UBVI CCD Photometry of the Open Cluster NGC 4609 and Hogg 15

UBVI CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V) = 0.37 +/- 0.03, V_0 - M_V = 10.60 +/- 0.08, log tau = 7.7 +/- 0.1; Hogg 15 : E(B-V) = 1.13 +/- 0.11, V_0 - M_V = 12.50 +/- 0.15, log tau <= 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We have also determined the mass function of these clusters and have obtained a normal slope (Gamma = -1.2 +/- 0.3) for NGC 4609 and a somewhat shallow slope (Gamma = -0.95 +/- 0.5) for Hogg 15.Comment: 12 pages, 14 figures, JKAS, in pres

Critical flux-based membrane fouling control of forward osmosis: Behavior, sustainability, and reversibility

Membrane fouling is closely related to the concept of critical flux. Therefore, a fouling control strategy for forward osmosis (FO) membranes that is based on the critical flux is necessary. This study systematically investigated the critical flux behavior of FO membranes (CTA and PA-TFC) in the short-term using a stepping method (draw solution (DS) concentration stepping). In addition, to test the reliability of this method, long-term experiments were conducted to evaluate the influences of operational critical flux on the fouling behavior (sustainable operation and fouling reversibility/irreversibility), thereby determining the critical flux for reversibility. Our results showed that the DS concentration stepping could be applied for critical flux determination in FO. Both membranes exhibited higher critical flux values for alginate fouling compared to other single foulants such as colloidal silica or gypsum. The values were 15.9 LMH for a cellulose triacetate membrane (CTA) and 20.5 LMH for the polyamide thin-film composite (PA-TFC). Whilst these values should be adequate in FO applications they were determined for single foulants. The presence of multispecies of foulants caused a significant decline in the critical flux values. This study found 5.4 LMH for the CTA membrane and 8.3 LMH for the PA-TFC membrane for the combined foulants of alginate + gypsum. This indicates that the critical flux behavior in FO was dependent on the foulant type and membrane type. Importantly, the high restoration of water flux was achieved with the PA-TFC membrane at an operation either close to critical flux (92–98%) or below critical flux (98–100%) (i.e., with negligible irreversible fouling). The critical fluxes for reversibility obtained in this study will aid the efficient operation of practical FO processes

Understanding the Unique Electronic Properties of Nano Structures Using Photoemission Theory

Newly emerging experimental techniques such as nano-ARPES are expected to provide an opportunity to measure the electronic properties of nano-materials directly. However, the interpretation of the spectra is not simple because it must consider quantum mechanical effects related to the measurement process itself. Here, we demonstrate a novel approach that can overcome this problem by using an adequate simulation to corroborate the experimental results. Ab initio calculation on arbitrarily-shaped or chemically ornamented nano-structures is elaborately correlated to photoemission theory. This correlation can be directly exploited to interpret the experimental results. To test this method, a direct comparison was made between the calculation results and experimental results on highly-oriented pyrolytic graphite (HOPG). As a general extension, the unique electronic structures of nano-sized graphene oxide and features from the experimental result of black phosphorous (BP) are disclosed for the first time as supportive evidence of the usefulness of this method. This work pioneers an approach to intuitive and practical understanding of the electronic properties of nano-materials.11Ysciescopu

Efficiently Sampling the PSD Cone with the Metric Dikin Walk

Semi-definite programs represent a frontier of efficient computation. While there has been much progress on semi-definite optimization, with moderate-sized instances currently solvable in practice by the interior-point method, the basic problem of sampling semi-definite solutions remains a formidable challenge. The direct application of known polynomial-time algorithms for sampling general convex bodies to semi-definite sampling leads to a prohibitively high running time. In addition, known general methods require an expensive rounding phase as pre-processing. Here we analyze the Dikin walk, by first adapting it to general metrics, then devising suitable metrics for the PSD cone with affine constraints. The resulting mixing time and per-step complexity are considerably smaller, and by an appropriate choice of the metric, the dependence on the number of constraints can be made polylogarithmic. We introduce a refined notion of self-concordant matrix functions and give rules for combining different metrics. Along the way, we further develop the theory of interior-point methods for sampling.Comment: 54 page

Steadily Increasing Star Formation Rates in Galaxies Observed at 3 <~ z <~ 5 in the CANDELS/GOODS-S Field

We investigate the star formation histories (SFHs) of high redshift (3 <~ z <~ 5) star-forming galaxies selected based on their rest-frame ultraviolet (UV) colors in the CANDELS/GOODS-S field. By comparing the results from the spectral-energy-distribution-fitting analysis with two different assumptions about the SFHs --- i.e., exponentially declining SFHs as well as increasing ones, we conclude that the SFHs of high-redshift star-forming galaxies increase with time rather than exponentially decline. We also examine the correlations between the star formation rates (SFRs) and the stellar masses. When the galaxies are fit with rising SFRs, we find that the trend seen in the data qualitatively matches the expectations from a semi-analytic model of galaxy formation. The mean specific SFR is shown to increase with redshift, also in agreement with the theoretical prediction. From the derived tight correlation between stellar masses and SFRs, we derive the mean SFH of star-forming galaxies in the redshift range of 3 <~ z <~ 5, which shows a steep power-law (with power alpha = 5.85) increase with time. We also investigate the formation timescales and the mean stellar population ages of these star-forming galaxies. Our analysis reveals that UV-selected star-forming galaxies have a broad range of the formation redshift. The derived stellar masses and the stellar population ages show positive correlation in a sense that more massive galaxies are on average older, but with significant scatter. This large scatter implies that the galaxies' mass is not the only factor which affects the growth or star formation of high-redshift galaxies.Comment: 31 pages, 8 figures, 2 table

