Direct Numerical Simulation of 3D Salt Fingers: From Secondary Instability to Chaotic Convection

The amplification and equilibration of three-dimensional salt fingers in unbounded uniform vertical gradients of temperature and salinity is modeled with a Direct Numerical Simulation in a triply periodic computational domain. A fluid dynamics video of the simulation shows that the secondary instability of the fastest growing square-planform finger mode is a combination of the well-known vertical shear instability of two-dimensional fingers [Holyer, 1984] and a new horizontal shear mode.Comment: APS DFD Gallery of Fluid Motion 200

Salt fingers in an unbounded thermocline

Numerical solutions for salt fingers in an unbounded thermocline with uniform overall vertical temperature-salinity gradients are obtained from the Navier-Stokes-Boussinesq equations in a finite computational domain with periodic boundary conditions on the velocity. First we extend previous two-dimensional (2D) heat-salt calculations [Prandtl number Pr = ν/kT = 7 and molecular diffusivity ratio τ = kS/kT = 0.01] for density ratio R = 2; as R decreases we show that the average heat and salt fluxes increase rapidly. Then three-dimensional (3D) calculations for R = 2.0, Pr = 7, and the numerically accessible values of τ = 1/6, 1/12 show that the ratio of these 3D fluxes to the corresponding 2D values [at the same (τ, R, Pr)] is approximately two. This ratio is then extrapolated to τ = 0.01 and multiplied by the directly computed 2D fluxes to obtain a first estimate for the 3D heat-salt fluxes, and for the eddy salt diffusivity (defined in terms of the overall vertical salinity gradient). Since these calculations are for relatively small domains [O (10) finger pairs], we then consider much larger scales, such as will include a slowly varying internal gravity wave. An analytic theory which assumes that the finger flux is given parametrically by the small domain flux laws shows that if a critical number A is exceeded, the wave-strain modulates the finger flux divergence in a way which amplifies the wave. This linear theoretical result is confirmed, and the finite amplitude of the wave is obtained, in a 2D numerical calculation which resolves both waves and fingers. For highly supercritical A (small R) it is shown that the temporally increasing wave shear does not reduce the fluxes until the wave Richardson number drops to ~0.5, whereupon the wave starts to overturn. The onset of density inversions suggests that at later time (not calculated), and in a sufficiently large 3D domain, strong convective turbulence will occur in patches

Solid Liquid Extraction of Phenolic and Flavonoid Compounds from Cotinus coggygria and Concentration by Nanofiltration

Extraction kinetics of polyphenols and flavonoids from plant material and their separation and concentration by nanofiltration were investigated. The kinetics experiments were carried out with Cotinus coggygria. The influence of the extraction solvent on the extraction rate was defined. Four different extraction solvents or mixtures were applied – methanol, azeotropic ethanol, 50/50 ethanol/water mixture, and pure water. The optimum extraction rate of flavonoids and polyphenols was achieved by using 50 % ethanol as a solvent for extraction. This solvent mixture was used for generating extracts for the nanofiltration experiments. Organic solvent nanofiltration membranes from DuraMemTM series with different pore sizes (200, 300 500 and 900 Da) were tested in dead-end and cross-flow filtration systems. Flux and rejection data were obtained for every membrane type. Very good separation and respectively concentration of the extracted useful compounds was achieved (rejection for polyphenols and flavonoids is 91 and 93 %, respectively). During a feed/extract concentration experiment, the constant polyphenols and flavonoids rejection was measured. The results suggest that the nanofiltration technology could be combined successfully with solid-liquid extraction for natural sourced valuable compounds enrichment

Exploring the feasibility and acceptability of the contents, design, and functionalities of an online intervention promoting mental health, wellbeing, and study skills in Higher Education students

Background: Substantial numbers of students in Higher Education (HE) are reporting mental health difficulties, such as mild to moderate symptoms of depression and anxiety. Coupled with academic skills challenges, these difficulties can lead to decreased academic performance, low levels of study satisfaction, and eventually drop out. Student support services are facing budget cuts and can only attend to limited numbers of students, usually the ones who present with more severe mental health problems. Moreover, face-to-face contact may not appeal to those students who feel embarrassed by their problems or are afraid of being stigmatised. To address this important problem, an online psychological wellbeing and study skills support system called MePlusMe, has been developed to provide personalised support to its users. In the present study we investigated the feasibility and acceptability of the contents, design, and functionalities of the system. Methods: An offline version of the system was introduced to 13 postgraduate and undergraduate students (mean age = 31.3 years, SD = 10.25 years; 4 males) in a UK HE Institution, who presented with mild or moderate mental health difficulties. The participants evaluated the design of the system, its functionalities, and contents at Baseline and at Weeks 2, 4, and 8. Results: Participants found the system easy to use, professional, and efficient and its contents non-judgemental and informative. Participants stated that engaging with and practicing the techniques targeted at mental health difficulties led to improvements in positive thinking and self-confidence, while the study skills techniques were practical. Suggestions for further improvement included the development of an app and an option for direct engagement with professionals. Conclusions: The findings confirmed the acceptability of the contents, design and functionalities of the system, while providing useful information to inform its further development. Next steps include a feasibility study, which will test and quantify the effects on everyday functioning, mood, mental wellbeing, and academic self-efficacy after using the system, and subsequently a randomized controlled trial, which will evaluate its effectiveness

