On sign-changeable interaction in FLRW cosmology

We investigate an interacting two-fluid model in a spatially flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) Universe, when the energy transfer between these two dark components is produced by a factorisable nonlinear sign-changeable interaction depending linearly on the energy density and quadratically on the deceleration parameter. We solve the source equation and obtain the effective energy densities of the dark sector and their components. We show that the effective equation of state of the dark sector includes some of the several kind of Chaplygin gas equations of state as well as a generalization of the polytropic equation of state. We use bayesian statistics methods to constrain free parameters in the models during its most recent evolution considering supernovae type Ia and measurements of the Hubble expansion rate. The resulting constraints provide new information on sign-changeable interactions, its equivalences and compatibility with previous models and novel late time universe dynamics.Comment: 8 figure

Peningkatan hasil belajar Matematika melalui Modil pembelajaran Kooperatif tipe Think Pairs Share(TPS) bagi siswa Kelas IV Sekolah Dasar Negeri 3 Kalongan Kecamatan Purwodadi Kabupaten Grobogan Tahun Pelajaran 2011/2012

Penelitian ini bertujuan untuk meningkatkan hasil belajar siswa dalam pembelajaran matematika melalui model pembelajaran kooperatif tipe think pairs share (TPS). Dalam penelitian ini merupakan penelitian tindakan kelas (PTK) terdiri dari dua siklus, tiap siklus terdiri dari lima tahapan yaitu perencanaan, pelaksanaan, observasi, refleksi dan evaluasi. Lokasi penelitian ini di SD Negeri 3 Kalongan Kecamatan Purwodadi Kabupaten Grobogan. Sebagai subjek penerima tindakan adalah siswa kelas IV yang berjumlah 13 siswa, terdiri dari 9 siswa lakilaki dan 4 siswa perempuan, dan subjek pelaksanaan tindakan adalah peneliti dan guru matematika kelas IV. Metode pengumpulan data yang digunakan dalam penelitian ini adalah wawancara, observasi, tes, dan dokumentasi. Untuk menjamin validitas data digunakan teknik triangulasi sumber dan trianggulasi tehnik. Trianggulasi sumber yaitu mencocokkan data hasil belajar siswa dengan hasil pengamatan langsung terhadap aktivitas belajar siswa. Trianggulasi tehnik yaitu metode pengumpulan data yang berasal dari hasil observasi, wawancara, dan tes. Tehnik analisis data yang digunakan adalah analisis interaktif yang terdiri dari reduksi data, penyajian data dan penarikan kesimpulan. Hasil penelitian ini adalah adanya peningkatan hasil belajar siswa melalui model pembelajaran kooperatif tipe Think Pairs Share (TPS). Hal ini dapat dilihat pada pra siklus rata-rata kelas 59,23, siswa yang mencapai KKM 4 (30,76%); pada siklus I meningkat nilai rata-rata kelas menjadi 61,35 siswa yang mencapai KKM 5 (38,46%); pada siklus II meningkat nilai rata-rata kelas menjadi 67,69, siswa yang mencapai KKM 10 (76,92%). Kesimpulan penelitian ini adalah dengan menerapakan model pembelajaran kooperatif tipe Think Pairs Share (TPS) dapat meningkatkan hasil belajar siswa kelas IV SD Negeri 3 Kalongan kecamatan Purwodadi Kabupaten Grobogan Tahun Ajaran 2011/2012

Improved diffusion Monte Carlo for bosonic systems using time-step extrapolation "on the fly"

A diffusion Monte Carlo algorithm employing "on the fly" extrapolation with respect to the time step is implemented and demonstrated simulating realistic systems. Significant advantages are obtained when using on the fly extrapolation, leading to reduced systematic and statistical errors. The sound theoretical basis of extrapolation on the fly is discussed and compared to justifications for the a posteriori extrapolation

Decomposition of homogeneous polynomials with low rank

Let $F$ be a homogeneous polynomial of degree $d$ in $m+1$ variables defined over an algebraically closed field of characteristic zero and suppose that $F$ belongs to the $s$-th secant varieties of the standard Veronese variety $X_{m,d}\subset \mathbb{P}^{{m+d\choose d}-1}$ but that its minimal decomposition as a sum of $d$-th powers of linear forms $M_1, ..., M_r$ is $F=M_1^d+... + M_r^d$ with $r>s$. We show that if $s+r\leq 2d+1$ then such a decomposition of $F$ can be split in two parts: one of them is made by linear forms that can be written using only two variables, the other part is uniquely determined once one has fixed the first part. We also obtain a uniqueness theorem for the minimal decomposition of $F$ if the rank is at most $d$ and a mild condition is satisfied.Comment: final version. Math. Z. (to appear

Structure and energetics of ammonia clusters (NH3)n (n=3-20) investigated using a rigid-polarizable model derived from ab initio calculations

