Charge Density Wave Order in the Topological Insulator Bi2Se3Bi_2Se_3

Hexagonally deformed Fermi surfaces and strong nesting, found in topological insulators (TIs) such as $Bi_2Se_3$ and $Bi_2Te_3$ over the past decade, have led to several predictions of possible Density Wave order in these systems. Recent evidence for strong Fermi nesting in superconducting $Cu-Bi_2Se_3$ and $Nb-Bi_2Se_3$ has led to further speculation about the importance of charge order in the context of unconventional superconductivity. Here, we report what we believe is the first direct observation of Charge Density Wave (CDW) order in $Bi_2Se_3$. Our results include the observation of a 140K metal-insulator-metal transition in resistivity as a function of temperature. We corroborate this with nuclear magnetic resonance (NMR) studies of the spin-lattice relaxation $\frac{1}{T_1}$ rate of the $^{209}Bi$ nucleus, which also displays a transition at 140K. Additionally, we use electron diffraction to reveal a periodic lattice distortion (PLD) in $Bi_2Se_3$, together with diffuse charge order between $\vec{k}$ and $\vec{k} \pm \Delta\vec{k}$. This diffuse scattering points toward the presence of an incommensurate charge density wave (I-CDW) above room temperature, which locks into a CDW upon cooling below $\sim140K$. We also observe two additional transitions in $\frac{1}{T_1}$ near 200K and 15K. The transition at 200K appears to display some anisotropy with the direction of applied magnetic field. In this report, we focus on the CDW transition at 140K. We include some speculation of the two other transitions observed at 15K and 200K by NMR, also revealed here for the first time.Comment: 16 pages, 5 figure

Evaluation of Preclinical Task Based Learning program in Medical Education [version 1; peer review: 1 approved, 2 approved with reservations]

The conventional curriculum in preclinical medical education has a need for early clinical exposure programs that help in correlation of basic science data with clinical skills. This is helpful to develop clinical reasoning skills, problem-solving abilities, team work, communication skills and overall attitudes and behaviour relevant for a healthcare provider. Preclinical task based learning (TskBL) is an active learning strategy in which the focus for the first year medical student is a real task done by a doctor. In this strategy the student-doctors undergo a standardized patient encounter and discuss the learning issues related to the task in the first year of medical school. The current study is focussed on the student perception of the effectiveness of task based learning module.The TskBL was conducted among first year medical students for nine topics that are commonly encountered in the clinics. After TskBL was planned and implemented the evaluation of the modules was done using focus group discussions. The students highlighted the importance of standardized patients in the TskBL strategy in providing early clinical exposure in preclinical medical education. They reported its usefulness gaining essential knowledge, skills and attitudes for medical learning. They reported positive outcomes of module design and processes and activities in TskBL. Based on the negative aspects of the modules, future improvement was suggested in improving the usefulness of standardized patient encounter. This study showed the novice learners’ outlook of the potency of TskBL for several other topics of clinical relevance to provide early clinical exposure in medical schools

Residual life estimation of structural beam using experimental and numerical modal analysis methods

A structural beam is a common element in many mechanical structures such as ship propeller shaft, crane boom, and aircraft wings. In the present paper experimental and numerical modal analysis are carried out for estimating the damage, geometric location of the damage, severity of damage and residual life of structural beam to prevent unexpected failures of mechanical structures. Experimental and numerical modal analysis results for healthy and cracked beam are compared for validation of numerical methodology used in the present paper. Experimental modal analysis is performed on both healthy and cracked beam with the help of impact hammer, acceleration sensor and FFT (Fast Fourier Transformer) analyzer associated with EDM (Engineering Data Management) software. Modal tests are conducted using impact method on selected locations of the entire healthy and cracked beam to find the first three natural frequencies, which are used to detect the presence of damage and geometric location of the damage. Three parametric studies are carried out to know the effect of crack depth, crack location and crack orientation on the natural frequencies of the cracked beam. Finally, the residual life of a healthy and cracked beam was estimated using Basiquin’s equation and finite element analysis software called ANSYS 18.1

