51 research outputs found
Non-linear effects in hopping conduction of single-crystal La_{2}CuO_{4 + \delta}
The unusual non-linear effects in hopping conduction of single-crystal
La_{2}CuO_{4 + \delta} with excess oxygen has been observed. The resistance is
measured as a function of applied voltage U (10^{-3} V - 25 V) in the
temperature range 5 K 0.1 V) the
conduction of sample investigated corresponds well to Mott's variable-range
hopping (VRH). An unusual conduction behavior is found, however, in low voltage
range (approximately below 0.1 V), where the influence of electric field and
(or) electron heating effect on VRH ought to be neglected. Here we have
observed strong increase in resistance at increasing U at T < 20 K, whereas at
T > 20 K the resistance decreases with increasing U. The magnetoresistance of
the sample below 20 K has been positive at low voltage and negative at high
voltage. The observed non-Ohmic behavior is attributable to inhomogeneity of
the sample, and namely, to the enrichment of sample surface with oxygen during
the course of the heat treatment of the sample in helium and air atmosphere
before measurements. At low enough temperature (below 20 K) the surface layer
with increased oxygen concentration is presumed to consist of disconnected
superconducting regions (with T_{c} about 20 K) in poor-conducting matrix. The
results obtained demonstrate that transport properties of cuprate oxides may be
determined in essential degree by structural or stoichimetric inhomogeneities.
This should be taken into account at evaluation of "quality" of
high-temperature superconductors on the basis of transport properties
measurements.Comment: 12 pages, REVTex, 11 Postscript figures, To be published in Fizika
Nizkikh Temperatur (published by AIP as Low Temperature Physics
Magnetoresistive study of antiferromagnetic--weak ferromagnetic transition in single-crystal LaCuO
The resistive measurements were made to study the magnetic field-induced
antiferromagnetic (AF) - weak ferromagnetic (WF) transition in LaCuO
single-crystal. The magnetic field (DC or pulsed) was applied normally to the
CuO layers. The transition manifested itself in a drastic decrease of the
resistance in critical fields of ~5-7 T. The study is the first to display the
effect of the AF -WF transition on the conductivity of the LaCuO
single-crystal in the parallel - to - CuO layers direction. The results
provide support for the 3-dimensional nature of the hopping conduction of this
layered oxide.Comment: 8 pages, 7 figures, RevTe
Transport, thermal and magnetic properties of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_2O_{10-\delta}, a magnetic superconductor
Resistivity, thermoelectric power, heat capacity and magnetization for
samples of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_{2}O_{10-\delta} were investigated in the
temperature range 1.8-300 K with a magnetic field up to 8 T. The resistive
transitions to the superconducting state are found to be determined by the
inhomogeneous (granular) structure, characterized by the intragranular, T_{c0},
and intergranular, T_{cg}, transition temperatures. Heat capacity, C(T), shows
a jump at the superconducting transition temperature T_{c0}\approx 37.5 K. A
Schottky-like anomaly is found in C(T) below 20 K. This low temperature anomaly
can be attributed to splitting of the ground term of paramagnetic
Gd^{3+} ions by internal and external magnetic fields.Comment: 3 pages (4 figs. incl.), reported at 50th Magnetism and Magnetic
Materials Conference, San Jose, CA, USA, 200
Resistive and magnetoresistive properties of CrO2 pressed powders with different types of inter-granular dielectric layers
Resistive, magnetoresistive and magnetic properties of four kinds of pressed
CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been
investigated. The particles in powders constituted of rounded particles
(diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm
and average length of 302 nm. All of the particles had a surface dielectric
shell of varying thickness and different types (such as oxyhydroxide -CrOOH or
chromium oxide Cr2O3). For all the samples at low temperatures we found
non-metallic temperature dependence of resistivity and giant negative
magnetoresistance (MR). The maximum value of MR at low temperatures (T \approx
5 K) is \approx 37% in relatively small fields (0.5 T). At higher temperatures
there was a rapid decrease of MR (up to \approx 1% / T at T \approx 200 K). The
main objective of this work was studying the influence of properties and
thickness of the intergranular dielectric layers, as well as CrO2 particle
shape, on the magnitude of the tunneling resistance and MR of the pressed
powder. The new results obtained in this study include: (1) detection at low
temperatures in powders with needle-like particles a new type of MR hysteresis,
