Field emission testing of carbon nanotubes for THz frequency vacuum microtube sources

A carbon nanotube-based high current density electron field emission source is under development at Jet Propulsion Laboratory (JPL) for submillimeter-wave power generation (300 GHz to 3 THz). This source is the basis for a novel vacuum microtube component: the nanoklystron. The nanoklystron is a monolithically fabricated reflex klystron with dimensions in the micrometer range. The goal is to operate this device at much lower voltages than would be required with hot-electron sources and at much higher frequencies than have ever been demonstrated. Both single-walled (SWNTs) as well as multi-walled nanotubes (MWNTs) are being tested as potential field-emission sources. This paper presents initial results and observations of these field emission tests. SWNTs and MWNTs were fabricated using standard CVD techniques. The tube density was higher in the case of MWNT samples. As previously reported, high-density samples suffered from enhanced screening effect thus decreasing their total electron emission. The highest emission currents were measured from disordered, less dense MWNTs and were found to be ~0.63 mA @ 3.6 V/μm (sample 1) and ~3.55 mA @ 6.25 V/μm (sample 2). The high density vertically aligned MWNTs showed low field emission as predicted: 0.31 mA @ 4.7 V/μm

Organizational Culture Factors Affect Employees’ Organizational Commitment: A Research in Ho Chi Minh City Logistics Enterprises, Vietnam

Research aims: The research aims to evaluate several factors of organizational culture affecting the organizational commitment of employees in logistics enterprises in Ho Chi Minh City (Vietnam).Design/Methodology/Approach: The data were collected based on a survey of respondents who were employees working at logistics enterprises in Ho Chi Minh City. The collected data, consisting of 227 survey questionnaires, were described through statistical analysis, checking Cronbach’s Alpha reliability assessment, employing Exploratory Factor Analysis (EFA), and testing the fit of the research model. Research findings: The results showcased that five components had a statistically significant impact on an employee’s organizational commitment, including (from high to low impact in order) consistency in governance policy, communication within the organization, training and development, rewards and recognition, and teamwork.Theoretical contribution/Originality: The study contributes to and supplements the array of organizational culture topics related to the commitment of employees at companies.Practitioner/Policy implication: The research contributes to the logistics companies' understanding of how to improve the organizational culture to maintain the loyalty of employees in the organization.Research limitation/Implication: The research limitation is that only Ho Chi Minh City logistics enterprises were chosen for the survey. However, there are many cities in Vietnam where logistics companies are located. Thus, the other research can be implemented in other regions in Vietnam and other countries for future studies

Taxonomic notes on the genus Euaspis Gerstäcker (Hymenoptera: Apoidea: Megachilidae) from Vietnam

Taxonomic notes on species of the genus Euaspis Gerstäcker, 1858 (Hymenoptera: Megachilidae) from Vietnam are presented. Three species of the genus are reported: E. aequicarinata Pasteels is recorded in the central highlands Vietnam (Kon Tum Province) beside the previous record of this species in the northwest (Hoa Binh Province); E. polynesia Vachal is widely recorded throughout Vietnam; the taxonomy of Vietnamese Euaspis basalis (Ritsema, 1874) is a misidentification, and it is indeed Euaspis diversicarinata Pasteels, 1980 and is a new record from Vietnam. A key to the females of Vietnamese species of Euaspis Gerstäcker and a redescription of the female of E. diversicarinata are given with illustrations

Laguerre polynomials and the inverse Laplace transform using discrete data

We consider the problem of finding a function defined on $(0,\infty)$ from a countable set of values of its Laplace transform. The problem is severely ill-posed. We shall use the expansion of the function in a series of Laguerre polynomials to convert the problem in an analytic interpolation problem. Then, using the coefficients of Lagrange polynomials we shall construct a stable approximation solution.Comment: 14 page

Perforator Mapping of the Superficial and Deep Inferior Epigastric Artery in the Abdominal Region of the Vietnamese