Modified RURS' elbow guard: An extraoral appliance for the digit sucking habit

Digit sucking is the most common oral fixation seen in children. Some situations that stimulate digit sucking are fatigue, boredom, excitement, hunger, fear, physical, and emotional stress. If these habits persist beyond the preschool age when permanent teeth start to erupt, they may be implicated as an important environmental etiological factor associated with the development of malocclusion. This article presents a case report of a 9-year-old female patient with thumb sucking habit since childhood and describes the steps in the fabrication of the modified RURS' elbow guard appliance for more efficient function

Codon Optimization of the Tat Antigen of Human Immunodeficiency Virus Type 1 Generates Strong Immune Responses in Mice following Genetic Immunization

DNA vaccines have been successful in eliciting potent immune responses in mice. Their efficiency, however, is restricted in larger animals. One reason for the limited performance of the DNA vaccines is the lack of molecular strategies to enhance immune responses. Additionally, genes directly cloned from pathogenic organisms may not be efficiently translated in a heterologous host expression system as a consequence of codon bias. To evaluate the influence of codon optimization on the immune response, we elected to use the Tat antigens of human immunodeficiency virus type 1 (HIV-1) (subtype C) and HIV-2, as these viral antigens are poorly immunogenic in natural infection and in experimental immunization and they are functionally important in viral infectivity and pathogenesis. Substituting codons that are optimally used in the mammalian system, we synthetically assembled Tat genes and compared them with the wild-type counterparts in two different mouse strains. Codon-optimized Tat genes induced qualitatively and quantitatively superior immune responses as measured in a T-cell proliferation assay, enzyme-linked immunospot assay, and chromium release assay. Importantly, while the wild-type genes promoted a mixed Th1-Th2-type cytokine profile, the codon-optimized genes induced a predominantly Th1 profile. Using a pepscan strategy, we mapped an immunodominant T-helper epitope to the core and basic domains of HIV-1 Tat. We also identified cross-clade immune responses between HIV-1 subtype B and C Tat proteins mapped to this T-helper epitope. Developing molecular strategies to optimize the immunogenicity of DNA vaccines is critical for inducing strong immune responses, especially to antigens like Tat. Our identification of a highly conserved T-helper epitope in the first exon of HIV-1 Tat of subtype C and the demonstration of a cross-clade immune response between subtypes B and C are important for a more rational design of an HIV vaccine

Prevalence of bronchial asthma among school-going children in Mangalore, South India

Background: Asthma in childhood is a major public health issue. Objective: To estimate prevalence and associated housing environment factors of asthma among school children. Material & Methods: We conducted a cross sectional study among school children aged six to fifteen years. Standard ISAAC (International Study of Asthma and Allergies in Children) Core Questionnaire for Asthma was used for determining the prevalence of wheezing and asthma. Demographic, housing and indoor pollution factors were collected. Data were analyzed by SPSS version 15. Results: Prevalence of ‘wheeze ever’ and ‘current wheezers’ was 10% and 9% respectively.  Physician diagnosed asthma was seen in 6.3 %. Severe asthma was noted in 28.6% of current wheezerswith 84.6% and 8.8% having one to two and four to 12 wheezing attacks per year respectively. Wheezing was present post exercise in 5.4%, nocturnal cough in 6.1%, sleep disturbance less than one night/week (40.7%), one or more nights/week (3.3%) and wheezing limiting speech to few words between breaths (20.9%). Prevalence was greater among boys (9.8%) than girls (7.5%) and maximal in age group eight to nine years. On multiple logistic regression presence of overcrowding and absence of smoke outlet were significantly associated with current wheeze. Socio-economic status, beedi rolling practices and absence of separate kitchen was statistically significant with severe asthma. Conclusions: Current wheezer prevalence was9% and more in boys. Adoption of improved housing conditions and avoiding environmental tobacco exposure may aid in reducing childhood asthma attacks in this developing city