NUMERICAL STUDIES ON VERTICAL TUBULAR GENERATOR IN VAPOR ABSORPTION REFRIGERATION SYSTEM

PASUPATHY BALAMURUGAN,ANNAMALAI MANI 대한설비공학회 2011 International Journal Of Air-Conditioning and Refr Vol.19 No.2

A model has been developed based on Colburn–Drew type formulation to analyze a vertical tube in tube stainless steel generator with forced convective boiling. Desorption of refrigerant vapor from refrigerant–absorbent solution takes place in the inner tube of the generator, when hot water through the annulus is used as heating medium. Simultaneous heat and mass transfer phenomena of desorption are described mathematically using the mass and energy balances, considering the heat and mass transfer resistances in liquid as well as vapor phases. Model equations are solved simultaneously by means of initial value problem solvers using explicit Runge–Kutta method with 4th order accuracy. A computer code has been developed in MATLAB to obtain the results. A parametric analysis has also been performed to study the effect of various parameters on the performance of the generator.

A Tutorial: Applications of Clinical Self-Efficacy Principles to Mentoring of SLP Assistants

Rubini Pasupathy,Renee Bogschutz,Rajinder Koul 한국언어재활사협회 2017 Clinical Archives of Communication Disorders Vol.2 No.1

There are an increasing number of speech-language pathology assistants (SLP-As) in the public school settings under the supervision of speech-language pathologists (SLPs) in the United States. One of the functions of SLPs is to mentor and facilitate the development of SLP-As. The primary aim of this tutorial is to use the social cognitive model of self-efficacy to enhance the knowledge and skills of SLP-As. Literature in social cognitive theory indicates that self-efficacy is a predictor of performance, particularly in education and health domains. Effectively incorporating the self-efficacy framework in the mentoring of SLP-As will improve clinical performance and outcomes, as well as increase job satisfaction and retention of SLP-As in the school setting.

Rehabilitation Sciences Doctoral Education: A Study of Audiology, Speech-Language Therapy, and Physical Therapy Students’ Research Self-Efficacy Beliefs

Rubini Pasupathy 한국언어재활사협회 2018 Clinical Archives of Communication Disorders Vol.3 No.1

Purpose: The primary purpose of this study is to add to the existing knowledge base on the research self-efficacy beliefs and research productivity of doctoral students in Rehabilitation Sciences, and its influence on research productivity. Identifying and understanding the research beliefs of Rehabilitation Sciences doctoral students will provide a better understanding of the factors that facilitate research consumption and productivity with implications for improving and enhancing Rehabilitation Sciences doctoral education. Methods: This study employed a convenience sample of doctoral students at a public research institution of higher education enrolled in Rehabilitation Sciences programs that include; Doctor of Audiology, Communication Sciences and Disorders PhD, Physical Therapy Doctor of Science-Research Track, Physical Therapy Doctor of Science-Educational Track, and PhD in Rehabilitation Sciences. The Research Self-efficacy Inventory was utilized to measure the research self-efficacy of doctoral students in Rehabilitation Sciences programs. Results: Research track doctoral students compared to clinical doctoral students reported higher research self-efficacy and research productivity. Conclusions: Mastery and vicarious experiences may have contributed to increasing the research self-efficacy beliefs of research track doctoral students.

One year changes in QCT and DXA bone densities following bariatric surgery in a multiethnic Asian cohort

Hong Chang Tan,Matthew Zhen-Wei Tan,Kwang Wei Tham,Shanker Pasupathy,Alvin Kim Hock Eng,Sonali Ganguly,Oi Fah Lai,Alvin Choong Meng Ng 대한골다공증학회 2015 Osteoporosis and Sarcopenia Vol.1 No.2

