Superfluid density of superconductor-ferromagnet bilayers

We report the first measurements of the effective superfluid density n_S(T) \propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where \lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers were sputtered in ultrahigh vacuum in quick succession onto oxidized Si substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni thickness long after T_C has stopped changing. We argue that this indicates a substantial superfluid density inside the ferromagnetic Ni films.Comment: 13 pages, 2 figures, MMM 2007 proceeding

Entropic Elasticity of Phantom Percolation Networks

A new method is used to measure the stress and elastic constants of purely entropic phantom networks, in which a fraction $p$ of neighbors are tethered by inextensible bonds. We find that close to the percolation threshold $p_c$ the shear modulus behaves as $(p-p_c)^f$, where the exponent $f\approx 1.35$ in two dimensions, and $f\approx 1.95$ in three dimensions, close to the corresponding values of the conductivity exponent in random resistor networks. The components of the stiffness tensor (elastic constants) of the spanning cluster follow a power law $\sim(p-p_c)^g$, with an exponent $g\approx 2.0$ and 2.6 in two and three dimensions, respectively.Comment: submitted to the Europhys. Lett., 7 pages, 5 figure

On the scaling approach to electron-electron interactions in a chaotic quantum dot

A scaling theory is used to study the low energy physics of electron-electron interactions in a double quantum dot. We show that the fact that electrons are delocalized over two quantum dots does not affect the instability criterion for the description of electron-electron interactions in terms of a ``universal interaction Hamiltonian''.Comment: 4 pages, 3 figure

Perbedaan Waktu Pengungkapan Status Diri ODHA Terhadap Pasangan Di Manado

Latar belakang : tahun 2015 kota Manado menempati urutan pertama di Propinsi Sulawesi Utara sebanyak 709 orang, yang teridentifikasi mengidap HIV sebanyak 223 orang, dan sisanya 486 orang mengidap AIDS Pada penderita HIV dan AIDS menurut kelompok umur terdapat peningkatan jumlah kasus di kelompok umur produktif yaitu dari usia remaja sampai dengan kelompok umur dewasa. Sedangkan pada kasus HIV AIDS menurut faktor resiko penularan, kelompok heteroseksual menempati posisi pertama. Tujuan : untuk menganalisis karakteristik ODHA terhadap pengungkapan status diri di Manado.Metode : jenis penelitian ini adalah penelitian kombinasi (mixed methods) yaitu pendekatan penelitian yang mengkombinasikan antara penelitian kuantitatif dan kualitatif. Dengan menggunakan teknik wawancara dan wawancara mendalam (Indepth Interview).Hasil : menunjukkan bahwa tidak ada perbedaan yang signifikan pengungkapan status diri ODHA berdasarkan karakteristik umur, jenis kelamin, pendidikan, status pasangan, penanggung biaya, dan keikutsertaan kelompok dukungan sebaya. Hal ini mengindikasikan bahwa pengungkapan status diri merupakan sebuah keputusan yang rumit karena menyangkut harga diri ODHA maupun keluarganya, mengingat label Stigma dan diskriminasi yang terus mengancam integritas jati diri ODHA dan keluarga.Kesimpulan : penelitian ini merekomendasikan kepada Dinas Kesehatan Provinsi Sulawesi Utara sebagai bahan masukan dalam membuat kebijakan dan pengembangan layanan program kesehatan reproduksi khususnya dalam pencegahan dan penanggulangan penyakit HIV dan AIDS

Comparison of the full-potential and frozen-core approximation approaches to density-functional calculations of surfaces

We scrutinize the accuracy of the pseudopotential approximation in density-functional theory (DFT) calculations of surfaces by systematically comparing to results obtained within a full-potential setup. As model system we choose the CO oxidation at a RuO2(110) surface and focus in particular on the adsorbate binding energies and reaction barriers as target quantities for the comparison. Rather surprisingly, the major reason for discrepancy does not result from the neglected semi-core state relaxation in the frozen-core approximation, but from an inadequate description of the local part of the Ru pseudopotential, responsible for the scattering of f like waves. Tiny, seemingly irrelevant, imprecisions appearing in these properties can have a noticeable influence on the surface energetics. At least for the present example, we obtain excellent agreement between both approaches, if the pseudopotential describes these scattering properties accurately.Comment: 8 pages including 3 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Hydrodynamical Models of Outflow Collimation in YSOs

