3,264 research outputs found
Work hardening behavior in a steel with multiple TRIP mechanisms
Transformation induced plasticity (TRIP) behavior was studied in steel with
composition Fe-0.07C-2.85Si-15.3Mn-2.4Al-0.017N that exhibited two TRIP
mechanisms. The initial microstructure consisted of both {\epsilon}- and
{\alpha}-martensites with 27% retained austenite. TRIP behavior in the first 5%
strain was predominately austenite transforming to {\epsilon}-martensite (Stage
I), but upon saturation of Stage I, the {\epsilon}-martensite transformed to
{\alpha}-martensite (Stage II). Alloy segregation also affected the TRIP
behavior with alloy rich regions producing TRIP just prior to necking. This
behavior was explained by first principle calculations that revealed aluminum
significantly affected the stacking fault energy in Fe-Mn-Al-C steels by
decreasing the unstable stacking fault energy and promoting easy nucleation of
{\epsilon}-martensite. The addition of aluminum also raised the intrinsic
stacking fault energy and caused the {\epsilon}-martensite to be unstable and
transform to {\alpha}-martensite under further deformation. The two stage TRIP
behavior produced a high strain hardening exponent of 1.4 and led to ultimate
tensile strength of 1165 MPa and elongation to failure of 35%.Comment: submitted to Met. Mater. Trans. A manuscript E-TP-12-953-
Magnetically Mediated Transparent Conductors: InO doped with Mo
First-principles band structure investigations of the electronic, optical and
magnetic properties of Mo-doped InO reveal the vital role of magnetic
interactions in determining both the electrical conductivity and the
Burstein-Moss shift which governs optical absorption. We demonstrate the
advantages of the transition metal doping which results in smaller effective
mass, larger fundamental band gap and better overall optical transmission in
the visible -- as compared to commercial Sn-doped InO. Similar behavior
is expected upon doping with other transition metals opening up an avenue for
the family of efficient transparent conductors mediated by magnetic
interactions
Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: CF and CH
According to the Lieb's theorem the ferromagnetic interaction in
graphene-based materials with bipartite lattice is a result of disbalance
between the number of sites available for electrons in different
sublattices. Here, we report on another mechanism of the ferromagnetism in
functionalized graphene that is the direct exchange interaction between spin
orbitals. By the example of the single-side semihydrogenated (CH) and
semifluorinated (CF) graphene we show that such a coupling can partially or
even fully compensate antiferromagnetic character of indirect exchange
interactions reported earlier [Phys. Rev. B {\bf 88}, 081405(R) (2013)]. As a
result, CH is found to be a two-dimensional material with the isotropic
ferromagnetic interaction and negligibly small magnetic anisotropy, which
prevents the formation of the long-range magnetic order at finite temperature
in accordance with the Mermin-Wagner theorem. This gives a rare example of a
system where direct exchange interactions play a crucial role in determining a
magnetic structure. In turn, CF is found to be at the threshold of the
antiferromagnetic-ferromagnetic instability, which in combination with the
Dzyaloshinskii-Moriya interaction can lead to a skyrmion state.Comment: 10 page
MODELING OF SURFACE SP-SYSTEMS MAKING USE THE EXTENDED DYNAMICAL MEAN-FIELD THEORY
This work is devoted to construction of a model to describe influence of correlation and nonlocal charge interaction effects on the electronic properties of surface sp-systems on the example of Graphene adatom systems.The author likes to thank Dr. Iskakov S.N. University of Michigan, Ann Arbor, U.S.A, Dr. Krien F., Jozef Stefan Institute, Ljubljana, Slovenia, Prof. Mazurenko V.V. Ural Federal University, Yekaterinburg, Russia and Prof. Lichtenstein A.I., University of Hamburg, Hamburg, Germany
Ultrasound investigation in pregnant women with diabetes mellitus
Introduction. Ultrasound (US) has been used in obstetrics for more than 30 years and is considered to be reliable, simple, quick in results, painless and cheap method. The aim: to optimize the use of US in childbirth in pregnant women with diabetes and determine the outcome of childbirth, taking into account the condition of the fetus and newborn. Materials and methods. 52 pregnant women, among them 32 with diabetes mellitus (pre-gestational diabetes was in 20 persons and 12 persons had gestational diabetes) have been examined. The average age of pregnant women in the main group was 29.8 ± 5.4 years, in the control group - 25.7 ± 4.3 years. All women in the main and control groups were primiparous. The gestation period in the main group was 39.1 ± 0.5 weeks [38.0; 39.6], in the control group - 39.5 ± 0.7 [38.4; 40.5] weeks. Clinical-laboratory and instrumental examinations were made. Control group consisted of 20 physiologically pregnant women. To determine the condition and size of the fetus and its progress in labor, immediately at the end of the first and during the second staage of labor, transabdominal and transperineal US and Doppler examination were performed with device HD 11 XE Phillips (USA). Results. Pregnant women