On the Prediction of Damping and Vibratory Behaviour of Free-Free Multilayered Conical Shells

An analysis is presented for the prediction of resonance frequencies and the associated system loss factors for all families of modes of vibrations in free-free multilayered conical shells, which are frequently used in aircraft, missiles and other allied systems. Because of the spin of a high order, missiles and gun-launched shells are subjected to torsional vibrations (Axisymmetric). The governing equations of motion for the axisymmetric vibrations of a general multilayered conical shell have been derived using Hamilton's vibrational principle. The solution is obtained by utilising simple trignometric series modal assumptions in Galerkin's procedure. The Correspondence principle of linear viscoelasticity for harmonic motions is used for evaluating the damping effectiveness of shells with elastic and viscoelastic layers. The resonance frequencies and the associated system loss factors for three-, five-and seven-layered conical shells with free edges are evaluated and their variations with geometric parameters are investigated. An increase in the number of layers (N) increases maximum obtainable ( system loss factor) for most of the modes with proper selection of geometric parameters, but increasing N beyond 5 yields only marginal increase in (system loss factor). Uniformly high values of (system loss factor) are obtained for all modes of vibration for high values of thickness ratio parameter. For thick shells, more layers are advisable for relatively high values of (system loss factor) for all modes

Concomitant use of isotretinoin and lasers with implications for future guidelines: An updated systematic review

It is generally believed that intervention on skin while on isotretinoin or within 6 to 12 months after treatment can lead to prolonged healing and abnormal scarring. The objective of this systematic review is to evaluate the body of evidence on concomitant use of isotretinoin and lasers for adverse events as a consequence of treatment. A PRISMA‐compliant systematic review (Systematic Review Registration Number: CRD42017056492) of 12 electronic databases was conducted for the terms “laser” and “isotretinoin” or associated brand names from inception until June 2020. Subsequent reference search of studies meeting predefined inclusion criteria were conducted, and all articles were evaluated for bias and assigned levels of evidence to facilitate data synthesis. The search strategy produced 29 studies. Of 871 patients included in the studies of interest, 12 experienced transient adverse effects that resolved spontaneously, and only two presented with keloid formation, both from case reports. This systematic review suggests the risk associated with concomitant isotretinoin and laser use is small to absent. Further studies are needed, but these results suggest that current contraindications may be overly cautious.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163929/1/dth14022.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163929/2/dth14022_am.pd

Climate change impacts on WASH and slum community-based adaptation measures

As with all climatic events, impact of climate change affects urban poor communities the hardest. Often the most vulnerable in terms of their limited access to safe water and hygienic sanitation as well as the vulnerable location of their homes and limited resources to cope with emergencies. This study attempted to access the vulnerability of squatter households in the Kathmandu valley to climate change, specifically on their water and sanitation situation as well as learn on adaptation measures adopted by urban poor.30 households of Pathivara Informal Settlement were interviewed to understand the perception of climate change. The community has already adopted self-adaptation practices such as increased rain water harvesting, water treatment, use of public toilet, reuse of grey water to cope with climate. The findings of this study are useful to advocate for climate resilient urban planning and to encourage other urban poor communities to cope with climate change impact

Utilization of fish trash for increasing yield and quality of milk in cattle

The difference between cost of milk production and Its telling price Is very thin and Is getting thinner due to cumulative increase in cattle food prices on one side and limitations on marketing price of milk on the other. Possible utilization of trash fish converted to liquid silage a* a part of cattle food resulting In Increased yield of milk and fat concern are discussed in this paper. The development of silage and field trials on milking catties were carried out by Gujarat Fisheries Aquatic Sciences Research Institute, Okha

Barriers to the practice of exclusive breastfeeding among HIV-positive mothers in sub-Saharan Africa: A scoping review of counselling, socioeconomic and cultural factors