We explore the physics of time-dependent hydrodynamic collimation of jets from Young Stellar Objects (YSOs). Using parameters appropriate to YSOs we have carried out high resolution hydrodynamic simulations modeling the interaction of a central wind with an environment characterized by a moderate opening angle toroidal density distribution. The results show that the the wind/environment interaction produces strongly collimated supersonic jets. The jet is composed of shocked wind gas. Using analytical models of wind blown bubble evolution we show that the scenario studied here should be applicable to YSOs and can, in principle, initiate collimation on the correct scales (R ~ 100 AU). The simulations reveal a number of time-dependent non-linear features not anticipated in previous analytical studies including: a prolate wind shock; a chimney of cold swept-up ambient material dragged into the bubble cavity; a plug of dense material between the jet and bow shocks. We find that the collimation of the jet occurs through both de Laval nozzles and focusing of the wind via the prolate wind shock. Using an analytical model for shock focusing we demonstrate that a prolate wind shock can, by itself, produce highly collimated supersonic jets.Comment: Accepted by ApJ, 31 pages with 12 figures (3 JPEG's) now included, using aasms.sty, Also available in postscript via a gzipped tar file at ftp://s1.msi.umn.edu/pub/afrank/SFIC1/SFIC.tar.g

Orbital Ferromagnetism and Quantum Collapse in Stellar Plasmas

The possibility of quantum collapse and characteristics of nonlinear localized excitations is examined in dense stars with Landau orbital ferromagnetism in the framework of conventional quantum magnetohydrodynamics (QMHD) model including Bohm force and spin-orbit polarization effects. Employing the concepts of effective potential and Sagdeev pseudopotential, it is confirmed that the quantum collapse and Landau orbital ferromagnetism concepts are consistent with the magnetic field and mass-density range present in some white dwarf stars. Furthermore, the value of ferromagnetic-field found in this work is about the same order of magnitude as the values calculated earlier. It is revealed that the magnetosonic nonlinear propagations can behave much differently in the two distinct non-relativistic and relativistic degeneracy regimes in a ferromagnetic dense astrophysical object. Current findings should help to understand the origin of the most important mechanisms such as gravitational collapse and the high magnetic field present in many compact stars.Comment: To appear in journal Physics of Plasma

Qubit-induced phonon blockade as a signature of quantum behavior in nanomechanical resonators

The observation of quantized nanomechanical oscillations by detecting femtometer-scale displacements is a significant challenge for experimentalists. We propose that phonon blockade can serve as a signature of quantum behavior in nanomechanical resonators. In analogy to photon blockade and Coulomb blockade for electrons, the main idea for phonon blockade is that the second phonon cannot be excited when there is one phonon in the nonlinear oscillator. To realize phonon blockade, a superconducting quantum two-level system is coupled to the nanomechanical resonator and is used to induce the phonon self-interaction. Using Monte Carlo simulations, the dynamics of the induced nonlinear oscillator is studied via the Cahill-Glauber $s$-parametrized quasiprobability distributions. We show how the oscillation of the resonator can occur in the quantum regime and demonstrate how the phonon blockade can be observed with currently accessible experimental parameters

Quasiprobabilistic Interpretation of Weak measurements in Mesoscopic Junctions

The impossibility of measuring noncommuting quantum mechanical observables is one of the most fascinating consequences of the quantum mechanical postulates. Hence, to date the investigation of quantum measurement and projection is a fundamentally interesting topic. We propose to test the concept of weak measurement of noncommuting observables in mesoscopic transport experiments, using a quasiprobablistic description. We derive an inequality for current correlators, which is satisfied by every classical probability but violated by high-frequency fourth-order cumulants in the quantum regime for experimentally feasible parameters.Comment: 4 pages, published versio