-up interferences have a large effect
on the angular distribution. Energy spectra, angular distributions
parameterized by the anisotropy parameters, and total cross sections presented
in this paper are obtained by fully correlated time-dependent ab initio
calculations.Comment: 12 pages, 8 figure
Direct Detection of Giant Close-In Planets Around the Source Stars of Caustic-Crossing Microlensing Events
We propose a direct method to detect close-in giant planets orbiting stars in
the Galactic bulge. This method uses caustic-crossing binary microlensing
events discovered by survey teams monitoring the bulge to measure light from a
planet orbiting the source star. When the planet crosses the caustic, it is
more magnified than the source star; its light is magnified by two orders of
magnitude for Jupiter size planets. If the planet is a giant close to the star,
it may be bright enough to make a significant deviation in the light curve of
the star. Detection of this deviation requires intensive monitoring of the
microlensing light curve using a 10-meter class telescope for a few hours after
the caustic. This is the only method yet proposed to directly detect close-in
planets around stars outside the solar neighborhood.Comment: 4 pages, 2 figures. Submitted to ApJ Letter
SBE13, a newly identified inhibitor of inactive polo-like kinase 1
Poster presentation at 5th German Conference on Cheminformatics: 23. CIC-Workshop Goslar, Germany. 8-10 November 2009 Protein kinases are important targets for drug development. The almost identical protein folding of kinases and the common co-substrate ATP leads to the problem of inhibitor selectivity. Type II inhibitors, targeting the inactive conformation of kinases, occupy a hydrophobic pocket with less conserved surrounding amino acids. Human polo-like kinase 1 (Plk1) represents a promising target for approaches to identify new therapeutic agents. Plk1 belongs to a family of highly conserved serine/threonine kinases, and is a key player in mitosis, where it modulates the spindle checkpoint at metaphase/anaphase transition. Plk1 is over-expressed in all today analyzed human tumors of different origin and serves as a negative prognostic marker in cancer patients. The newly identified inhibitor, SBE13, a vanillin derivative, targets Plk1 in its inactive conformation. This leads to selectivity within the Plk family and towards Aurora A. This selectivity can be explained by docking studies of SBE13 into the binding pocket of homology models of Plk1, Plk2 and Plk3 in their inactive conformation. SBE13 showed anti-proliferative effects in cancer cell lines of different origins with EC50 values between 5 microM and 39 microM and induced apoptosis. Increasing concentrations of SBE13 result in increasing amounts of cells in G2/M phase 13 hours after double thymidin block of HeLa cells. The kinase activity of Plk1 was inhibited with an IC50 of 200 pM. Taken together, we could show that carefully designed structure-based virtual screening is well-suited to identify selective type II kinase inhibitors targeting Plk1 as potential anti-cancer therapeutics
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Situating multimodal learning analytics
The digital age has introduced a host of new challenges and opportunities for the learning sciences community. These challenges and opportunities are particularly abundant in multimodal learning analytics (MMLA), a research methodology that aims to extend work from Educational Data Mining (EDM) and Learning Analytics (LA) to multimodal learning environments by treating multimodal data. Recognizing the short-term opportunities and longterm challenges will help develop proof cases and identify grand challenges that will help propel the field forward. To support the field's growth, we use this paper to describe several ways that MMLA can potentially advance learning sciences research and touch upon key challenges that researchers who utilize MMLA have encountered over the past few years
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The family drug & alcohol court (FDAC) evaluation project
This report presents the findings from the evaluation of the first pilot Family Drug and Alcohol Court (FDAC) in Britain. FDAC is a new approach to care proceedings, in cases where parental substance misuse is a key element in the local authority decision to bring proceedings. It is being piloted at the Inner London Family Proceedings Court in Wells Street. Initially the pilot was to run for three years, to the end of December 2010, but is now to continue until March 2012. The work is co-funded by the Department for Education (formerly the Department for Children, Schools and Families), the Ministry of Justice, the Home Office, the Department of Health and the three pilot authorities (Camden, Islington and Westminster). The evaluation was conducted by a research team at Brunel University, with funding from the Nuffield Foundation and the Home Office. FDAC is a specialist court for a problem that is anything but special. Its potential to help break the inter-generational cycle of harm associated with parental substance misuse goes straight to the heart of public policy and professional practice. Parental substance misuse is a formidable social problem and a key factor in around a third of long-term cases in children’s services in some areas. It is a major risk factor for child maltreatment, family separation and offending in adults, and for poor educational performance and substance misuse by children and young people. The parents’ many difficulties create serious problems for their children and place major demands on health, welfare and criminal justice services. For these reasons, parental substance misuse is a cross-cutting government agenda. FDAC is distinctive because it is a court-based family intervention which aims to improve children’s outcomes by addressing the entrenched difficulties of their parents. It has been adapted to English law and practice from a model of family treatment drug courts that is used widely in the USA and is showing promising results with a higher number of cases where parents and children were able to remain together safely, and with swifter alternative placement decisions for children if parents were unable to address their substance misuse successfully. The catalysts for the FDAC pilot were the encouraging evidence from the USA and concerns about the response to parental substance misuse through ordinary care proceedings in England: poor coordination of adult and children’s services; late interventions to protect children; delays in reaching decisions in court; and soaring costs of proceedings, linked to the cost of expert evidence.The work is co-funded by the Department for Education (formerly the Department for Children, Schools and Families), the Ministry of Justice, the Home Office, the Department of Health and the three pilot authorities (Camden, Islington and Westminster).1 The evaluation was conducted by a research team at Brunel University, with funding from the Nuffield Foundation and the Home Office
First detection of CF+ towards a high-mass protostar
We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines
of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive
protostar of the Cygnus X region. This detection occurred as part of an
unbiased spectral survey of this object in the 0.8-3 mm range, performed with
the IRAM 30m telescope. The data were analyzed using a local thermodynamical
equilibrium model (LTE model) and a population diagram in order to derive the
column density. The line velocity (-4 km s-1) and line width (1.6 km s-1)
indicate an origin from the collapsing envelope of the protostar.
We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be
a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a
total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon
ionization caused by an exterior source of UV photons suggesting that the
protostar itself is the source of ionization. Ionization from the protostellar
photosphere is not efficient enough. In contrast, X-ray ionization from the
accretion shock(s) and UV ionization from outflow shocks could provide a large
enough ionizing power to explain our CF+ detection.
Surprisingly, CF+ has been detected towards a cold, massive protostar with no
sign of an external photon dissociation region (PDR), which means that the only
possibility is the existence of a significant inner source of C+. This is an
important result that opens interesting perspectives to study the early
development of ionized regions and to approach the issue of the evolution of
the inner regions of collapsing envelopes of massive protostars. The existence
of high energy radiations early in the evolution of massive protostars also has
important implications for chemical evolution of dense collapsing gas and could
trigger peculiar chemistry and early formation of a hot core.Comment: 6 page
Implications of the isotope effects on the magnetization, magnetic torque and susceptibility
We analyze the magnetization, magnetic torque and susceptibility data of
La2-xSrxCu(16,18)O4 and YBa2(63,65)CuO7-x near Tc in terms of the universal
3D-XY scaling relations. It is shown that the isotope effect on Tc mirrors that
on the anisotropy. Invoking the generic behavior of the anisotropy the doping
dependence of the isotope effects on the critical properties, including Tc,
correlation lengths and magnetic penetration depths are traced back to a change
of the mobile carrier concentration.Comment: 5 pages, 3 figure
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