Fragment-based discovery of a regulatory site in thioredoxin glutathione reductase acting as "doorstop" for NADPH entry

Members of the FAD/NAD-linked reductase family are recognized as crucial targets in drug development for cancers, inflammatory disorders, and infectious diseases. However, individual FAD/NAD reductases are difficult to inhibit in a selective manner with off target inhibition reducing usefulness of identified compounds. Thioredoxin glutathione reductase (TGR), a high molecular weight thioredoxin reductase-like enzyme, has emerged as a promising drug target for the treatment of schistosomiasis, a parasitosis afflicting more than 200 million people. Taking advantage of small molecules selected from a high-throughput screen and using X-ray crystallography, functional assays, and docking studies, we identify a critical secondary site of the enzyme. Compounds binding at this site interfere with well-known and conserved conformational changes associated with NADPH reduction, acting as a doorstop for cofactor entry. They selectivity inhibit TGR from Schistosoma mansoni and are active against parasites in culture. Since many members of the FAD/NAD-linked reductase family have similar catalytic mechanisms the unique mechanism of inhibition identified in this study for TGR broadly opens new routes to selectively inhibit homologous enzymes of central importance in numerous diseases

Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells

The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN∕GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at ∼420nm is achieved under pulsed excitation at room temperature for a peak power density of 400kW/cm2. The lasing emission linewidth is down to 0.033nm

Metallo-dielectric diamond and zinc-blende photonic crystals

It is shown that small inclusions of a low absorbing metal can have a dramatic effect on the photonic band structure. In the case of diamond and zinc-blende photonic crystals, several complete photonic band gaps (CPBG's) can open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike in the purely dielectric case, in the presence of small inclusions of a low absorbing metal the largest CPBG for a moderate dielectric constant (epsilon<=10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most important CPBG, because it is the most stable against disorder. For a diamond and zinc-blende structure of nonoverlapping dielectric and metallo-dielectric spheres, a CPBG begins to decrease with an increasing dielectric contrast roughly at the point where another CPBG starts to open--a kind of gap competition. A CPBG can even shrink to zero when the dielectric contrast increases further. Metal inclusions have the biggest effect for the dielectric constant 2<=epsilon<=12, which is a typical dielectric constant at near infrared and in the visible for many materials, including semiconductors and polymers. It is shown that one can create a sizeable and robust 2nd-3rd CPBG at near infrared and visible wavelengths even for a photonic crystal which is composed of more than 97% low refractive index materials (n<=1.45, i.e., that of silica glass or a polymer). These findings open the door for any semiconductor and polymer material to be used as genuine building blocks for the creation of photonic crystals with a CPBG and significantly increase the possibilities for experimentalists to realize a sizeable and robust CPBG in the near infrared and in the visible. One possibility is a construction method using optical tweezers, which is analyzed here.Comment: 25 pp, 23 figs, RevTex, to appear in Phys Rev B. For more information look at http://www.amolf.nl/research/photonic_materials_theory/moroz/moroz.htm

Targeted Sequencing of Candidate Regions Associated with Sagittal and Metopic Nonsyndromic Craniosynostosis

Craniosynostosis (CS) is a major birth defect in which one or more skull sutures fuse prematurely. We previously performed a genome-wide association study (GWAS) for sagittal nonsyndromic CS (sNCS), identifying associations downstream from BMP2 on 20p12.3 and intronic to BBS9 on 7p14.3; analyses of imputed variants in DLG1 on 3q29 were also genome-wide significant. We followed this work with a GWAS for metopic non-syndromic NCS (mNCS), discovering a significant association intronic to BMP7 on 20q13.31. In the current study, we sequenced the associated regions on 3q29, 7p14.3, and 20p12.3, including two candidate genes (BMP2 and BMPER) near some of these regions in 83 sNCS child-parent trios, and sequenced regions on 7p14.3 and 20q13.2-q13.32 in 80 mNCS child-parent trios. These child-parent trios were selected from the original GWAS co-horts if the probands carried at least one copy of the top associated GWAS variant (rs1884302 C allele for sNCS; rs6127972 T allele for mNCS). Many of the variants sequenced in these targeted regions are strongly predicted to be within binding sites for transcription factors involved in crani-ofacial development or bone morphogenesis. Variants enriched in more than one trio and predicted to be damaging to gene function are prioritized for functional studies

Four-dimensional distribution of the 2010 Eyjafjallajökull volcanic cloud over Europe observed by EARLINET

© Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License.The eruption of the Icelandic volcano Eyjafjallaj ökull in April-May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4-D) distribution of the Eyjafjallajökull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April-26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local planetary boundary layer (PBL). After 19 April 2010, volcanic particles were detected over southern and south-eastern Europe. During the first half of May (5-15 May), material emitted by the Eyjafjallajökull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. The last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4-D distribution of volcanic aerosol layering and optical properties on European scale reported here provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events.Peer reviewe