Reduced leakage current in Josephson tunnel junctions with codeposited barriers

Josephson junctions were fabricated using two different methods of barrier formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the first two layers were epitaxial. The oxide barrier was formed either by exposing the Al surface to O2 or by codepositing Al in an O2 background. The codeposition process yielded junctions that showed the theoretically predicted subgap current and no measurable shunt conductance. In contrast, devices with barriers formed by thermal oxidation showed a small shunt conductance in addition to the predicted subgap current.Comment: 3 pages, 4 figure

Зв’язок між виробничими функціями на підприємствах побутового обслуговування

В сучасних умовах актуальною науковою і практичною проблемою стає дослідження ролі і місце підприємств побутового обслуговування в процесах модернізації та інновації розвитку на регіональному рівні. Роль підприємств побутового обслуговування в економіці України і її регіонів, а також їх соціальне значення є досить вагомим. Ці підприємства надають можливість створювати нові робочі місця навіть під час економічної кризи, що знижує соціальну напругу і навантаження на ринок праці. Інтенсивному розвитку підприємств побутового обслуговування сприяє зростаючий споживацький попит на побутові послуги, що обумовлює необхідність ефективного управління підприємствами побутового обслуговування в стратегічному аспекті. Метою статті є дослідження зв’язку між виробничими функціями підприємств сфери обслуговування. Розглянуто функціонування малого підприємства, яке складається з двох ланок: хімчистка і пральня. В залежності від ефективності діяльності функціонування одного з двох підприємств аналітично побудовані виробничі функції. Використовуючи апарат економіко-математичного моделювання інвестиційної діяльності підприємства в роботі проаналізовані характеристики, які впливають на динаміку розвитку підприємства в цілому, на стратегію інвестування, яка відображає процеси самофінансування підприємства. Наведені рисунки показують різні моделі розвитку підприємств і дають можливість проаналізувати економічні показники функціонування підприємства що необхідно враховувати при побудові системи показників ефективності функціонування підприємств, які задіяні в побутовому секторі. Ця система повинна характеризувати ступінь результативності виробництва і здійснювати оцінку динаміки економічного ефекту при залученні додаткових ресурсів. Також необхідно забезпечити співвідношення економічних коефіцієнтів, які відповідають за інвестиції таким чином, щоб функціонування підприємства не зазнавало регресії чи стагнації, а працювало в оптимальному режимі в залежності від власних потужностей, соціальних потреб регіону тощо.Nowadays, the role and place of consumer services enterprises in the processes of modernization and development innovations at the regional level is becoming a topical scientific and practical problem. The role of household services in the economy of Ukraine and its regions, as well as their social significance, is quite important. These enterprises provide the opportunity to create new work places even during the economic crisis, which reduces social tension and the burden on the labour market. The intensive development of consumer services is supported by the growing consumer demand for domestic services, which necessitates the effective management of household services in the strategic aspect. The purpose of the article is to investigate the connection between the production functions of the service sector enterprises. We investigated the functioning of a small enterprise, which consists of two parts: dry cleaning and laundry. Depending on the functioning efficiency of one of the two companies, analytical production functions are built. Using the apparatus of economic-mathematical modelling of investment activity of the enterprise, were analysed the characteristics that affect the dynamics of the enterprise as a whole, on the investment strategy, which reflects the processes of self-financing of the enterprise. The given figures show different models of enterprise development and give an opportunity to analyse economic indicators of the functioning of an enterprise that need to be taken into account when constructing a system of indicators of the efficiency of functioning of enterprises that are involved in the domestic sector. This system should characterize the degree of performance of production and assess the dynamics of the economic effect of attracting additional resources. It is also necessary to ensure a ratio of economic coefficients that are responsible for the investment in such a way that the operation of the enterprise would not be subjected to regression or stagnation, but worked in the optimal mode depending on their own capacities, social needs of the region, etc

Point-contact study of the LuNi2B2C borocarbide superconducting film

We present point-contact (PC) Andreev-reflection measurements of a superconducting epitaxial c-axis oriented nickel borocarbide film LuNi2B2C (Tc=15.9 K). The averaged value of the superconducting gap is found to be 2.6 +/-0.2 meV in the one-gap approach, whereas the two-gap approach results in 2.14+/-0.36 meV and 3.0+/-0.27 meV. The better fit of the Andreev-reflection spectra for the LuNi2B2C - Cu PC obtained by the two-gap approach provides evidence for multiband superconductivity in LuNi2B2C. For the first time, PC electron-phonon interaction (EPI) spectra have been measured for this compound. They demonstrate pronounced phonon maximum at 8.5+/-0.4meV and a second shallow one at 15.8+/-0.6 meV. The electron-phonon coupling constant estimated from the PC EPI spectra turned out to be small (~ 0.1), like in other superconducting rare-earth nickel borocarbides. Possible reasons for this are discussed.Comment: 5 pages, 5 figures, V2: figs. 2 & 5 captions are corrected, and new Refs. 4, 6, 12, 13, 14 are adde

Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state

Point-contact (PC) spectroscopy measurements on antiferromagnetic (AF) (T_N=5.2K) HoNi2B2C single crystals in the normal and two different superconducting (SC) states (T_c=8.5K and $T_c^*=5.6K) are reported. The PC study of the electron-boson(phonon) interaction (EB(P)I) spectral function reveals pronounced phonon maxima at 16, 22 and 34meV. For the first time the high energy maxima at about 50meV and 100meV are resolved. Additionally, an admixture of a crystalline-electric-field (CEF) excitations with a maximum near 10meV and a `magnetic` peak near 3meV are observed. The contribution of the 10-meV peak in PC EPI constant \lambda_PC is evaluated as 20-30contribution of the high energy modes at 50 and 100meV amounts about 10each maxima, so the superconductivity might be affected by CEF excitations. The SC gap in HoNi2B2C exhibits a standard single-band BCS-like dependence, but vanishes at$T_c^*=5.6K<T_c, with 2\Delta/kT_c^*=3.9. The strong coupling Eliashberg analysis of the low-temperature SC phase with T_c^*=5.6K =T_N, coexisting with the commensurate AF structure, suggests a sizable value of the EPI constant \lambda_s=0.93. We also provide strong support for the recently proposed by us ''Fermi surface (FS) separation'' scenario for the coexistence of magnetism and superconductivity in magnetic borocarbides, namely, that the superconductivity in the commensurate AF phase survives at a special (nearly isotropic) FS sheet without an admixture of Ho 5d states. Above T_c^* the SC features in the PC characteristics are strongly suppressed pointing to a specific weakened SC state between T_c* and T_c.Comment: 11 pages, 8 figs, to be published in PRB, Vol.75, Iss.2

Short-term efficacy and usage recommendations for a large-scale implementation of the math-whizz tutor

This paper adds to the evidence of the efficacy of intelligent tutoring systems (ITS) in mathematics learning by evaluating a large-scale intervention at the state of Aguascalientes, Mexico. We report the results of a quasi-experimental study, addressing at the same a particular request of the decision-makers responsible for the rollout to provide, from early stages of the intervention, independent evidence of the efficacy of Math-Whizz Tutor beyond its internal metrics, and recommendations in terms of the expected weekly usage levels to guide the blended learning approach

Calculation of stress at bending of a beam of polymeric material

Розроблено математичну модель згину полімерної балки з нелінійним характером залежності між деформаціями та напруженнями.Разработана математическая модель изгиба полимерной балки с нелинейным характером зависимости между деформациями и напряжениями.The mathematical model of bend of polymer beams with non-linear relationship between the strain and the stress

Persistent currents in ballistic normal-metal rings

Recent experiments renewed interest in persistent currents in mesoscopic normal-metal rings. We show that in ballistic rings in high magnetic fields the Zeeman splitting leads to periodic current quenching with period much larger than the period of the persistent current. Simple arguments show that this effect might be relevant for diffusive rings as well. Another aim of this paper is to discuss fluctuations of the persistent current due to thermal excitation of high energy levels. Being observed such fluctuations would witness a coherent state of an electron system at high temperatures when the persistent current is exponentially suppressed.Comment: Submitted to Special Issue of the international journal Low Temperature Physics : "Quantum coherent effects in superconductors and normal metals" devoted to 75-years anniversary of Prof. Igor Kuli

Supercurrent noise in quantum point contacts

Spectral density of current fluctuations in a short ballistic superconducting quantum point contact is calculated for arbitrary bias voltages $V$. Contrary to a common opinion that the supercurrent flow in Josephson junctions is coherent process with no fluctuations, we find extremely large current noise that is {\em caused} by the supercurrent coherence. An unusual feature of the noise, besides its magnitude, is its voltage dependence: the noise decreases with increasing $V$, despite the fact that the dc current grows steadily with $V$. At finite voltages the noise can be qualitatively understood as the shot noise of the large charge quanta of magnitude $2\Delta /V$ equal to the charge transferred during one period of Josephson oscillations.Comment: 12 pages, revtex, 2 figures by fax/conventional mail upon reques

Probing Pseudogap by Josephson Tunneling

We propose here an experiment aimed to determine whether there are superconducting pairing fluctuations in the pseudogap regime of the high-$T_c$ materials. In the experimental setup, two samples above $T_c$ are brought into contact at a single point and the differential AC conductivity in the presence of a constant applied bias voltage between the samples, $V$, should be measured. We argue the the pairing fluctuations will produce randomly fluctuating Josephson current with zero mean, however the current-current correlator will have a characteristic frequency given by Josephson frequency $\omega_J = 2 e V /\hbar$. We predict that the differential AC conductivity should have a peak at the Josephson frequency with the width determined by the phase fluctuations time.Comment: 4 pages, 2 eps figure

Static Solitons of the Sine-Gordon Equation and Equilibrium Vortex Structure in Josephson Junctions

The problem of vortex structure in a single Josephson junction in an external magnetic field, in the absence of transport currents, is reconsidered from a new mathematical point of view. In particular, we derive a complete set of exact analytical solutions representing all the stationary points (minima and saddle-points) of the relevant Gibbs free-energy functional. The type of these solutions is determined by explicit evaluation of the second variation of the Gibbs free-energy functional. The stable (physical) solutions minimizing the Gibbs free-energy functional form an infinite set and are labelled by a topological number Nv=0,1,2,... Mathematically, they can be interpreted as nontrivial ''vacuum'' (Nv=0) and static topological solitons (Nv=1,2,...) of the sine-Gordon equation for the phase difference in a finite spatial interval: solutions of this kind were not considered in previous literature. Physically, they represent the Meissner state (Nv=0) and Josephson vortices (Nv=1,2,...). Major properties of the new physical solutions are thoroughly discussed. An exact, closed-form analytical expression for the Gibbs free energy is derived and analyzed numerically. Unstable (saddle-point) solutions are also classified and discussed.Comment: 17 pages, 4 Postscript figure