The World Health Organization (WHO) recommends exclusive breast-feeding (EBF) for HIV exposed infants for six months; this is considered best practice for reducing mother-to-child transmission of HIV in the postpartum period. This is a scoping review of the barriers affecting women's decision-making and choice to sustain the practice of EBF in sub-Saharan Africa (SSA). An online literature search via PubMed, Science Direct, Google Scholar, WHO and Joint United Nations programme on HIV and AIDS (UNAIDS) websites identified research studies and reports that explored socio-economic, cultural and infant feeding counselling-related barriers to EBF among HIV-positive mothers in SSA. A total of 341 relevant articles were identified only 35 (23 qualitative, 3 quantitative and 9 mixed methods) met the inclusion criteria. Findings reveal that key barriers to choice and sustained practice of EBF are healthcare workers’ personal biases, inadequate counselling skills and guideline knowledge, a culture of mixed feeding norms, and maternal lack of decision-making power and fear of vertical transmission. Transmission of HIV programs in countries where major challenges persist should evaluate and address the identified healthcare worker and community-level factors impeding EBF

Cosmic (super)string constraints from 21 cm radiation

We calculate the contribution of cosmic strings arising from a phase transition in the early universe, or cosmic superstrings arising from brane inflation, to the cosmic 21 cm power spectrum at redshifts z > 30. Future experiments can exploit this effect to constrain the cosmic string tension Gu and probe virtually the entire brane inflation model space allowed by current observations. Although current experiments with a collecting area of ~ 1 km^2 will not provide any useful constraints, future experiments with a collecting area of 10^4-10^6 km^2 covering the cleanest 10% of the sky can in principle constrain cosmic strings with tension Gu > 10^(-10) to 10^(-12) (superstring/phase transition mass scale >10^13 GeV).Comment: Accepted for publication in PR

Shear Strength Behaviour of Clay Reinforced with Treated Coir Fibres

The effect of treated coir fibres on the shear strength behaviour of clay is presented in this study. A series of consolidated undrained test were performed on soil reinforced with untreated, sodium hydroxide treated and carbon tetrachloride treated fibres. The coir fibre content was varied from 0.4% to 1.6%. The results indicated that the deviator stress at failure of the clay and clay with untreated coir fibres can be increased by treatment with carbon tetrachloride and sodium hydroxide. A significant increase was also observed in shear strength parameters of clay reinforced with coir fibres at different percentages. The two parameter dependent hyperbolic models were used for predicting the experimental results. The back predicted stressstrain curve at dierent fibre percentage was found to compare well with the experimental results. The clay reinforced with untreated/treated coir fibres has shown improved strength behaviour, it can be used for short term stability problems

Surface Defect incorporated Diamond Machining of Silicon

This paper reports the performance enhancement benefits in diamond turning of the silicon wafer by incorporation of the Surface Defect Machining (SDM) method. The hybrid micromachining methods usually require additional hardware to leverage the added advantage of hybrid technologies such as laser heating, cryogenic cooling, electric pulse or ultrasonic elliptical vibration. The SDM method tested in this paper does not require any such additional baggage and is easy to implement in a sequential micro-machining mode. This paper made use of Raman spectroscopy data, average surface roughness data and imaging data of the cutting chips of silicon for drawing a comparison between conventional Single Point Diamond Turning (SPDT) and SDM while incorporating surface defects in the (i) circumferential and (ii) radial directions. Complimentary 3D Finite Element Analysis (FEA) was performed to analyse the cutting forces and the evolution of residual stress on the machined wafer. It was found that the surface defects generated in the circumferential direction with an interspacing of 1 mm revealed the lowest average surface roughness (Ra) of 3.2 nm as opposed to 8 nm Ra obtained through conventional SPDT using the same cutting parameters. The observation of the Raman spectroscopy performed on the cutting chips showed remnants of phase transformation during the micromachining process in all cases. FEA was used to extract quantifiable information about the residual stress as well as the sub-surface integrity and it was discovered that the grooves made in the circumferential direction gave the best machining performance. The information being reported here is expected to provide an avalanche of opportunities in the SPDT area for low-cost machining solution for a range of other nominal hard, brittle materials such as SiC, ZnSe and GaAs as well as hard steels