Nanoscale aggregation phenomena at the contact line of air-drying pure water droplets on silicon revealed by atomic force microscopy

A. Méndez-Vilas,A.B. Jódar-Reyes,J. Díaz,M.L. González-Martín 한국물리학회 2009 Current Applied Physics Vol.9 No.1

In the present work, silicon wafer surfaces were studied during a pure water dewetting process in ambient conditions by intermittentcontact atomic force microscopy (AFM). With an acid-free surface cleaning, large network structures of tens of microns in extension but only a few nanometers in height were observed, being stable for days. Fractal-like assemblies have been previously reported in a variety of different scenarios, for example, when an aqueous solution of carbon-based species, especially carbon nanotubes, is left to evaporate on a solid substrate, provided that no complete wetting was produced. Chemical mapping of silicon wafer surfaces, while unable to provide a spatial resolution comparable to that of the AFM, clearly showed the initially formed contact line to be enriched in carbon. Therefore, hydrophobic and/or non-soluble (or slightly soluble) substances which are present on every surface exposed to air are expected to be responsible for the observed fractal structures. Reactions of the network structures toward changing environmental conditions were analyzed. When increasing the ambient humidity, the structures grew only slightly, which is indicative of their highly (but not totally) hydrophobic nature. Heating the sample above 100 ℃ for about 10 h led to an almost complete disappearance of these nanostructures. Due to the lateral extension of these stable network heterogeneities, they are expected to affect contact angle measurements in wetting studies, especially at the micro- and nanoscale. When acid-cleaned wafers are used as substrate, deposited water extends as a film over the silicon surface without droplet formation. No fractal structures are then observed. In the present work, silicon wafer surfaces were studied during a pure water dewetting process in ambient conditions by intermittentcontact atomic force microscopy (AFM). With an acid-free surface cleaning, large network structures of tens of microns in extension but only a few nanometers in height were observed, being stable for days. Fractal-like assemblies have been previously reported in a variety of different scenarios, for example, when an aqueous solution of carbon-based species, especially carbon nanotubes, is left to evaporate on a solid substrate, provided that no complete wetting was produced. Chemical mapping of silicon wafer surfaces, while unable to provide a spatial resolution comparable to that of the AFM, clearly showed the initially formed contact line to be enriched in carbon. Therefore, hydrophobic and/or non-soluble (or slightly soluble) substances which are present on every surface exposed to air are expected to be responsible for the observed fractal structures. Reactions of the network structures toward changing environmental conditions were analyzed. When increasing the ambient humidity, the structures grew only slightly, which is indicative of their highly (but not totally) hydrophobic nature. Heating the sample above 100 ℃ for about 10 h led to an almost complete disappearance of these nanostructures. Due to the lateral extension of these stable network heterogeneities, they are expected to affect contact angle measurements in wetting studies, especially at the micro- and nanoscale. When acid-cleaned wafers are used as substrate, deposited water extends as a film over the silicon surface without droplet formation. No fractal structures are then observed.

Rehabilitation of a distressed steel roof truss - A study

M.A. Dar,N. Subramanian,A.R. Dar,J. Raju 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.5

Structural failures are undesirable events that devastate the construction industry resulting in loss of life, injury, huge property loss, and also affect the economy of the region. Roof truss failures occur mainly due to excessive loading, improper fabrication, deterioration, inadequate repair, etc. Although very rare, a roof truss may even fail due to inappropriate location of supports. One such case was reported from the recent failure of a steel roof truss used in an indoor stadium at Kargil in India. Kargil region, being mountainous in nature, receives heavy snowfall and hence the steel roof trusses are designed for heavy snow loads. Due to inappropriate support location, the indoor stadium’s steel roof truss had failed under heavy snow load for which it was designed and became an interesting structural engineering problem. The failure observed was primarily in terms of yielding of the bottom chord under the supports, leading to partial collapse of the roof truss. This paper summarizes the results of laboratory tests and analytical studies that focused on the validation of the proposed remedial measure for rehabilitating this distressed steel roof truss. The study presents the evaluation of (i) significant reduction in strength and stiffness of the distressed truss resulting in its failure, (ii) desired recovery in both strength and stiffness of the rectified truss contributed by the proposed remedial measure. Three types of models i.e., ideal truss model, as build truss model and rectified truss model were fabricated and tested under monotonic loading. The structural configuration and support condition varied in all the three models to represent the ideal truss, distressed truss and the rectified truss. To verify the accuracy of the experimental results, an analytical study was carried out and the results of this analytical study are compared with the experimental ones.

