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Broadband electroluminescence from reverse breakdown in individual suspended carbon nanotube pn-junctions

Nano Research 2020年第10期13卷 2857-2861页

作者： Bo Wang Sisi Yang Yu Wang Younghee Kim ragib ahsan Rehan K.apadia Stephen KDoorn Han Htoon Stephen B.Cronin Department of Physics and Astronormy University of Southern CalforniaLos AngelesCA 90089USA Ming Hsieh Department of Electrical Engineering University of Southern CaliforniaLos AngelesCA 90089USA Mork Farmily Department of Chemical Engineering and Materials Science University of Southern CaliforniaLos AngelesCA 90089USA Center for Integrated Nanotechnologies Materials Physics and Applications DivisionLos Alamos National LaboratoryLos AlamosNM 87545USA

There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral emission characteristics that provide important information regarding the underlying physical processes that lead to photon emission. Here, we report spectra obtained from individual suspended CNT dual-gate field effect transistor (FET) devices under different gate and bias conditions. By applying opposite voltages to the gate electrodes (i.e., Vg1 = –Vg2), we are able to create a pn-junction within the suspended region of the CNT. Under forward bias conditions, the spectra exhibit a peak corresponding to E11 exciton emission via thermal (i.e., blackbody) emission occurring at electrical powers around 8 μW, which corresponds to a power density of approximately 0.5 MW/cm2. On the other hand, the spectra observed under reverse bias correspond to impact ionization and avalanche emission, which occurs at electrical powers of ~ 10 nW and exhibits a featureless flat spectrum extending from 1,600 nm to shorter wavelengths up to 600 nm. Here, the hot electrons generated by the high electric fields (~ 0.5 MV/cm) are able to produce high energy photons far above the E11 (ground state) energy. It is somewhat surprising that these devices do not exhibit light emission by the annihilation of electrons and holes under forward bias, as in a light emitting diode (LED). Possible reasons for this are discussed, including Auger recombination.

关键词： ballistic avalanche high-field band-to-band photoemission

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Analysis of Rate One Quasi-Orthogonal Space-Time Block Coding over Rayleigh Fading Channel

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International Journal of Communications, Network and System Sciences 2014年第6期7卷 196-202页

作者： Md. Abdullah Al Amin Ranju ragib Shakil Rafi Electronics & Communication Engineering Khulna University Khulna Bangladesh

Full-rate is very important in any data transmission coding. For transmitting data at low bit rate than full-rate code, higher modulation scheme is required. But it is impossible to design full rate orthogonal designs with complex constellation for more than two transmit antennas. Only Alamouti code provides full-rate for two transmit antennas. In this paper, Bit Error Rate (BER) is calculated for Quasi-Orthogonal Space-time Block Coding (QOSTBC). Here we work with Rayleigh fading channel. We consider the codes which decodes pairs of symbols instead of simple separate decoding like Orthogonal Space-Time Block Coding. In Quasi-Orthogonal Space-time Block Code full-rate is achieved but full-diversity is sacrificed. Diversity is the most important techniques for providing reliable communication over fading channels. One of the diversity techniques that uses multiple transmit and/or receive antennas is space diversity. Multiple antenna technique provides a space diversity to struggle with the fading without necessarily sacrificing bandwidth resources, so the excellent solutions of removing the fading of the channel for broadband wireless communications is using space diversity. Then, with the constellation rotation of the symbol, rotated version of Quasi-Orthogonal Space-Time Block Code is generated. It provides full diversity. We simulate BER for QOSTBC, rotated QOSTBC, orthogonal STBC and for uncoded system. The simulation result shows that QOSTBC and rotated QOSTBC perform better than other systems. It shows that QOSTBC provides a full transmission rate but that rotated QOSTBC provides the full rate with the full diversity.