BACKGROUND: Previous studies worldwide have investigated the anatomy of the perforators of the deep inferior epigastric arteries to figure out the navigation patterns of the perforators on the abdominal wall. This has been inconsistent amongst the researchers about how to select the perforator to increase the blood supply area for the flap. AIM: To explore the blood supply area of the perforators of the superficial and deep inferior epigastric artery in the abdominal region of the Vietnamese by dissection and 64-slice multislice computed tomography (64-slice MSCT). METHODS: A descriptive cross-sectional study Center from September 2014 to September 2016 on two groups including 30 cadavers fixed by formalin 10% in Anatomy Department of UPNT, and 37 patients getting the 64-slice MSCT abdominal arteries angiogram. RESULTS: The superficial epigastric arteries at the level of the inguinal ligament were located in the middle region, with 96% (right) and 88.5% (left). The anterior superior iliac spine level was in the middle, and lateral regions of 68% and 32% respectively. The level of the umbilical cord was in the lateral region with 66.7% and 85.7%, respectively. There were about 6 perforators of the deep inferior epigastric arteries located in the navel area. These perforators were 70% in the medial region and 30% in the middle region. CONCLUSION: Mapping the blood supply based on the fourth space in the abdominal region in which the superfical inferior epigastric arteries supplied the lateral area. The middle and the internal ones were the perforators of the deep inferior epigastric arteries

Analyze the Determinants of Capital Structure for Vietnamese Real Estate Listed Companies

This study adopts a two - step system general method of moments (GMM) approach towards investigating the determinants of capital structure for the listed real estate firms on Ho Chi Minh stock exchange (HSX) in Viet Nam from 2010 to 2015. The determinants of capital structure are mixed and different for short-term and long-term indicators. The real estate firms tend to use more debts to finance their investment. Vietnamese real estate firms should focus on balance structure debt due to complicated impacts of the determinants to their capital structure. There are some implications for the real estate companies and policy of the Government that are based on the empirical results. Keywords: determinants of capital structure, real estate company, general method of moments. JEL Classifications: G32, R

SECURITY CAPABILITY ANALYSIS OF COGNITIVE RADIO NETWORK WITH SECONDARY USER CAPABLE OF JAMMING AND SELF-POWERING

This paper investigates a cognitive radio network where a secondary sender assists a primarytransmitter in relaying primary information to a primary receiver and also transmits its own information toa secondary recipient. This sender is capable of jamming to protect secondary and/or primary informationagainst an eavesdropper and self-powering by harvesting radio frequency energy of primary signals.Security capability of both secondary and primary networks are analyzed in terms of secrecy outageprobability. Numerous results corroborate the proposed analysis which serves as a design guidelineto quickly assess and optimize security performance. More importantly, security capability trade-offbetween secondary and primary networks can be totally controlled with appropriate selection of systemparameters

Field emission testing of carbon nanotubes for THz frequency vacuum microtube sources

A carbon nanotube-based high current density electron field emission source is under development at Jet Propulsion Laboratory (JPL) for submillimeter-wave power generation (300 GHz to 3 THz). This source is the basis for a novel vacuum microtube component: the nanoklystron. The nanoklystron is a monolithically fabricated reflex klystron with dimensions in the micrometer range. The goal is to operate this device at much lower voltages than would be required with hot-electron sources and at much higher frequencies than have ever been demonstrated. Both single-walled (SWNTs) as well as multi-walled nanotubes (MWNTs) are being tested as potential field-emission sources. This paper presents initial results and observations of these field emission tests. SWNTs and MWNTs were fabricated using standard CVD techniques. The tube density was higher in the case of MWNT samples. As previously reported, high-density samples suffered from enhanced screening effect thus decreasing their total electron emission. The highest emission currents were measured from disordered, less dense MWNTs and were found to be ~0.63 mA @ 3.6 V/μm (sample 1) and ~3.55 mA @ 6.25 V/μm (sample 2). The high density vertically aligned MWNTs showed low field emission as predicted: 0.31 mA @ 4.7 V/μm