with diabetes are more likely to have a pathological second stage of labors due to macrosomia and problems with the birth of the fetus, as evidenced by the lack of increased angle of progress and decreased head-perineal distance. The data obtained indicate the prospects of using ultrasound in childbirth as an objective non-invasive method for predicting the likelihood of vaginal birth, which will reduce operative delivery and perinatal pathology. Conclusions. The use of ultrasound in childbirth in women with diabetes and diabetic fetopathy can determine the possibility of complications in the promotion of the fetus, including clinical narrow pelvis, shoulder dystocia, the occurrence of distress, as evidenced by the Apgar scale and CLS. Intraparietal ultrasound helps to guide the plan of childbirth, reduce the frequency of cesarean delivery, perinatal morbidity and mortality, and birth trauma
Electric field gradients in s-, p- and d-metal diborides and the effect of pressure on the band structure and T in MgB
Results of FLMTO-GGA (full-potential linear muffin-tin orbital -- generalized
gradient approximation) calculations of the band structure and boron electric
field gradients (EFG) for the new medium-T superconductor (MTSC), MgB,
and related diborides MB, M=Be, Al, Sc, Ti, V, Cr, Mo and Ta are reported.
The boron EFG variations are found to be related to specific features of their
band structure and particularly to the M-B hybridization. The strong charge
anisotropy at the B site in MgB is completely defined by the valence
electrons - a property which sets MgB apart from other diborides. The boron
EFG in MgB is weakly dependent of applied pressure: the B p electron
anisotropy increases with pressure, but it is partly compensated by the
increase of core charge assymetry. The concentration of holes in bonding
bands is found to decrease slightly from 0.067 to 0.062 holes/B under
a pressure of 10 GPa. Despite a small decrease of N(E), the Hopfield
parameter increases with pressure and we believe that the main reason for the
reduction under pressure of the superconducting transition temperature, T,
is the strong pressure dependence of phonon frequencies, which is sufficient to
compensate the electronic effects.Comment: 12 pages, 3 figure
Composition-Dependent Structural and Transport Properties of Amorphous Transparent Conducting Oxides
Structural properties of amorphous In-based oxides, In-X-O with X=Zn, Ga, Sn, or Ge, are investigated using ab initio molecular dynamics liquid-quench simulations. The results reveal that indium retains its average coordination of 5.0 upon 20% X fractional substitution for In, whereas X cations satisfy their natural coordination with oxygen atoms. This finding suggests that the carrier generation is primarily governed by In atoms, in accord with the observed carrier concentration in amorphous In-O and In-X-O. At the same time, the presence of X affects the number of six-coordinated In atoms as well as the oxygen sharing between the InO6 polyhedra. Based on the obtained interconnectivity and spatial distribution of the InO6 and XOx polyhedra in amorphous In-X-O, composition-dependent structural models of the amorphous oxides are derived. The results help explain our Hall mobility measurements in In-X-O thin films grown by pulsed-laser deposition and highlight the importance of long-range structural correlations in the formation of amorphous oxides and their transport properties
Screened-exchange Determination of the Electronic Properties of Monoclinic, Tetragonal and Cubic Zirconia
First-principles electronic band structure investigations of monoclinic, tetragonal, and cubic ZrO2 reveal the highly anisotropic nature of the conduction and valence band topologies in the monoclinic phase with electron and hole effective masses differing by over an order of magnitude in perpendicular directions. The planes of relatively high implied electron and hole mobilities intersect along a single crystallographic direction, making this the only direction readily available for exciton motion. Conversely, in the tetragonal and cubic phases, charge carrier effective masses are more isotropic and exciton motion is less restricted. These findings may explain recent experimental observations suggesting that exciton production via gamma irradiation in zirconia crystallites immersed in water is responsible for the accelerated dissociation of adsorbed water molecules on crystallite surfaces, and for the specificity of the effect to the tetragonal zirconia phase
Combining high conductivity with complete optical transparency: A band-structure approach
A comparison of the structural, optical and electronic properties of the
recently discovered transparent conducting oxide (TCO), nanoporous Ca12Al14O33,
with those of the conventional TCO's (such as Sc-doped CdO) indicates that this
material belongs conceptually to a new class of transparent conductors. For
this class of materials, we formulate criteria for the successful combination
of high electrical conductivity with complete transparency in the visible
range. Our analysis suggests that this set of requirements can be met for a
group of novel materials called electrides.Comment: 3 pages, 3 figures, submitted for publicatio
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