Self-assembled Co₃O₄ nanoplatelets into micro-spheres via a simple solvothermal route: Structural and electrochemical properties

Dar, M.A.,Nam, S.H.,Abdo, H.S.,Almajid, A.A.,Kim, D.W.,Qurashi, A.,Kim, W.B. Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.695 No.-

<P><B>Abstract</B></P> <P>The self-assembled Co<SUB>3</SUB>O<SUB>4</SUB> microspheres made of nanoplatelets were prepared by a novel and simple solvothermal route. The crystal structure and morphology were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The FESEM shows that the average diameter of the microspheres is about 8 μm and the thickness of individual nanoplatelets is 30–70 nm. X-ray photoelectron spectroscopy (XPS) studies reveal two strong peaks appearing at 780.6 and 797.0 eV, corresponding to the core level electrons for Co 2p<SUB>3/2</SUB> and Co 2p<SUB>1/2</SUB>, which are characteristic XPS peaks of Co<SUB>3</SUB>O<SUB>4</SUB> phase. The electrochemical properties of cobalt oxide nanoplatelets modified electrodes were scrutinized by cyclic voltammetry (CV) and charge-discharge profile with cycles, showing a stable reversible capacity of 620 mA h/g after 40 cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of self-assembled Co<SUB>3</SUB>O<SUB>4</SUB> nanoplatelets via a simple solvothermal route. </LI> <LI> XPS studies reveals the two peaks, corresponding to the core level electrons of Co 2p<SUB>3/2</SUB> and Co 2p<SUB>1/2</SUB>. </LI> <LI> Co<SUB>3</SUB>O<SUB>4</SUB> anode in Li-ion batteries showed a reversible capacity of 620 mA h/g after 40 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

PHA-Induced Peripheral Blood Cytogenetics and Molecular Anslysis : a Valid Diagnostic and Follow-up Modality For Acute Primyelocytic Leukemia Patients Treated With ATRA and/or Arsenic Tri-oxide

Baba, Shahid M,Azad, Niyaz A,Shah, Zaffar A,Afroze, Dil,Pandith, Arshad A,Jan, Aleem,Aziz, Sheikh A,Dar, Fayaz A Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.4

Background: Acute promyelocytic leukemia (APML) is characterized by the reciprocal translocation t(15;17) (p22;p12) resulting in the PML-$RAR{\alpha}$ fusion gene. A dual diagnostic and follow up approach was applied including cytogenetic demonstration of the t(15;17) translocation and detection dg PML-$RAR{\alpha}$ chimeric transcripts by molecular means. Purpose: Conventional cytogenetics involving bone marrow is beset with high probability of poor metaphase index and was substituted with phytohemagglutinin (PHA)-induced peripheral blood culture based cytogenetic analysis as a diagnostic & follow up modality in APML patients of Kashmir (North India). Both qualitative (RT-PCR) and quantitative (Q-PCR) tests were simultaneously carried out to authenticte the modified cytogenetics. Materials and Method: Patient samples were subjected to the said techniques to establish their baseline as well as follow-up status. Results: Initial cytogenetics revealed 30 patients (81%) Positive for t(15;17) whereas 7 (19%) had either cryptic translocation or were negative for t(15;17). Two cases had chromosome 16q deletion and no hallmark translocation t(15;17). Q-PCR status for PML-$RAR{\alpha}$ was found to be positive for all patients. All the APML patients were reassessed at the end of consolidation phase and during maintenance phase of chemotherapy where 6 patients had molecular relapse, wherein 4 also demonstrated cytogenetic relapse. Conclusions: It was found that PHA-induced peripheral blood cytogenetics along with molecular analysis could prove a reliable modality in the diagnosis and assessment of follow up response of APML patients.

