Memory Effects In Nonequilibrium Quantum Impurity Models

Memory effects play a key role in the dynamics of strongly correlated systems driven out of equilibrium. In the present study, we explore the nature of memory in the nonequilibrium Anderson impurity model. The Nakajima--Zwanzig--Mori formalism is used to derive an exact generalized quantum master equation for the reduced density matrix of the interacting quantum dot, which includes a non-Markovian memory kernel. A real-time path integral formulation is developed, in which all diagrams are stochastically sampled in order to numerically evaluate the memory kernel. We explore the effects of temperature down to the Kondo regime, as well as the role of source--drain bias voltage and band width on the memory. Typically, the memory decays on timescales significantly shorter than the dynamics of the reduced density matrix itself, yet under certain conditions it develops a smaller long tail. In addition we address the conditions required for the existence, uniqueness and stability of a steady-state.Comment: 4 pages, 3 figure

Pertumbuhan Dan Produksi Kacang Bogor (Vigna Subterranea (L.) Dengan Pemberian Pupuk P Dan Arang Sekam Padi

Pemberian pupuk anorganik dan organik dapat menyediakan unsur hara yang dibutuhkan oleh tanaman kacang bogor seperti unsur hara P. Sebagian fosfor di dalam tanah umumnya tidak tersedia untuk tanaman. Salah satu bahan organik yang mampu melepaskan unsur hara P adalah arang sekam padi. Penelitian ini bertujuan untuk mengetahui respons pertumbuhan dan produksi kacang bogor terhadap pemberian pupuk P dan arang sekam padi. Penelitian dilaksanakan di lahan Fakultas Pertanian Universitas Sumatera pada Juli – Oktober 2014. Penelitian ini menggunakan Rancangan Acak Kelompok (RAK) faktorial dengan 2 faktor dan 3 ulangan. Faktor pertama yaitu pemberian pupuk P dengan 4 taraf (0; 30; 60 dan 90 kg SP-36/ha) dan faktor kedua yaitu komposisi top soil dan arang sekam padi dengan 4 taraf (1:0; 1:1; 1:2 dan 2:1). Data yang diperoleh dianalisis dengan menggunakan sidik ragam dan dilanjutkan dengan uji jarak berganda Duncan. Peubah amatan yaitu jumlah cabang, umur berbunga, bobot polong, dan bobot biji. Hasil analisis data menunjukkan bahwa pemberian pupuk P berpengaruh dalam meningkatkan jumlah cabang, umur berbunga, bobot polong dan bobot biji. Pemberian arang sekam padi meningkatkan jumlah cabang Interaksi antara pemberian pupuk P dan arang sekam padi berpengaruh tidak nyata terhadap semua peubah amatan

A Fully Self-Consistent Treatment of Collective Fluctuations in Quantum Liquids

The problem of calculating collective density fluctuations in quantum liquids is revisited. A fully quantum mechanical self-consistent treatment based on a quantum mode-coupling theory [E. Rabani and D.R. Reichman, J. Chem. Phys.116, 6271 (2002)] is presented. The theory is compared with the maximum entropy analytic continuation approach and with available experimental results. The quantum mode-coupling theory provides semi-quantitative results for both short and long time dynamics. The proper description of long time phenomena is important in future study of problems related to the physics of glassy quantum systems, and to the study of collective fluctuations in Bose fluids.Comment: 9 pages, 4 figure

Spontaneous charge carrier localization in extended one-dimensional systems

Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally-tuned range-separated density functional theory and many-body perturbation calculations within the GW approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies and the optimally-tuned range parameter itself all become independent of polymer length as it exceeds the critical localization scale. Moreover, lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.Comment: 5 pages, 4 figure

Proportional Dynamics in Exchange Economies

We study the Proportional Response dynamic in exchange economies, where each player starts with some amount of money and a good. Every day, the players bring one unit of their good and submit bids on goods they like, each good gets allocated in proportion to the bid amounts, and each seller collects the bids received. Then every player updates the bids proportionally to the contribution of each good in their utility. This dynamic models a process of learning how to bid and has been studied in a series of papers on Fisher and production markets, but not in exchange economies. Our main results are as follows: - For linear utilities, the dynamic converges to market equilibrium utilities and allocations, while the bids and prices may cycle. We give a combinatorial characterization of limit cycles for prices and bids. - We introduce a lazy version of the dynamic, where players may save money for later, and show this converges in everything: utilities, allocations, and prices. - For CES utilities in the substitute range $[0,1)$, the dynamic converges for all parameters. This answers an open question about exchange economies with linear utilities, where tatonnement does not converge to market equilibria, and no natural process leading to equilibria was known. We also note that proportional response is a process where the players exchange goods throughout time (in out-of-equilibrium states), while tatonnement only explains how exchange happens in the limit.Comment: 25 pages, 6 figure