Electronic correlations in the Hubbard model on a bi-partite lattice

In this work we study the Hubbard model on a bi-partite lattice using the coupled-cluster method (CCM). We first investigate what, within this approach, allows us to reproduce the zero order parameter in the 1D model, as predicted by the exact solution. We show that we need a critical correlation in some of the coupled-cluster model coefficients to reproduce this result, as can be obtained by applying some very accurate results using the CCM for the Heisenberg model. Using the same approach we then tackle the 2D Hubbard model on a square and a honeycomb lattice, both of which can be thought to represent 2D materials. We also analyse the charge and spin excitations, with reasonable results.Comment: Major update to previous versio

Indoor Radio Propagation Measurements in Different Environments Using Two Types of Transmitting Antenna

The tremendous growth in Wireless Communications System has greatly increased the need to improve the accuracy of predicting signal propagation. It is important to have a tool that can be used to predict the signal coverage area, a method to determine the path loss in microcells, the attenuation due to different partitions and the effect of the environments. To understand radio propagation characteristics in buildings for Personal Communication Systems (PCSs), a comprehensive measurement was carried out in a shopping and business complex, The Mall, in Kuala Lumpur. Two types of Base Station (BS) antennas, Omni-directional and Panel antenna, were mounted on the ceiling and wall respectively. The Mobile Station (MS) uses an antenna with 3dB gain, height 0.5 m and 1.2 m respectively, at 935 MHz carrier frequency. Many test settings were chosen in the office, on the floor sharing with the atrium, lower ground floor and car park, with Line-of-Sight (LOS) and without LOS. The results show some variations of signal strengths with distance that have distinct near and far field regions. The buildings where the measurements were carried out typically have walls and columns constructed from concrete blocks. Within the building the time spread of arriving radio signals depends on reflections and scattering from the structure of the buildings. The results of these measurements are presented and discussed in order to investigate penetration losses in walls, soft boards and floors. The results showed that shadowing due to the objects has a greater influence on the signal strength than the distance between the transmitting and receiving antenna. The path loss within a building is linearly dependent on the logarithm of the distance, on the number of obstacles blocking the signal, on the number of walls between transmitter and receiver antenna, and on the number of floors vertically between the transmitter and receiver antennas. Another important factor is the type of the environment it is operating in, which is given as the factor n. Comparisons between predicted and measured results have shown that the model is capable of predicting the attenuation within the building for different environment

Intragastric balloons for obesity: critical review of device design, efficacy, tolerability, and unmet clinical needs

Introduction Sustaining a healthy weight is a challenge and obesity, with associated risk of co-morbidities, is a major public health concern. Bariatric surgery has shown a great promise for many where pharmacological and lifestyle interventions failed to work. However, challenges and limitations associated with bariatric surgery has pushed the demand for less invasive, reversible (anatomically) interventions, such as intragastric balloons (IGBs). Areas covered This review critically appraises IGBs used in the past, present, and those in clinical trials, discussing the device designs, limitations, placement and removal techniques, patient eligibility, efficacy, and safety issues. Expert opinion Several intragastric balloons were developed over the years that brought excitement to patients and healthcare professionals alike. Albeit good efficacy, there had been several safety issues reported with IGBs such as spontaneous deflation, intestinal occlusion, gut perforation, and mucosal ulcerations. This led to evolution of IGBs design; device material, filling mechanism, fluid type, inflation volume, and further innovations to ease ingestion and removal of device. There are some IGB devices under development aimed to swallow like a conventional pill and excrete naturally through defecation, however, how successful they will be in clinical practice in terms of their efficacy and tolerability remains to be seen in the future

On the value of counterfactual assessments in merger cases

The cost of erroneous decisions in merger cases could be huge. However, authorities cannot eradicate potential errors due to the ex-ante nature of merger control. Nevertheless, to minimiseerrors, stakeholders have formulated predictive techniques to aid assessments. One of the key means of engineering these techniques is through the use of counterfactuals. The problem, though, is that the status and value of such counterfactual assessments are far from clear. The lack of clarity has thus occasionally raised doubts about the nature, value, scope, and limitations of counterfactual assessments. The results may sound ‘scientific’, yet they are not. On the flip side, the process may appear overly elaborate, yet the result may be the best logical answer available. In light of the foregoing and in order to address all the different implications for mergers, this article explores the value of the counterfactual in providing relative accuracy. It gives a holistic account of the role of the counterfactual right from the point of market definition up until the stage of ex-post-evaluation. Specifically, it explains the role of the counterfactual in ascertaining the substitutability of products through the use of the hypothetical monopolist test. Further, it details the importance of the counterfactual in the assessment of market power. The article thereafter assesses the importance of ascertaining the right basis for the counterfactual. This is followed by the summary of the importance and consequence of the counterfactual assessment. The article also addresses the importance of the counterfactuals in efficiency analysis, failing firm defence and remedies

