Hydrodynamic and Thermal Analyses of Pool Boiling Data Obtained from Experiments Performed on Flat Horizontal Heaters with Conventional and Nano-Structured Surfaces

Pool boiling phenomena on different types of heater configurations have been explored in the heat transfer literature. Pool boiling experiments on heaters with nanostructured surfaces have gained popularity in contemporary literature for microchip cooling application. The thermal management challenges for cooling of electronic chips have become more acute with decrease in the size for these microchips with concomitant increase in device density and heat flux. Pool boiling is expected to provide appropriate technology solutions to meet these challenges for high heat flux cooling at low temperature differentials. In this study, results obtained from pool boiling experiments were analyzed. The experiments were performed using heaters with plain surfaces (copper and silicon) and nanostructured surfaces (Anodic Aluminum Oxide/AAO). In these experiments, high speed digital image acquisition apparatus was used to record bubble dynamics (nucleation, growth and departure) for both nucleate and film boiling regimes. The videos were used to obtain the bubble diameter at departure, bubble growth rates (bubble height as a function of time) and bubble departure frequency. The objective of these experiments was to explore the change in bubble dynamics for different heater configurations in order to ascertain their role in the observed changes in the values of pool boiling heat flux as a function of wall superheat (i.e., from the boiling curves obtained in these experiments). These experiments were performed for saturated boiling conditions as well as for liquid subcooling of 5 °C and 10 °C. The test fluid was PF-5060 (Manufacturer: 3M Corp.). The experimental apparatus utilized in this study consisted of a visualization chamber, cartridge heaters, power supply, high speed digital data acquisition system and chiller unit. Temperature nanosensors (Thin Film Thermocouples/ TFT) as well as wire bead thermocouples were used for measurement of wall superheat. Micro/ nano-fabrication techniques were utilized in this study for realizing the test surfaces integrated with temperature nanosensors. The data gleaned from these experiments were compiled to obtain a correlation for the optimal heat transfer for different heater surface configurations. Literature review was also performed in this study to compare the experimental results with correlations for bubble dynamics available in the literature. The experimental results for bubble dynamics show that while silicon and copper surfaces have similar values for bubble departure diameter, the variability in the bubble departure frequency values for copper heater experiments were larger than that of silicon heaters. This trend is potentially due to large variation in surface roughness on copper heaters compared to that of silicon wafers (which are single crystal silicon substrates and therefore are atomically smooth at the commencement of the experiments). Heaters with nanostructured surfaces (e.g., for AAO heaters) were observed to yield smaller bubble departure diameters and higher bubble departure frequencies

An epidemiological study of mortality among mothers admitted in a rural tertiary hospital of West Bengal

Background: Maternal mortality reflects the quality of obstetric services given to pregnant women in the community. Objectives: The objectives of this study were to calculate the maternal mortality rate in a teaching institution, to assess the epidemiological aspects of maternal mortality, and to assess the different causes of maternal mortality. Materials and Methods: This was a retrospective study where individual records of all maternal deaths occurring in our hospital during the past 6 years from 2009 to 2014 were studied. The cause of death and the factors which led to death in each individual case were analyzed. Results: A total of 105 maternal deaths occurred during the study period. The mean maternal mortality ratio in the study period was 233/100,000 live births. Most maternal deaths (37.14%) occurred in the age group of 20–24 years, multiparous women (74.28%) and in women from rural areas (70.47%). Most of the women were unbooked or unregistered patients (64.76%), and 40.95% cases were referred cases. Direct causes accounted for 90.47% of maternal deaths whereas 9.52% of maternal deaths were due to indirect causes. Hemorrhage (26.6%) and eclampsia (27.6%) were the major direct causes of maternal deaths. Conclusion: There is scope for improvement as a large proportion of the observed deaths are preventable. Improving the rural health centers, upgrading the referral centers, and proper transport system is the need of the hour

An epidemiological study of mortality among mothers admitted in a rural tertiary hospital of West Bengal

Background: Maternal mortality reflects the quality of obstetric services given to pregnant women in the community. Objectives: The objectives of this study were to calculate the maternal mortality rate in a teaching institution, to assess the epidemiological aspects of maternal mortality, and to assess the different causes of maternal mortality. Materials and Methods: This was a retrospective study where individual records of all maternal deaths occurring in our hospital during the past 6 years from 2009 to 2014 were studied. The cause of death and the factors which led to death in each individual case were analyzed. Results: A total of 105 maternal deaths occurred during the study period. The mean maternal mortality ratio in the study period was 233/100,000 live births. Most maternal deaths (37.14%) occurred in the age group of 20–24 years, multiparous women (74.28%) and in women from rural areas (70.47%). Most of the women were unbooked or unregistered patients (64.76%), and 40.95% cases were referred cases. Direct causes accounted for 90.47% of maternal deaths whereas 9.52% of maternal deaths were due to indirect causes. Hemorrhage (26.6%) and eclampsia (27.6%) were the major direct causes of maternal deaths. Conclusion: There is scope for improvement as a large proportion of the observed deaths are preventable. Improving the rural health centers, upgrading the referral centers, and proper transport system is the need of the hour

Rad26, the Transcription-Coupled Repair Factor in Yeast, Is Required for Removal of Stalled RNA Polymerase-II following UV Irradiation

Transcription coupled nucleotide excision repair (TCR) is a major pathway responsible for removal of helix distorting DNA lesions from transcriptionally active regions of the genome. Rad26, a key factor of the TCR pathway, is known to play a role during early steps of TCR. Here, we show that Rad26-mediated TCR is not absolutely dependent on active transcription elongation in budding yeast. As per our results, RAD26- deleted cells show enhanced UV sensitivity compared to wild type cells under conditions where transcription elongation is inhibited. The increased UV sensitivity observed in RAD26 -deleted cells, however, is not due to reduced expression of the major NER-responsive genes. Interestingly, transcription of the constitutively expressed RPB2 gene is adversely affected in RAD26- deleted cells during UV-induced DNA damage repair. In consonance, chromatin immunoprecipitation analysis showed that unlike in wild type, in RAD26 -deleted cells no significant reduction in RNA polymerase II occupancy occurs during nucleotide excision repair in the transcriptionally active loci like, RPB2 , PYK1 and RPL2B . These results collectively indicate that removal of RNAPII during DNA damage repair following UV irradiation is dependent on Rad26

Expression analyses of NER genes and <i>RPB2</i> gene.

<p>RT–PCR analysis was performed on total RNA isolated from WT and WTΔRad26 cells (<b>A</b>) following treatment without or with 100 J/m² UV radiation, using gene-specific primers, as described in Materials and Methods section; (<b>B</b>) of <i>RPB2</i> gene after 100 J/m² UV irradiation followed by repair incubation for different time periods. For each strain, data represent the mean ±1 SD for three independent experiments.</p

Domain organization of Rad26 protein.

<p>Bioinformatics based studies indicated the Rad26 protein to be composed of primarily three distinct domains. The N-terminal aspartate/glutamate-rich acidic domain; a SNF2 domain having the ATP-binding helicase sub-domain consisting of the ATP-binding pocket and a signature DEGH box; and the C-terminal helicase domain.</p

Sensitivity of cells to transcription elongation inhibitors with or without UV treatment.

<p>Cells of exponentially growing cultures were appropriately diluted and spread on SC plates supplemented with MPA (A) or 6-AU (B) of indicated concentrations without UV irradiation. Similarly grown cells were spread on SC plates supplemented with MPA (C) or 6-AU (D) and subjected to UV doses as indicated. Growth was monitored after 72 h. For each strain, data represent the mean ±1 SD for four independent experiments.</p