Objectives: Bone loss after bariatric surgery is well recognized but the best method for quantifying bone mineral density (BMD) remains controversial. BMD measured with dual energy X-ray absorptiometry (DXA) is prone to measurement errors in this population while quantitative computed tomography (QCT) is less affected. We report the skeletal changes after bariatric surgery at 1-year in a multi-ethnic Asian cohort using both central DXA and QCT. Methods: Areal BMD (aBMD) and volumetric BMD (vBMD) of twenty-two participants (mean age 40.6; female 59%) undergoing sleeve gastrectomy (n ¼ 12) or gastric bypass (n ¼ 10) were measured with central DXA and QCT respectively before and 12-months after surgery. Results: Weight and BMI decreased significantly but discordant QCT and DXA results were noted. aBMD was significantly reduced at the total hip (TH) and femoral neck (FN) by 6.9 and 8.5% respectively but was not significantly different at the lumbar spine (LS). By contrast, there were no significant changes in vBMD at TH and FN. Instead, a significant 11.2% decrease in vBMD was noted at the LS. These findings were largely similar between the two surgical subgroups. Interestingly, cortical vBMD increased at both TH and FN while trabecular vBMD decreased at the TH. These changes were observed despite no significant post-operative changes in serum calcium, iPTH or 25-OH vitamin D levels. Conclusion: Technical or physiological factors may be involved in the discordance between QCT and DXA results during short-term follow-up and the most suitable method of bone density measurement for post-bariatric surgery patients remains uncertain. © 2015 The Korean Society of Osteoporosis. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Klein tunnelling and electron trapping in nanometre-scale graphene quantum dots

Gutié,rrez, Christopher,Brown, Lola,Kim, Cheol-Joo,Park, Jiwoong,Pasupathy, Abhay N. Nature Publishing Group 2016 NATURE PHYSICS Vol.12 No.11

Relativistic fermions that are incident on a high potential barrier can pass through unimpeded, a striking phenomenon termed the ‘Klein paradox’ in quantum electrodynamics. Electrostatic potential barriers in graphene provide a solid-state analogue to realize this phenomenon. Here, we use scanning tunnelling microscopy to directly probe the transmission of electrons through sharp circular potential wells in graphene created by substrate engineering. We find that electrons in this geometry display quasi-bound states where the electron is trapped for a finite time before escaping via Klein tunnelling. We show that the continuum Dirac equation can be successfully used to model the energies and wavefunctions of these quasi-bound states down to atomic dimensions. We demonstrate that by tuning the geometry of the barrier it is possible to trap particular energies and angular momentum states with increased efficiency, showing that atomic-scale electrostatic potentials can be used to engineer quantum transport through graphene.

Atomistic Interrogation of B–N Co-dopant Structures and Their Electronic Effects in Graphene

Schiros, Theanne,Nordlund, Dennis,Palova, Lucia,Zhao, Liuyan,Levendorf, Mark,Jaye, Cherno,Reichman, David,Park, Jiwoong,Hybertsen, Mark,Pasupathy, Abhay American Chemical Society 2016 ACS NANO Vol.10 No.7

<P>Chemical doping has been demonstrated to be an effective method for producing high-quality, large-area graphene with controlled carrier concentrations and an atomically tailored work function. The emergent optoelectronic properties and surface reactivity of carbon nanostructures are dictated by the microstructure of atomic dopants. Co-doping of graphene with boron and nitrogen offers the possibility to further tune the electronic properties of graphene at the atomic level, potentially creating p- and n-type domains in a single carbon sheet, opening a gap between valence and conduction bands in the 2-D semimetal. Using a suite of high-resolution synchrotron-based X-ray techniques, scanning tunneling microscopy, and density functional theory based computation we visualize and characterize B–N dopant bond structures and their electronic effects at the atomic level in single-layer graphene grown on a copper substrate. We find there is a thermodynamic driving force for B and N atoms to cluster into BNC structures in graphene, rather than randomly distribute into isolated B and N graphitic dopants, although under the present growth conditions, kinetics limit segregation of large B–N domains. We observe that the doping effect of these BNC structures, which open a small band gap in graphene, follows the B:N ratio (B > N, p-type; B < N, n-type; BN, neutral). We attribute this to the comparable electron-withdrawing and -donating effects, respectively, of individual graphitic B and N dopants, although local electrostatics also play a role in the work function change.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2016/ancac3.2016.10.issue-7/acsnano.6b01318/production/images/medium/nn-2016-01318z_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn6b01318'>ACS Electronic Supporting Info</A></P>