关键词： Orthogonal Space-Time Block Coding Quasi-Orthogonal Space-Time Block Coding Rayleigh Fading Rotated Quasi-Orthogonal Space-Time Block Coding

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Analysis of the Effect of Air Hole Diameter and Lattice Pitch in Optical Properties for Hexagonal Photonic Crystal Fiber

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Optics and Photonics Journal 2015年第7期5卷 227-233页

作者： Sagor Biswas ragib Shakil Rafi Md. Abdullah Al-Amin Sabbir Alam Electronics and Communication Engineering (ECE) Discipline Khulna University Khulna Bangladesh

We have investigated the different optical properties such as confinement loss, waveguide dispersion of a five rings hexagonal photonic crystal fiber under varied air hole diameter (d), lattice pitch (Λ), and air hole diameter to lattice pitch ratio for three different materials fused quartz glass, borosilicate glass and sapphire glass. We observed low confinement loss and high negative dispersion at higher d/Λ. Achieving high d/Λ can be done in two ways: increasing the air hole diameter or decreasing the lattice pitch. It has been observed, increasing the air hole diameter has significant effect over reducing lattice pitch in achieving low confinement loss. On the other hand, decreasing the lattice pitch over increasing the air hole diameter has significant effect in achieving high negative dispersion. It has also been found that, effective refractive index (neff) decreases significantly when lattice pitch decreases.

关键词： Photonic Crystal Fiber Dispersion Air Hole Diameter Lattice Pitch Effective Refractive Index

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Clinical Characteristics of COVID-19 Patients with Digestive Symptoms in a Tertiary Level Hospital

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Open Journal of Gastroenterology 2022年第9期12卷 232-248页

作者： Dilip Kumar Ghosh Akhlak Ahmed Hafez Mohammad Nazmul ahsan Parash Ullah Mukta Nath Syed Alamgir Safwath Department of Gastroenterology Shaheed Suhrawardy Medical College Hospital Sher-e-Bangla Nagar Dhaka Bangladesh Department of Medicine Shaheed Suhrawardy Medical College Hospital Sher-e-Bangla Nagar Dhaka Bangladesh Sir Salimullah Medical College Dhaka Bangladesh Department of Gastroenterology Jalalabad Ragib-Rabeya Medical College Sylhet Bangladesh

Background: The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has greatly challenged public health worldwide. A growing number of studies have reported gastrointestinal (GI) symptoms. The study aimed to estimate the various digestive symptoms frequently reported in Covid-19 patients among the adult population of Bangladesh. Methods: In this descriptive, cross-sectional study, we enrolled confirmed patients with COVID-19 who were admitted to the COVID unit of Shaheed Suhrawardy Medical college hospital, Dhaka from July 2020 to December 2020. All patients were COVID confirmed by real-time polymerase chain reaction (RT-PCR) and were analyzed for clinical characteristics, laboratory findings and imaging study. Results: The study population consisted of 121 COVID-19-positive patients, among them, 57.85% were male and 42.15% female. The majority (43%) of the study population were in the age group of 31 - 40 years. The male to female ratio was 1.4:1. Nearly 94.2% of the sample population were married, among them 92.9% were male and 96.1% were female. Out of 121 Covid-19 patients, 30.65% had a contact history, 17.4% had a history of traveling or residing in an area reporting COVID-19 and 11.6% of family members were affected by Covid-19. Most of the patients had a fever (95%), cough (88.4%) and dyspnoea (43.8%), pneumonia (37.4%) and severe pneumonia (36.4%). In this study, 40% patients reported a digestive symptom including diarrhea 47.9%, vomiting 55.5%, loss of appetite 16.5%, abdominal pain 29.8%, abdominal bloating 24.8%, reflux 0%, jaundice 3.3%. Regarding co-morbidities, the majority had bronchial asthma (50%) followed by hypertension 46%, diabetes 38%, obesity 23%, and CKD 14% and heart disease 3%. Among 121 COVID-19 patients, 98% had recovered from the disease and 2% of patients expired. Conclusion: Gastrointestinal symptoms are common among patients with COVID-19 and this group of patients had a long time of hospital sta

关键词： COVID-19 Gastrointestinal Symptoms Diarrhoea Prognosis Fecal-Oral-Transmission

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