Variational Quantum Monte Carlo Method with a Neural-Network Ansatz for Open Quantum Systems

The possibility to simulate the properties of many-body open quantum systems with a large number of degrees of freedom is the premise to the solution of several outstanding problems in quantum science and quantum information. The challenge posed by this task lies in the complexity of the density matrix increasing exponentially with the system size. Here, we develop a variational method to efficiently simulate the non-equilibrium steady state of Markovian open quantum systems based on variational Monte Carlo and on a neural network representation of the density matrix. Thanks to the stochastic reconfiguration scheme, the application of the variational principle is translated into the actual integration of the quantum master equation. We test the effectiveness of the method by modeling the two-dimensional dissipative XYZ spin model on a lattice

Decentralized Dynamic Hop Selection and Power Control in Cognitive Multi-hop Relay Systems

In this paper, we consider a cognitive multi-hop relay secondary user (SU) system sharing the spectrum with some primary users (PU). The transmit power as well as the hop selection of the cognitive relays can be dynamically adapted according to the local (and causal) knowledge of the instantaneous channel state information (CSI) in the multi-hop SU system. We shall determine a low complexity, decentralized algorithm to maximize the average end-to-end throughput of the SU system with dynamic spatial reuse. The problem is challenging due to the decentralized requirement as well as the causality constraint on the knowledge of CSI. Furthermore, the problem belongs to the class of stochastic Network Utility Maximization (NUM) problems which is quite challenging. We exploit the time-scale difference between the PU activity and the CSI fluctuations and decompose the problem into a master problem and subproblems. We derive an asymptotically optimal low complexity solution using divide-and-conquer and illustrate that significant performance gain can be obtained through dynamic hop selection and power control. The worst case complexity and memory requirement of the proposed algorithm is O(M^2) and O(M^3) respectively, where $M$ is the number of SUs

The Art of Insight in Science and Engineering

Tools to make hard problems easier to solve.In this book, Sanjoy Mahajan shows us that the way to master complexity is through insight rather than precision. Precision can overwhelm us with information, whereas insight connects seemingly disparate pieces of information into a simple picture. Unlike computers, humans depend on insight. Based on the author's fifteen years of teaching at MIT, Cambridge University, and Olin College, The Art of Insight in Science and Engineering shows us how to build insight and find understanding, giving readers tools to help them solve any problem in science and engineering.To master complexity, we can organize it or discard it. The Art of Insight in Science and Engineering first teaches the tools for organizing complexity, then distinguishes the two paths for discarding complexity: with and without loss of information. Questions and problems throughout the text help readers master and apply these groups of tools. Armed with this three-part toolchest, and without complicated mathematics, readers can estimate the flight range of birds and planes and the strength of chemical bonds, understand the physics of pianos and xylophones, and explain why skies are blue and sunsets are red.The Art of Insight in Science and Engineering will appear in print and online under a Creative Commons Noncommercial Share Alike license

Recognizing when a preference system is close to admitting a master list

A preference system $\mathcal{I}$ is an undirected graph where vertices have preferences over their neighbors, and $\mathcal{I}$ admits a master list if all preferences can be derived from a single ordering over all vertices. We study the problem of deciding whether a given preference system $\mathcal{I}$ is close to admitting a master list based on three different distance measures. We determine the computational complexity of the following questions: can $\mathcal{I}$ be modified by (i) $k$ swaps in the preferences, (ii) $k$ edge deletions, or (iii) $k$ vertex deletions so that the resulting instance admits a master list? We investigate these problems in detail from the viewpoint of parameterized complexity and of approximation. We also present two applications related to stable and popular matchings.Comment: 30 pages, 1 figure. Reason for update: additional discussion on the Kemeny Score problem, and correction of some typo

Indonesia dalam Liberalisasi Perdagangan (Perspektif Politik dan Budaya Hukum)

In this discussion, the author tries to illustrate the complexity of the problems or weakrtesses Indonesian involvement in trade liberalization, both in terms of aspects of political, legal and cultural aspects related to the position of Indonesia as a developing country. Based on all the above explanation, then that should be a basic question in this paper, namely: What factors the complexity of the weakrtess of Indonesia in trade liberalization. There are some problems or weakrtesses is the basis why it failed to achieve the interests and economic benefits expected Indonesian government, namely (1) The weakrtess of economic diplomacy. Negotiators consisting of diplomats and officials of the technical departments have weaknesses. Diplomats may dominate in terms of language but not in terms of substance, while officials from the technical department to master the substance but did not master the language. This weakness is compounded because of the very few institutions both have members who master the skills to design a legal sentence. (2) Lack of awareness and attitude of the national industry to utilize the legal instruments of trade remedies. (3) The weakness of the latter which will be discussed in this paper is related to the bargaining position of developing countries when dealing with the industrialized countries

