9,794 research outputs found
Stability of Ge-related point defects and complexes in Ge-doped SiO_2
We analyze Ge-related defects in Ge-doped SiO_2 using first-principles
density functional techniques. Ge is incorporated at the level of ~ 1 mol % and
above. The growth conditions of Ge:SiO_2 naturally set up oxygen deficiency,
with vacancy concentration increasing by a factor 10^5 over undoped SiO_2, and
O vacancies binding strongly to Ge impurities. All the centers considered
exhibit potentially EPR-active states, candidates for the identification of the
Ge(n) centers. Substitutional Ge produces an apparent gap shrinking via its
extrinsic levels.Comment: RevTeX 4 pages, 2 ps figure
Effects of a nonadiabatic wall on supersonic shock/boundary-layer interactions
Direct numerical simulations are employed to investigate a shock wave impinging on a turbulent boundary layer at free-stream Mach number M=2.28 with different wall thermal conditions, including adiabatic, cooled, and heated, for a wide range of deflection angles. It is found that the thermal boundary condition at the wall has a large effect on the size of the interaction region and on the level of pressure fluctuations. The distribution of the Stanton number shows a good agreement with prior experimental studies and confirms the strong heat transfer and complex pattern within the interaction region. An effort was also made to describe the unsteady features of the flow by means of wall pressure and heat flux spectra. Numerical results indicate that the changes in the interaction length due to the wall thermal condition are mainly linked to the incoming boundary layer, which is in agreement with previous experimental studies
Self-regulated charge transfer and band tilt in nm-scale polar GaN films
To date, the generic polarization of Bernardini, Fiorentini and Vanderbilt
(PBFV) has been widely used to address the issue of polarity in III-V nitride
semiconductors, but improvements in nitride materials and the performance of
optoelectronic devices have been limited. The current first-principles
calculation for the electronic structures of nm-scale [0001] GaN films show
that the internal electric fields and the band tilt of these films are in
opposite direction to those predicted by PBFV. Additionally, it is determined
that an intrinsic self-regulated charge transfer across the film limits the
electrostatic potential difference across the film, which renders the local
conduction band energy minimum (at the Ga-terminated surface) approximately
equal to the local valence band energy maximum (at the N-terminated surface).
This effect is found to occur in films thicker than ~4nm
PERFORMANCE AND BEHAVIOUR OF CHICKENS WITH DIFFERENT GROWING RATE REARED ACCORDING TO THE ORGANIC SYSTEM
The performance and the behaviour of three different chicken strains, reared according to the EEC-Regulation 1804/1999 organic system, were compared. The strains had very slow (Robusta maculata), slow (Kabir) and fast (Ross) growing rates, respectively. The trial was carried out on 200 chickens (male and female) per strain. Rearing lasted 81 days as
required by the EEC Regulations. At slaughter age, 20 birds per group were killed. Robusta maculata and Kabir chickens showed more intense walking activity and better foraging aptitude; their antioxidant capacity was also superior. Ross chickens had a good growth rate and feed conversion index, reaching an excellent body weight, but the mortality and the culling rate were high indicating that fast-growing strains do not adapt well to organic production. Robusta maculata showed the worst productive performance although the mortality was low and Kabir birds gave intermediate results.
The carcass traits were the best in Ross and the poorest in Robusta maculata. Male chickens were heavier and leaner than females
IGR J14257-6117, a magnetic accreting white dwarf with a very strong X-ray orbital modulation
IGR J14257-6117 is an unclassified source in the hard X-ray catalogues.
Optical follow-ups suggest it could be a Cataclysmic Variable of the magnetic
type. We present the first high S/N X-ray observation performed by \XMM\ at
0.3--10 keV, complemented with 10--80 keV coverage by \Swift/BAT, aimed at
revealing the source nature. We detected for the first time a fast periodic
variability at 509.5\,s and a longer periodic variability at 4.05\,h, ascribed
to the white dwarf (WD) spin and binary orbital periods, respectively. These
unambiguously identify IGR J14257-6117 as a magnetic CV of the Intermediate
Polar (IP) type. The energy resolved light curves at both periods reveal
amplitudes decreasing with increasing energy, with the orbital modulation
reaching in the softest band. The energy spectrum shows optically
thin thermal emission with an excess at the iron complex, absorbed by two dense
media (), partially covering the X-ray
source. These are likely localised in the magnetically confined accretion flow
above the WD surface and at the disc rim, producing the energy dependent spin
and orbital variabilities, respectively. IGR J14257-6117, joins the group of
strongest orbitally modulated IPs now counting four systems. Drawing
similarities with low-mass X-ray binaries displaying orbital dips, these IPs
should be seen at large orbital inclinations allowing azimuthally extended
absorbing material fixed in the binary frame to intercept the line of sight.
For IGR J14257-6117, we estimate (). Whether
also the mass accretion rate plays a role in the large orbital modulations in
IPs cannot be established with the present data.Comment: Accepted for publication on MNRAS. 9 pages, 6 table, 5 figure
Dependence of the drag over super hydrophobic and liquid infused surfaces on the textured surface and Weber number
Direct Numerical Simulations of a turbulent channel flow have been performed. The lower wall of the channel is made of staggered cubes with a second fluid locked in the cavities. Two viscosity ratios have been considered, m=μ1/μ2=0.02 and 0.4 (the subscript 1 indicates the fluid in the cavities and 2 the overlying fluid) mimicking the viscosity ratio in super–hydrophobic surfaces (SHS) and liquid infused surfaces (LIS) respectively. A first set of simulations with a slippery interface has been performed and results agree well with those in literature for perfect slip conditions and Stokes approximations. To assess how the dynamics of the interface affects the drag, a second set of DNS has been carried out at We=40 and 400 corresponding to We+≃10−3 and 10−2. The deformation of the interface is fully coupled to the Navier-Stokes equation and tracked in time using a Level Set Method. Two gas fractions, GF=0.5 and 0.875, have been considered to assess how the spacing between the cubes affects the deformation of the interface and therefore the drag. For the dimensions of the substrate here considered, under the ideal assumption of flat interface, staggered cubes with GF=0.875 provide about 20% drag reduction for We=0. However, a rapid degradation of the performances is observed when the dynamics of the interface is considered, and the same geometry increases the drag of about 40% with respect to a smooth wall. On the other hand, the detrimental effect of the dynamics of the interface is much weaker for GF=0.5 because of the reduced pitch between the cubes
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