and nonmonotonic MR behaviour with increasing magnetic field (absolute value of
the MR at first grows rather rapidly with the field, and then begins
diminishing markedly, forming a maximum), and (2) detection of non-monotonic
temperature dependence, where - a field in which the resistance in a magnetic
field has a maximum, as well as finding discrepancies in values of and
coercivity fields, (3) detection of the anisotropy of MR, depending on the
relative orientation of the transport current and the magnetic field, (4) a new
method of synthesis, to regulate the thickness of dielectric coating.Comment: 19 pages, 8 figure
Characteristic crossing point ( K) in specific-heat curves of samples RuSrGdCeCuO taken for different values of magnetic field
Magnetic properties of polycrystalline samples of
RuSr(GdCe)CuO, as-prepared (by
solid-state reaction) and annealed (12 hours at 845C) in pure oxygen
at different pressure (30, 62 and 78 atm) are presented. Specific heat and
magnetization were investigated in the temperature range 1.8--300 K with a
magnetic field up to 8 T. Specific heat, , shows a jump at the
superconducting transition (with onset at K). Below 20 K, a
Schottky-type anomaly becomes apparent in . This low-temperature anomaly
can be attributed to splitting of the ground term of paramagnetic
Gd ions by internal and external magnetic fields. It is found that
curves taken for different values of magnetic field have the same
crossing point (at K) for all samples studied. At the
same time, curves taken for different temperatures have a crossing point
at a characteristic field T. These effects can be
considered as manifestation of the crossing-point phenomenon which is supposed
to be inherent for strongly correlated electron systems.Comment: 10 pages, 7 figures, submitted to J. Phys.: Condens. Matte
Critical properties of two-dimensional Josephson junction arrays with zero-point quantum fluctuations
We present results from an extensive analytic and numerical study of a
two-dimensional model of a square array of ultrasmall Josephson junctions. We
include the ultrasmall self and mutual capacitances of the junctions, for the
same parameter ranges as those produced in the experiments. The model
Hamiltonian studied includes the Josephson, , as well as the charging,
, energies between superconducting islands. The corresponding quantum
partition function is expressed in different calculationally convenient ways
within its path-integral representation. The phase diagram is analytically
studied using a WKB renormalization group (WKB-RG) plus a self-consistent
harmonic approximation (SCHA) analysis, together with non-perturbative quantum
Monte Carlo simulations. Most of the results presented here pertain to the
superconductor to normal (S-N) region, although some results for the insulating
to normal (I-N) region are also included. We find very good agreement between
the WKB-RG and QMC results when compared to the experimental data. To fit the
data, we only used the experimentally determined capacitances as fitting
parameters. The WKB-RG analysis in the S-N region predicts a low temperature
instability i.e. a Quantum Induced Transition (QUIT). We carefully simulations
and carry out a finite size analysis of as a function of the
magnitude of imaginary time axis . We find that for some relatively
large values of (, the
limit does appear to give a {\it non-zero} , while
for , . We use the SCHA to analytically understand
the dependence of the QMC results with good agreement between them.
Finally, we also carried out a WKB-RG analysis in the I-N region and found no
evidence of a low temperature QUIT, up to lowest order in Comment: 39 pages, 18 postscript figures, to appear in Phys. Rev.
Percolation model for the superconductor-insulator transition in granular films
We study the temperature dependence of the superconductor-insulator
transition in granular superconductors. Empirically, these systems are
characterized by very broad resistance tails, which depend exponentially on the
temperature, and the normal state resistance. We model these systems by a
two-dimensional random resistor percolation networks in which the resistance
between two grains is governed either by Josephson junction coupling or by
quasi particle tunneling. Our numerical simulations as well as an effective
medium evaluation explain the experimental results over a wide range of
temperatures and resistances. Using effective medium approximation we find an
analytical expression for the effective resistance of the system and the value
of the critical resistance separating conducting from insulating branches.Comment: 4 pages, 2 figure
Популяционная перестройка Т-лимфоцитов, содержащих хемокиновые рецепторы, у пациентов с хронической обструктивной болезнью легких