Atomic-Scale Spectroscopy of Gated Monolayer MoS₂

Zhou, Xiaodong,Kang, Kibum,Xie, Saien,Dadgar, Ali,Monahan, Nicholas R.,Zhu, X.-Y.,Park, Jiwoong,Pasupathy, Abhay N. American Chemical Society 2016 NANO LETTERS Vol.16 No.5

<P>The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS<SUB>2</SUB> by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal–organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS<SUB>2</SUB>. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS<SUB>2</SUB> film at a density of 1.3 × 10<SUP>12</SUP> eV<SUP>–1</SUP> cm<SUP>–2</SUP>. By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2016/nalefd.2016.16.issue-5/acs.nanolett.6b00473/production/images/medium/nl-2016-004733_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl6b00473'>ACS Electronic Supporting Info</A></P>

Large Physisorption Strain in Chemical Vapor Deposition of Graphene on Copper Substrates

He, Rui,Zhao, Liuyan,Petrone, Nicholas,Kim, Keun Soo,Roth, Michael,Hone, James,Kim, Philip,Pasupathy, Abhay,Pinczuk, Aron American Chemical Society 2012 Nano letters Vol.12 No.5

<P>Graphene single layers grown by chemical vapor deposition on single crystal Cu substrates are subject to nonuniform physisorption strains that depend on the orientation of the Cu surface. The strains are revealed in Raman spectra and quantitatively interpreted by molecular dynamics (MD) simulations. An average compressive strain on the order of 0.5% is determined in graphene on Cu(111). In graphene on Cu (100), MD simulations interpret the observed highly nonuniform strains.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-5/nl300397v/production/images/medium/nl-2012-00397v_0001.gif'></P>

Dopant Segregation in Polycrystalline Monolayer Graphene

Zhao, Liuyan,He, Rui,Zabet-Khosousi, Amir,Kim, Keun Soo,Schiros, Theanne,Roth, Michael,Kim, Philip,Flynn, George W.,Pinczuk, Aron,Pasupathy, Abhay N. American Chemical Society 2015 Nano letters Vol.15 No.2

<P>Heterogeneity in dopant concentration has long been important to the electronic properties in chemically doped materials. In this work, we experimentally demonstrate that during the chemical vapor deposition process, in contrast to three-dimensional polycrystals, the substitutional nitrogen atoms avoid crystal grain boundaries and edges over micron length scales while distributing uniformly in the interior of each grain. This phenomenon is universally observed independent of the details of the growth procedure such as temperature, pressure, substrate, and growth precursor.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-2/nl504875x/production/images/medium/nl-2014-04875x_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl504875x'>ACS Electronic Supporting Info</A></P>

Via Method for Lithography Free Contact and Preservation of 2D Materials

Telford, Evan J.,Benyamini, Avishai,Rhodes, Daniel,Wang, Da,Jung, Younghun,Zangiabadi, Amirali,Watanabe, Kenji,Taniguchi, Takashi,Jia, Shuang,Barmak, Katayun,Pasupathy, Abhay N.,Dean, Cory R.,Hone, Ja American Chemical Society 2018 NANO LETTERS Vol.18 No.2

<P>Atomically thin 2D materials span the common components of electronic circuits as metals, semiconductors, and insulators, and can manifest correlated phases such as superconductivity, charge density waves, and magnetism. An ongoing challenge in the field is to incorporate these 2D materials into multilayer heterostructures with robust electrical contacts while preventing disorder and degradation. In particular, preserving and studying air-sensitive 2D materials has presented a significant challenge since they readily oxidize under atmospheric conditions. We report a new technique for contacting 2D materials, in which metal <I>via contacts</I> are integrated into flakes of insulating hexagonal boron nitride, and then placed onto the desired conducting 2D layer, avoiding direct lithographic patterning onto the 2D conductor. The metal contacts are planar with the bottom surface of the boron nitride and form robust contacts to multiple 2D materials. These structures protect air-sensitive 2D materials for months with no degradation in performance. This via contact technique will provide the capability to produce “atomic printed circuit boards” that can form the basis of more complex multilayer heterostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2018/nalefd.2018.18.issue-2/acs.nanolett.7b05161/production/images/medium/nl-2017-05161z_0005.gif'></P>