476 research outputs found
Anisotropy of the in-plane angular magnetoresistance of electron-doed Sr1-xLaxCuO2 thin films
Signatures of antiferromagnetism (AF) in the underdoped Ln2-xCexCuO4 (Ln =
Nd, Pr,...) family are observed even for doping levels for which
superconductivity exists. We have looked for a similar property in a different
electron-doped cuprate family, Sr1-xLaxCuO2, which consists of CuO2 planes
separated by Sr/La atoms, and is exempt of the possible influence of magnetic
rare earth ions. We report in-plane magnetoresistance measurements in the
normal state of underdoped, superconducting, c-axis oriented, epitaxial
Sr1-xLaxCuO2 thin films. This probe is sensitive to spin arrangement and we
find that the in-plane magnetoresistance, which is negative and does not
saturate for T, exhibits an angular dependence when measured upon rotating a
magnetic field within the CuO2 planes. The analysis reveals a superposition of
fourfold and twofold angular oscillations. Both of these increase in amplitude
with increasing field and decreasing and appear below a temperature, which gets
higher with decreasing doping levels. Our results demonstrate that these
magnetoresistance oscillations, also observed for the Ln2-xCexCuO4 (Ln = Nd,
Pr,...) family and attributed to an AF signature, are, without ambiguity, a
property of CuO2 planes. Besides, these oscillations vary with doping in an
unusual way compared to previous results: fourfold oscillations are essentially
present in the more underdoped samples while only twofold oscillations are
visible in the less underdoped ones. This intriguing observation appears to be
a consequence of spin dilution with increasing doping level.Comment: 25 pages, 6 figure
Cross sections and transport properties of negative ions in rare gases
We have used a combination of a simple semi-analytic theory - Momentum Transfer Theory (MTT) and exact Monte Carlo (MC) simulations to develop momentum transfer cross sections of negative ions in collisions with noble gases based on the available data for reduced mobility at 300K as a function of E/N. At very low energies, we extrapolated obtained cross sections using Langevin's cross section and supplemented it by the total detachment cross section that was used from the threshold around 6 eV up to 100 eV. Other possible reactive processes have not been taken into account. A good agreement for the mean energy and diffusion coefficients is an independent proof of the validity of the cross sections that were derived for the negative ion mobility data
Design and simulation of InGaAs/AlAsSb quantum-cascade lasers for short wavelength emission
The design and simulation of an In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade laser emitting in the near infrared is presented. Designed using a self-consistent rate equation solver coupled with an energy balance rate equation, the proposed laser has a calculated population inversion of ~20% at 77 K and sufficient gain to achieve room-temperature laser emission at Ī» ~2.8 Āµm. Threshold currents in the range 4ā8 kA/cm2 are estimated as the temperature increases from 77 K to 300 K. The output characteristics of the proposed laser are compared to an existing Ī» ~3.1 Āµm In-0.53Ga-0.47As/Al-0.56As-0.44Sb quantum-cascade structure presented in the literature
The influence of antero-posterior dentoskeletal pattern on the value of nasal soft tissue angles: a cephalometric study
Background: The aim of this study was to examine the influence of sagittal dentoskeletal pattern on the value of profile nasal soft tissue angles and estimate the significance of examined differences for each angle.Materials and methods: Lateral cephalograms were used to examine the nasofrontal angle, nasofacial angle, nasal tip angle, and nasolabial angle of 120 adult Caucasian subjects (60 male and 60 female) from the central Balkan area. Subjects were divided into four groups according to the ANB angle and incisors inclination: class I as the control group, class II division 1, class II division 2 and class III.Results: By evaluating the influence of sagittal dentoskeletal relationships on the values of examined angles, significant differences were found among subjects with class I and class II/2 (p = 0.028), so as class III (p = 0.002) for nasal tip angle. The nasofacial angle was found to differ among subjects with class I and class II/1 (p = 0.002), so as class III (p = 0.001).Conclusions: Different dentoskeletal patterns have significant influence on values of the nasal tip angle and nasofacial angle, and donāt have influence on the values of the nasofrontal and nasolabial angle
Inheritance of flower type in some grape varieties (Vitis vinifera L.)