On-grid location-by-location variations of transmission electron microscope imaged in-flame soot particles in a small-bore diesel engine

In a small-bore diesel engine, soot particles are sampled directly from the flames by placing a transmission electron microscope (TEM) grid inside the cylinder. The TEM images are taken from multiple on-grid locations to ensure enough number of soot particles are post-processed for statistically meaningful data of morphology parameters. This study presents variations in the soot TEM images and sizes of soot aggregates and primary particles from 30 different on-grid locations for each of jet-wall impingement and jet-jet interaction regions of the diesel flames. The TEM images show significant variations in soot aggregate size and structures for the two different sampling regions with overall larger and more complex soot for the jet-jet interaction region. The statistical results show that the difference in soot primary particle diameter is measurable after five images were processed. For soot aggregate radius of gyration, the two samples show no apparent variations until 25 images were processed, and the mean values levelled only when more than 27 images were processed. As the enough number of TEM images were processed, the larger sizes in both soot aggregates and primary particles were confirmed for the jet-jet interaction region

Near-TDC Flow-Field Analysis in a High-Tumble Production Spark-Ignition Engine Using Endoscopic High-Speed Particle Image Velocimetry

The latest-generation spark-ignition (SI) engines implement high-tumble flow design to achieve unprecedented high brake thermal efficiency of over 40%, which will continue to play an important role in both conventional and future electrified vehicles. To maximize the potential of high-tumble SI engines, there is a clear need for in-cylinder flow and flame analysis conducted timely in a realistic environment. For the first time, this study meets this need by performing innovative endoscopic imaging of flow fields and flame inside the cylinder of a selected production engine using a particle image velocimetry (PIV) laser and high-speed camera system operated at 35 kHz. Through this time-resolved, two-dimensional measurement of the realistic in-cylinder phenomenon, many new findings have been achieved. Regarding the tumble vortex, its center is seen more shifted to the exhaust valve side, which is related to an asymmetric "surging"flow structure formed during the upward motion of the piston in the compression stroke. When the piston approaches the top dead center (TDC), the tumble center is not clearly defined anymore, but a new lateral exhaust-to-intake flow forms as the surging flow bounces back off the exhaust valve side of the pent roof. This wall-guided "bounce-back"flow does not form when the intake valve closure (IVC) is retarded for the realization of the Atkinson Cycle, and thus the surging flow is reduced and peaks at a later timing. The new in-cylinder flow structures observed from the high-tumble engine directly impact the flame development. From the high-speed natural combustion luminosity imaging performed using the same camera endoscope, the flame centroid is found to shift toward the intake valve side, which is consistent with the bounce-back flow direction at the advanced IVC timing

Assessments of Pressure-Based Ignition Delay Measurements of Various Cetane Number Fuels in a Small-Bore Compression Ignition Engine

With the increased use of low ignition quality fuels in advanced compression ignition engines, the extended ignition delay and two-stage ignition behavior shown on the measured in-cylinder pressure profile raise a question about at what point of the pressure trace should be identified as the start of combustion (SOC). Previous studies used numerous methods, but a systematic evaluation is lacking, particularly for low ignition quality fuels used in a small-bore engine. The present study bridges this gap by performing high-speed imaging of OH∗ chemiluminescence in a small-bore optical compression ignition engine, against which various methods of ignition delay calculation are assessed for a correct representation of the start of high-temperature reaction - i.e., the actual SOC. These methods include the SOC defined as the pressure recovery point, zero-crossing point of the peak pressure-rise slope, 50% peak pressure-rise point, peak points of the second-order pressure derivative and the change of apparent heat release rate (aHRR), and 10% heat release point (CA10). Three custom-made fuels with a cetane number of 30, 40, and 51 are used with all the fuel physical properties almost fixed but the cetane number. The results show that the first signals of OH∗ chemiluminescence are measured closest to the pressure recovery point while the other methods return a later SOC or longer ignition delay time. Given that the ambient gas temperature is not fixed but changes during the ignition delay in an engine, a correlation between the ignition delay time and calculated bulk gas temperature is also evaluated for a range of temperature points, including the temperature at the start of fuel injection (SOI), temperature at the SOC, mean temperature during the ignition delay, mean temperature between SOI and the end of injection (EOI), mean temperature between EOI and SOC, and temperature difference between SOI and SOC. A correct correlation is found only with the temperature at SOC and the temperature difference between SOI and SOC