Summary. Chronic obstructive pulmonary disease (COPD) is a difficult-to-treat progressive disease. About 14.7–68.6 % of COPD cases are not related to smoking. We examined 21 nonsmokers with COPD, 20 smokers with COPD, 20 healthy nonsmokers and 21 healthy smokers. Relative number of peripheral blood T-lymphocytes containing CCR5 and CXCR3 chemokine receptors was determined by flow cytometry. CXCR3+ and CCR5+ T-cell per cent number was increased in non-smokers with COPD compared with healthy non-smokers. A higher proportion of T-cells containing CCR5 and CXCR3 receptors on the cell surface was also observed in blood of smokers with COPD compared both to healthy smokers and nonsmokers. Our findings suggest similar mechanism of T-cells migration from blood into the airways both in non-smoking and smoking patients.Резюме. Хроническая обструктивная болезнь легких (ХОБЛ) – прогрессирующее заболевание, которое плохо поддается лечению. От 14,7 до 68,6 % случаев ХОБЛ не связаны с курением. Методом проточной цитометрии определено относительное количество Т-лимфоцитов крови, содержащих хемокиновые рецепторы CXCR3 и CCR5. Были обследованы 21 некурящий пациент с ХОБЛ, 20 курящих больных ХОБЛ, 20 здоровых некурящих людей и 21 здоровый курильщик. У некурящих пациентов с ХОБЛ наблюдалось увеличение процента CXCR3+ и CCR5+ Т-лимфоцитов по сравнению со здоровыми некурящими людьми. Установлено также повышение доли Т-клеток, содержащих на своей поверхности рецепторы ССR5 и CXCR3, в общей популяции лимфоцитов крови у курящих пациентов с ХОБЛ по сравнению со здоровыми курящими и некурящими людьми. Результаты исследования свидетельствуют о схожем механизме миграции Т-клеток из кровотока в дыхательные пути у некурящих и курящих пациентов
Geographical Distribution, Incidence, Malignancies, and Outcome of 136 Eastern Slavic Patients With Nijmegen Breakage Syndrome and NBN Founder Variant c.657_661del5
Nijmegen breakage syndrome (NBS) is a DNA repair disorder characterized by combined immunodeficiency and a high predisposition to lymphoid malignancies. The majority of NBS patients are identified with a homozygous five base pair deletion in the Nibrin (NBN) gene (c.657_661del5, p.K219fsX19) with a founder effect observed in Caucasian European populations, especially of Slavic origin. We present here an analysis of a cohort of 136 NBS patients of Eastern Slav origin across Belarus, Ukraine, Russia, and Latvia with a focus on understanding the geographic distribution, incidence of malignancy, and treatment outcomes of this cohort. Our analysis shows that Belarus had the highest prevalence of NBS (2.3 per 1,000,000), followed by Ukraine (1.3 per 1,000,000), and Russia (0.7 per 1,000,000). Of note, the highest concentration of NBS cases was observed in the western regions of Belarus and Ukraine, where NBS prevalence exceeds 20 cases per 1,000,000 people, suggesting the presence of an “Eastern Slavic NBS hot spot.” The median age at diagnosis of this cohort ranged from 4 to 5 years, and delay in diagnosis was more pervasive in smaller cities and rural regions. A total of 62 (45%) patients developed malignancies, more commonly in males than females (55.2 vs. 34.2%; p=0.017). In 27 patients, NBS was diagnosed following the onset of malignancies (mean age: 8 years). Malignancies were mostly of lymphoid origin and predominantly non-Hodgkin lymphoma (NHL) (n=42, 68%); 38% of patients had diffuse large B-cell lymphoma. The 20-year overall survival rate of patients with malignancy was 24%. However, females with cancer experienced poorer event-free survival rates than males (16.6% vs. 46.8%, p=0.036). Of 136 NBS patients, 13 underwent hematopoietic stem cell transplantation (HSCT) with an overall survival of 3.5 years following treatment (range: 1 to 14 years). Indications for HSCT included malignancy (n=7) and immunodeficiency (n=6). Overall, 9% of patients in this cohort reached adulthood. Adult survivors reported diminished quality of life with significant physical and cognitive impairments. Our study highlights the need to improve timely diagnosis and clinical management of NBS among Eastern Slavs. Genetic counseling and screening should be offered to individuals with a family history of NBS, especially in hot spot regions. © Copyright © 2021 Sharapova, Pashchenko, Bondarenko, Vakhlyarskaya, Prokofjeva, Fedorova, Savchak, Mareika, Valiev, Popa, Tuzankina, Vlasova, Sakovich, Polyakova, Rumiantseva, Naumchik, Kulyova, Aleshkevich, Golovataya, Minakovskaya, Belevtsev, Latysheva, Latysheva, Beznoshchenko, Akopyan, Makukh, Kozlova, Varabyou, Ballow, Ong, Walter, Kondratenko, Kostyuchenko and Aleinikova.We thank all doctors for clinical help for patients. We also appreciate the support of patient and their parents for agreeing to take part in this study. TP thanks Sergey?Nikulshin, Marika Grutupa, and Zanna Kovalova. We thank Joseph Dasso for editing this manuscript, primarily for proper English
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