Psychiatric Co-morbidity in Patients With Irritable Bowel Syndrome at a Tertiary Care Center in Northern India

( Yuman Kawoos ),( Zaid A Wani ),( Showkat A Kadla ),( Irfan A Shah ),( Arshad Hussain ),( M Maqbool Dar ),( Mushtaq A Margoob ),( Kouser Sideeq ) 대한소화기기능성질환·운동학회(구 대한소화관운동학회) 2017 Journal of Neurogastroenterology and Motility (JNM Vol.23 No.4

Background/Aims Irritable bowel syndrome (IBS) is a chronic psycho-physiological disorder. It is considered to be the most common functional gastrointestinal disorder, and about 50-90% of IBS patients have associated psychiatric co-morbidity. We aimed to study psychiatric co-morbidities in patients with IBS visiting a tertiary care center. Methods This was a cross-sectional case-control study conducted over a duration of one and a half years from January 2014 to July 2015. Patients were selected from the out-patient department of gastroenterology. About 160 patients with IBS who fulfilled the inclusion criteria and who gave written informed consent were selected as study cases. The healthy attendants of cases were selected as controls. A total of 200 controls were selected. Rome-III criteria were used to diagnose IBS. For diagnosing psychiatric disorders, we used the Mini International Neuropsychiatric Interview Schedule Plus. Results Mean age of our cases and controls was 39.7 ± 11.4 and 37.7 ± 9.6 years, respectively. Females outnumbered males in our cases as well as their controls by a ratio of 2:1 approximately. Psychiatric disorders were seen in 84.4% of IBS patients as compared to 41.5% in controls. Major psychiatric disorders seen in our patients were generalized anxiety disorders (30.0%) and depression (28.0%). Conclusions The majority of patients with IBS who present to a tertiary care center have co-morbid psychiatric disorders. We need to screen these patients for such co-morbidities and develop a holistic approach for better outcome in such cases. (J Neurogastroenterol Motil 2017;23:555-560)

Structural performance of cold-formed steel composite beams

M. Adil Dar,N. Subramanian,M. Anbarasu,A.R. Dar,James B.P. Lim 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.5

This study presents a novel method of improving the strength and stiffness of cold-formed steel (CFS) beams. Flexural members are primary members in most of the structures. Hence, there is an urgent need in the CFS industry to look beyond the conventional CFS beam sections and develop novel techniques to address the severe local buckling problems that exist in CFS flexural members. The primary objective of this study was to develop new CFS composite beam sections with improved structural performance and economy. This paper presents an experimental study conducted on different CFS composite beams with simply supported end conditions under four point loading. Material properties and geometric imperfections of the models were measured. The test strengths of the models are compared with the design strengths predicted by using Australian/New Zealand Standard for cold-formed steel structures. Furthermore, to ensure high precision testing, a special testing rig was also developed for testing of long span beams. The description of test models, testing rig features and test results are presented here. For better interpretation of results, a comparison of the test results with a hot rolled section is also presented. The test results have shown that the proposed CFS composite beams are promising both in terms of better structural performance as well as economy.