This paper presents the results and genetical analysis of crossing grape varieties Vitis vinifera L. with regard to the inheritance of flower type. From the results obtained, following conclusions could be drawn:The flower type (hermaphrodite and female) in grape varieties Vitis vinifera L. is controlled by two allels. The genetic factor for female flower is designated by sr and the factor for hermaphroditism by Sh. FactorĀ Sf is recessive to Sh.Varieties with hermap hrodite flower type are either homozygous (Sh Sh) or heterozygous (Sh Sf) for hermaphroditism. Out of 20 tested varieUes with hermaphrodite flowers, 14 were heterozygous and 6 homozygous. The following varieties are homozygous: Datier, Smederevka, Queen of the Vineyards, Volovsko Oko, Traminer Red and Zilavka. Heterozygous varieties are: Muscat Hamburg, Chasselas Buvie, Pearl of Csaba, Chasselas White, Italia, Italian Riesling, Merlo, Beli Medenac, Bagrina, Semillon, Pinot Noir, Prokupac, Å ljiva, Muscat Otonel.Varieties with functionally female flowers are probably homozygous, i. e.Ā Sf Sf. These are: Äaus and Crveni Drenak. In all combinations of crossings, seedlings having homogametic flower type were in deficit.Considering the improvement of grape varieties it is suggested to use hermaphrodite varieties of t he genetic constitutionĀ Sh Sh
Thermal effects in InGaAs/AlAsSb quantum-cascade lasers
A quantum-cascade laser (QCL) thermal model is presented. On the basis of a finite-difference approach, the model is used in conjunction with a self-consistent carrier transport model to calculate the temperature distribution in a near-infrared InGaAs/AlAsSb QCL. The presented model is used to investigate the effects of driving conditions and device geometries on the active-region temperature, which has a major influence on the device performance. A buried heterostructure combined with epilayer-down mounting is found to offer the best performance compared with alternative structures and has thermal time constants up to eight times smaller. The presented model provides a valuable tool for understanding the thermal dynamics inside a QCL and will help to improve operating temperatures
Evaluacija genotoksiÄnih efekata tiroksina primenom in vivo citogenetiÄkog testa na Swiss albino miÅ”evima
Thyroid hormones enhance aerobic metabolism favoring oxidative stress which may lead to covalent damage of various molecules including DNA. Previous investigations revealed that thyroid hormones induce DNA damage on human lymphocytes and sperm in the in vitro Comet assay. However, cytogenetic evaluation of genotoxic effects of thyroxine gave equivocal results: increase of sister chromatid exchanges, and no incerase of micronuclei in cultured human lymphocytes. Therefore, the aim of the present study was to further evaluate the possible genotoxic effects of thyroxine using in vivo cytogenetic test on Swiss albino mice. Three experimental concentrations of thyroxine were used (0.1 mg/kg, 0.5 mg/kg and 2.5 mg/kg). The mice were divided into several groups depending on the duration of the treatment with thyroxine. Thus, we treated mice for 1, 3, 7 and 10 days. Positive (Nmethyl- N'-nitro-N-nitrosoguanidine) and negative controls were also formed for the same time periods. Cytogenetic endpoinds (numerical and structural aberrations, chormosome gaps and breaks) were analysed in bone marrow cells from femures. The results obtained in this investigation showed that thyroxine has not induced chromosome damage or aberrations. This is in agreement with our previous analysis of micronuclei in human peripheral blood lymophocytes treated with thyroxine. On the other hand, we observed a decrease of mitotic index especially in animals treated for a longer period of time with the highest dose of thyroxine. Therefore, it can be concluded that thyroxine does not induce genotoxic effects which could be detected by cytogenetic analysis.Tireoidni hormoni podstiÄu aerobni metabolizam favorizujuÄi oksidativni stres koji može da dovede do kovalentnih oÅ”teÄenja razliÄitih molekula ukljuÄujuÄi i DNK. U prethodnim istraživanjima otkriveno je da tireoidni hormoni indukuju oÅ”teÄenja molekula DNK u humanim limfocitima i spermi u in vitro Komet testu. MeÄutim, citogenetiÄka evaluacija genotoksiÄnih efekata tiroksina dala je kontradiktorne rezultate: poveÄanje razmena sestrinskih hromatida bez porasta uÄesalosti mikronukleusa u kulturama humanih limfocita. Stoga je cilj istraživanja u ovom radu bio da dodatno ispitamo moguÄe genotoksiÄne efekte tiroksina koristeÄ i in vitro citogenetiÄki test na Swiss albino miÅ”evima. Upotrebljene su tri eksperimentalne koncentracije tiroksina (0,1 mg/kg, 0,5 mg/kg and 2.5 mg/kg). MiÅ”evi su podeljeni u nekoliko grupa zavisno od dužine tretmana tiroksinom: 1, 3, 7 i 10 dana. U istim vremenskim periodima miÅ”evi su tretirani pozitivnom (N-metil-N'-nitro-N-nitrozogvanidin) i negativnom kontrolom. Analizirani su citogenetiÄki parametri (numeriÄke i strukturne aberacije hromozoma, gapovi i prekidi na hromozomima) u Äelijama kostne srži izolovanim iz femura. Rezultati dobijeni u ovom istraživanju ukazuju da tiroksin ne indukuje hromozomske prekide i aberacije, Å”to je u saglasnosti sa naÅ”im prethodnim zapažanjima na humanim limfocitima u kulturi. Istovremeno, primetili smo smanjenje mitotskog indeksa, naroÄito kod životinja tretiranih u dužem vremenskom periodu sa visokim dozama tiroksina. Prema tome, može se zakljuÄiti da tiroksin ne indukuje genotoksiÄne efekte koji mogu da se detektuju citogenetiÄkim analizama
The Exchange of Tritiated Water Between Zn-A Zeolitevand the Surrounding Water
Zeolites are considered as adsorbents for tritiated waste water.
The sorption capacity of 4A zeolite is increased, and the speed
of tritium release, as THO, decreased if sodium ions in 4A zeolite
are replaced with small divalent cations. The exchange kinetics
THO/H20 between Zn-A zeolite containing tritiated water and the surrounding water was investigated at 30-60 De, using zinc-exchanged 4A zeolite beads of 0.8 and 1.6 mm radius. The kinetics was controlled by the diffusion of water in the solid particle and interpreted in terrns of the Boyd - Reichenberg diffusion model. Effective self-diffusion coefficients of water in the zeolite beads were obtained and the kinetic data are discussed from the point of view of using zeolites as sorbents and storage material for tritiated waste water
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