Nested Weighted Limit-Average Automata of Bounded Width

While weighted automata provide a natural framework to express quantitative properties, many basic properties like average response time cannot be expressed with weighted automata. Nested weighted automata extend weighted automata and consist of a master automaton and a set of slave automata that are invoked by the master automaton. Nested weighted automata are strictly more expressive than weighted automata (e.g., average response time can be expressed with nested weighted automata), but the basic decision questions have higher complexity (e.g., for deterministic automata, the emptiness question for nested weighted automata is PSPACE-hard, whereas the corresponding complexity for weighted automata is PTIME). We consider a natural subclass of nested weighted automata where at any point at most a bounded number k of slave automata can be active. We focus on automata whose master value function is the limit average. We show that these nested weighted automata with bounded width are strictly more expressive than weighted automata (e.g., average response time with no overlapping requests can be expressed with bound k=1, but not with non-nested weighted automata). We show that the complexity of the basic decision problems (i.e., emptiness and universality) for the subclass with k constant matches the complexity for weighted automata. Moreover, when k is part of the input given in unary we establish PSPACE-completeness

Efficient Stochastic Simulations of Complex Reaction Networks on Surfaces

Surfaces serve as highly efficient catalysts for a vast variety of chemical reactions. Typically, such surface reactions involve billions of molecules which diffuse and react over macroscopic areas. Therefore, stochastic fluctuations are negligible and the reaction rates can be evaluated using rate equations, which are based on the mean-field approximation. However, in case that the surface is partitioned into a large number of disconnected microscopic domains, the number of reactants in each domain becomes small and it strongly fluctuates. This is, in fact, the situation in the interstellar medium, where some crucial reactions take place on the surfaces of microscopic dust grains. In this case rate equations fail and the simulation of surface reactions requires stochastic methods such as the master equation. However, in the case of complex reaction networks, the master equation becomes infeasible because the number of equations proliferates exponentially. To solve this problem, we introduce a stochastic method based on moment equations. In this method the number of equations is dramatically reduced to just one equation for each reactive species and one equation for each reaction. Moreover, the equations can be easily constructed using a diagrammatic approach. We demonstrate the method for a set of astrophysically relevant networks of increasing complexity. It is expected to be applicable in many other contexts in which problems that exhibit analogous structure appear, such as surface catalysis in nanoscale systems, aerosol chemistry in stratospheric clouds and genetic networks in cells

Enhancing students’ confidence, competence and knowledge with Integrated Skills Challenge

Introduction/background: In today's complex healthcare environment, new nursing graduates are expected to master nursing skills in a timely manner and become critical thinkers with the capacity of solving complex healthcare problems efficiently. The increased complexity of the clinical setting requires competence-building begin in introductory courses, establishing foundational skills for critical thinking and prioritisation. In the healthcare professions, teaching and learning methods are focused on integration of clinical knowledge and skills. However, traditional teaching and learning methodologies do not always facilitate the development of a requisite level of these clinical skills. For the Master of Nursing Studies (MNSt) students whose program is shortened this means the acquisition of these skills must be achieved more rapidly. Aim/objectives: The purpose of this study is to investigate the feasibility of developing simulation scenarios (Integrated Skill Challenge [ISC]) as a supplemental teaching-learning strategy to enhance the transfer of student self-confidence and competence to the clinical nursing environment. Methods To examine potential effects of ISC on the MNSt students, a pilot study was conducted including 52 participants. Data were collected weekly over 11 week period by using pre and post-test design. Results: Analysis showed a significant increase in the confidence, competence and knowledge. Confidence, competence and knowledge scores increased when students were pre-loaded with knowledge prior to performing in the ISC. Results generally indicated that the ISC had the anticipated effects. Conclusions: This study reveals a high feasibility of developing simulation scenarios as an active learning methodology and that it should be developed further and piloted on a larger sample

TECHNIQUES IN MAKING MASTER MODEL FOR SPIN CASTING TECHNOLOGY

A master model is required before a product is actually processed in a machine. One technique to produce this master model is using Roland MDX 40 machine which is already used in ADTC. However, duplicating master model by using this machine is not recommended because : (1) Producing a master model using a Roland MDX 40 machine consumes a long time (depend on product complexity) due to metal material used for producing the master model is a heat resistant material, hence requires more time to shape; (2) Roland MDX 40 machine are high costly to use. The time consumption in the process of making the master model would burden the cost of electricity and replacing the cutter all the time when it is not sharp anymore; (3) A Roland MDX 40 machine also requires a machine operator to always stand by to frequently giving the machine and cutter oil lubricant during the process. This research use PDPC (Process Decision Program Chart) to depict all of the techniques that did in ordering to obtain the best technique in making master model. Fishbone diagram used to analyze the problems that occur on every technique. Arrow diagram used to detect the sequence of production process and obtain production time. By the end of the research, A prototype machine was built to produce a master model of UAJY keychain. This machine operates at 1400 rpm, with power of 187,5 watt, price of IDR 4.500.000,00 and machine cost per hour is IDR 1.650,00