Experimentally validated quantum transport models for tunneling devices based on novel materials

The desire to reduce the power consumption of consumer electronics has driven the semiconductor industry to seek smaller transistors and to operate them at lower supply voltages. A reduction in the transistors dimensions by a certain fraction can reduce the power consumption by the same amount, for a specific operation speed. The semiconductor industry employs a 14nm feature size for its latest technology node and is pushing it down to 10nm. Moreover, reducing the supply voltage can also significantly lower the power consumption. However, the limit on the supply voltage is set by the threshold voltage, which is more than 0.6V given the fundamental limit of 60mV/dec for MOSFETs. Further reduction in supply voltage and consequently power consumption can be achieved with tunneling transistors that can overcome this limit. Tunneling transistors, however, face challenges with low ON current leading to slow performance. The ON current can be boosted by reducing the tunneling distance, either with a tight gate control in 2D materials or with internal piezo-polarization in nitrides. An accurate prediction of the performance of such nanoscale tunneling devices is obtained from experimentally validated quantum transport simulations. Two practical aspects have been added for a realistic prediction; incomplete ionization of doping and scattering effects on confined states in hetero-structures. Such additions have led to better agreements with relevant experimental measurements. The models have been employed to propose likely candidates towards future low power tunneling transistors based on novel materials and designs

An Ecological Survey of Benthic Invertebrates in Three Sites in Shatt-Al-Kufa at Al-Najaf Province, Iraq

      أجريت الدراسة الحالية من اجل التعرف على تركيب مجتمع اللافقريات القاعية فضلا عن دراسة بعض العوامل المرتبطة بنوعية المياه في شط الكوفة، تضمنت الدراسة اختيار ثلاثة مواقع في شط الكوفة، إذ جمعت عينات المياه ونماذج اللافقريات القاعية خلال الفترة من شهر شباط 2014 الى كانون الثاني 2015 .  شملت الدراسة اللااحيائية قياس كل من الكلوروفيل a والملوحة والمواد الصلبة الذائبة الكلية والمتطلب الكيموحيوي للأوكسجين والعسرة الكلية والنترات والكبريتات. أما الدراسة الإحيائية فتضمنت تحديد تركيب مجتمع اللافقريات القاعية من خلال دراسة كل من معدل الكثافة السكانية ومؤشر الوفرة النسبية لهذه الأحياء ودليل جاگارد للتشابه بين المواقع المدروسة. بلغ عدد اللافقريات القاعية التي جمعت في هذه الدراسة 28 وحدة تصنيفية توزعت على المجاميع الرئيسة الاربع الاتية (ثمان وحدات تصنيفية للديدان الحلقية وسبعة لمجموعة الحشرات وعشرة للنواعم وثلاث وحدات تصنيفية للديدان الخيطية)، وكانت اعلى نسبة للديدان الحلقية اذ بلغت 40.8% من مجموع اللافقريات القاعية تلتها الحشرات بنسبة 30.3 % ثم النواعم والديدان الخيطية بنسبة 28.4 %, 0.5% على التوالي. وقد اظهرت اللافقريات القاعية علاقات موجبة وسالبة مع العوامل الفيزيائية والكيميائية المدروسة.    The present study was conducted to determine the structure of benthic invertebrates community, as well as a study of some factors associated with water quality in Shatt Al-Kufa. The study was included a choice of three sites located along the Shatt Al-Kufa River, water samples and benthic invertebrates were collected during the period from February 2014 to January 2015.     The abiotic study included measurements of chlorophyll a, salinity, total dissolved solids, biochemical oxygen demand, total hardness, nitrate, and sulfate. The biotic study included the determination the composition of the benthic invertebrates community through the study of the mean population density, the relative abundance index of these organisms and the Jaccard Coefficient was calculated to identify the value of similarity between the studied sites. In the present study, 28 taxa of benthic invertebrates were recorded belong to 4 main groups which are: 8 taxa belonged to Annelida, 7 belonged to Insecta, 10 belonged to Mollusca, 3 belonged to Nematoda. Annelida recorded the highest percentage 40.8% of the total number of benthic invertebrates, Insecta with 30.3%, Mollusca and Nematoda with 28.4 %, 0.5% respectively. Benthic invertebrate has shown positive and negative relationships with the studied physical and chemical characteristics