Experimental study on innovative sections for cold formed steel beams

M.A. Dar,M. Yusuf,A.R. Dar,J. Raju 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.6

Cold Formed Steel members are widely used in today&'s construction industry. However the structural behavior of light gauge high strength cold formed steel sections characterized by various buckling modes are not yet fully understood. Because of their simple forming and easy connections, the commonly used cold formed sections for beams are C and Z. However both these sections suffer from certain buckling modes. To achieve much improved structural performance of cold formed sections for beams both in terms of strength and stiffness, it is important to either delay or completely eliminate their various modes of buckling. This paper presents various innovative sectional profiles and stiffening arrangements for cold formed steel beams which would successfully contribute in delaying or eliminating various modes of premature buckling, thus considerably improving the load carrying capacity as well as stiffness characteristics of such innovative cold formed sections compared to conventional cold formed steel sections commonly used for beams.

Effect of angle stiffeners on the flexural strength and stiffness of cold-formed steel beams

M. Adil Dar,N. Subramanian,Amer I. Rather,A.R. Dar,James B. P. Lim,M. Anbarasu,Krishanu Roy 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.2

Cold-formed steel (CFS) sections when used as primary load carrying members often require additional strengthening for retrofitting purposes. In some cases, it is also necessary to reduce deflections in order to satisfy serviceability requirements. The introduction of angle sections, screwed to the webs so as to act as external stiffeners, has the potential to both increase flexural strength as well as reduce deflections. This paper presents the results of ten four-point bending tests, on built-up CFS sections, both open and closed, with different stiffening arrangements. In the laboratory tests, the stiffening arrangements increased the moment capacity and stiffness of the CFS beams by up to 85% and 100% respectively. The increase in moment capacity was more evident for the open sections, while that reduction in deflection was largest for the closed sections.

Flexural Strength of cold-formed steel built-up composite beams with rectangular compression flanges

M. Adil Dar,N. Subramanian,Dawood A. Dar,A.R. Dar,M. Anbarasu,James B. P. Lim,Soroush Mahjoubi 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.2

The past research on cold-formed steel (CFS) flexural members have proved that rectangular hollow flanged sections perform better than conventional I-sections due to their higher torsional rigidity over the later ones. However, CFS members are vulnerable to local buckling, substantially due to their thin-walled features. The use of packing, such as firmly connected timber planks, to the flanges of conventional CFS lipped I-sections can drastically improve their flexural performance as well as structural efficiency. Whilst several CFS composites have been developed so far, only limited packing materials have been tried. This paper presents a series of tests carried out on different rectangular hollow compression flanged sections with innovative packing materials. Four-point flexural tests were carried out to assess the flexural capacity, failure modes and deformed shapes of the CFS composite beam specimens. The geometric imperfections were measured and reported. The North American Specifications and Indian Standard for cold-formed steel structures were used to compare the design strengths of the experimental specimen. The test results indicate clearly that CFS rectangular ‘compression’ flanged composite beams perform significantly better than the conventional rectangular hollow flanged CFS sections.

Stiffening schemes for CFS built-up I-beams with large global imperfections: Capacity and behaviour

M. Adil Dar,M. Anbarasu,A.R. Dar,Naqeeb Ul Islam,Ahmad Fayeq Ghowsi,Hermes Carvalho 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.4

Cold-formed steel (CFS) sections are thin-walled, therefore, more susceptible to different types of geometric imperfections. Global type of geometric imperfections has a significant impact on the load-carrying capacity of flexural members. This paper reports an experimental study that discusses the influence of global imperfections on the flexural response of CFS built-up I-beams composed of two lipped channels, with simply supported ends, under four-point loading. Global imperfections of magnitude over eight times the maximum permissible ones were induced in the specimens, leading to their distress. Using various simple stiffening schemes, the capacity and stiffness of the distressed specimens were improvised. The performance comparisons were made based on the maximum loads resisted, flexural stiffnesses offered, and failure modes experienced by the specimens. As experimental data on such distressed specimens are currently lacking in the literature, the test results of the present study will provide the necessary data needed by future researchers to numerically extend this study further, which will help in the development of necessary design guidelines for the same. The stiffening schemes significantly improved the structural efficiency of distressed specimens in terms of strength and stiffness, by over 60%. As a result, an effective and time-saving solution to such realistic structural engineering problems is given.