An analytical model has been developed to describe the interaction between rigid ammonia molecules including the explicit description of induction. The parameters of the model potential were chosen by fitting high quality ab initio data obtained using second-order Moller-Plesset (MP2) perturbation theory and extended basis sets. The description of polarization effects is introduced by using a noniterative form of the "charge on spring model", the latter accounting for more than 95% of the dipole induction energy and of the increased molecular dipole. Putative global minima for (NH3)(n) (n = 3-20) have been optimized using this new model, the structure and energetics of the clusters with n = 3-5 being found in good agreement with previous ab initio results including electronic correlation. Results for larger species have been compared with previous structural studies where only nonpolarizable models were employed. Our model predicts larger binding energies for any cluster size than previous analytical surfaces, the results often suggesting a reorganization of the relative energy ranking and a different structure for the global minimum

Reorganization Law and Dilution Threats in Different Financial Systems

In a market-based financial system, credit is held by dispersed creditors, and out-of-court renegotiation of debt is more likely to fail because of hold-out problems; in a bank-based system, out-of-court renegotiation stands good chances to succeed. Since out-of-court renegotiation is a substitute for court-supervised reorganization, the design of a reorganization law cannot abstract from the financial system. Chapter 11-style renegotiation is shown to benefit public debt firms and to be harmful for private debt firms; the overall effect depends on the financial system, but is likely to be positive only in a market-based system. The case for a reorganization law is weakened if dilution threats like exit consents are taken into account: such a law is then in most cases undesirable. Legislation, however, which jointly introduces a reorganization law while facilitating the use of dilution threats will improve welfare in a market-based system, but reduce welfare in a bank-based system. Thus, the paper indentifies a new determinant in the debate over optimal bankruptcy codes, which is how easily dilution threats can be deployed.Workouts;reorganization law;Chapter 11;financial systems;dilution threats;exit consents;hold-in effect

Thermodynamic properties of ammonia clusters (NH(3))(n) n=2-11: Comparing classical and quantum simulation results for hydrogen bonded species

Classical and quantum simulations of ammonia clusters in the dimer through the hendecamer range are performed using the stereographic projection path integral. Employing the most recent polarizable potential to describe intermolecular interactions, energetic and structural data obtained with our simulations provide support for a more fluxional or flexible nature at low temperature of the ammonia dimer, pentamer, and hexamer than in the other investigated species. The octamer and the hendecamer display a relatively strong melting peak in the classical heat capacity and a less intense but significant melting peak in the quantum heat capacity. The latter are shifted to lower temperature (roughly 15 and 40 K lower, respectively) by the quantum effects. The features present in both classical and quantum constant volume heat capacity are interpreted as an indication of melting even in the octamer case, where a large energy gap is present between its global minimum and second most stable species. We develop a first order finite difference algorithm to integrate the geodesic equations in the inertia ellipsoid generated by n rigid nonlinear bodies mapped with stereographic projections. We use the technique to optimize configurations and to explore the potential surface of the hendecamer

Collateral, Renegotiation and the Value of Diffusely Held Debt

Debt with many creditors is analyzed in a continuous-time pricing model of the levered firm. We specifically allow for debtor opportunism vis-a-vis a non-coordinated group of creditors, in form of repeated strategic renegotiation offers and default threats. We show that the creditors' initial entitlement to non-collateralized assets will be expropriated through exchange offers. Exchange offers successively increase the level of collateral until all assets are fully collateralized. The ex ante optimal debt contract is neither fully collateralized nor without any collateral. Diffusely held debt allows for a larger debt capacity and bears lower credit risk premia than privately held debt. We derive simple closed-form solutions for the value of equity and defaultable bonds. Numerical estimates show that the bond valuation is very sensitive to the correct specification of the debt renegotiation model.Debt reorganization;multiple creditors

Improved diffusion Monte Carlo propagators for bosonic systems using Ito calculus

The construction of importance sampled diffusion Monte Carlo (DMC) schemes accurate to second order in the time step is discussed. A central aspect in obtaining efficient second order schemes is the numerical solution of the stochastic differential equation (SDE) associated with the Fokker-Plank equation responsible for the importance sampling procedure. In this work, stochastic predictor-corrector schemes solving the SDE and consistent with It\uf4 calculus are used in DMC simulations of helium clusters. These schemes are numerically compared with alternative algorithms obtained by splitting the Fokker-Plank operator, an approach that we analyze using the analytical tools provided by It\uf4 calculus. The numerical results show that predictor-corrector methods are indeed accurate to second order in the time step and that they present a smaller time step bias and a better efficiency than second order split-operator derived schemes when computing ensemble averages for bosonic systems. The possible extension of the predictor-corrector methods to higher orders is also discussed