NUS High School of Mathematics and Science

We experimentally demonstrate at terahertz frequencies that a planar metamaterial exhibits a spectral response resembling electromagnetically induced transparency. The metamaterial unit cell consists of a split ring surrounded by another closed ring where their dimensions are such that their excitable lowest order modes have identical resonance frequencies but very different lifetimes. Terahertz time-domain spectroscopy verifies that the interference of these two resonances results in a narrow transparency window located within a broad opaque region. In contrast to previous studies this enhanced transmission is achieved by independently exciting two resonances in which their coupling to the radiation field, and thus their linewidth, differs strongly. Rigorous numerical simulations prove that the transparency window is associated with a large group index and low losses, making the design potentially useful for slow light applications. This experiment opens an avenue to explore quantum-mechanical phenomena using localized resonances in metallic structures.

We experimentally study the effect of near field coupling on the transmission of light in terahertz metasurfaces. Our results show that tailoring the coupling between the resonators modulates the amplitude of resulting electromagnetically induced transmission, probed under different types of asymmetries in the coupled system. Observed change in the transmission amplitude is attributed to the change in the amount of destructive interference between the resonators in the vicinity of strong near field coupling. We employ a two-particle model to theoretically study the influence of the coupling between bright and quasi-dark modes on the transmission properties of the system and we find an excellent agreement with our observed results. Adding to the enhanced transmission characteristics, our results provide a deeper insight into the metamaterial analogues of atomic electromagnetically induced transparency and offer an approach to engineer slow light devices, broadband filters, and attenuators at terahertz frequencies.

CuCo2O4 and CuO·Co3O4 compounds were prepared by a one-pot simple molten salt method (MSM) at 280 °C to 750 °C. Changes in morphology, crystal structure and electrochemical properties of CuCo2O4 as a function of preparation temperatures were investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer–Emmett–Teller absorption isotherm. XRD patterns of the sample prepared at 280 °C show a crystalline cubic structure with a lattice parameter value of a = 8.131 Å and a surface area value of 9.8 m2 g−1. The sample prepared at temperatures >510 °C shows the presence of CuO·Co3O4 phases. Energy storage properties are evaluated using cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies show a main anodic peak at ∼2.1 V and cathodic peak at ∼1.2 V. At a current rate of 60 mA g−1 and in the voltage range of 0.005–3.0 V vs. Li, CuCo2O4 composite prepared at 510 °C shows a high and stable capacity of ∼680 (quenched) and 740 (slow cooling) mAh g−1 at the end of the 40th cycle.

Exfoliated graphene oxide (EG)/MoO2 composites are synthesized by a simple solid-state graphenothermal reduction method. Graphene oxide (GO) is used as a reducing agent to reduce MoO3 and as a source for EG. The formation of different submicron sized morphologies such as spheres, rods, flowers, etc., of monoclinic MoO2 on EG surfaces is confirmed by complementary characterization techniques. As-synthesized EG/MoO2 composite with a higher weight percentage of EG performed excellently as an anode material in lithium-ion batteries. The galvanostatic cycling studies aided with postcycling cyclic voltammetry and galvanostatic intermittent titrations followed by ex situ structural studies clearly indicate that Li intercalation into MoO2 is transformed into conversion upon aging at low current densities while intercalation mechanism is preferably taking place at higher current rates. The intercalation mechanism is found to be promising for steady-state capacity throughout the cycling because of excess graphene and higher current density even in the operating voltage window of 0.005-3.0 V in which MoO2 undergoes conversion below 0.8 V.

Fenretinide is a synthetic retinoid that is being tested in clinical trials for the treatment of breast cancer and insulin resistance, but its mechanism of action has been elusive. Recent in vitro data indicate that fenretinide inhibits dihydroceramide desaturase, an enzyme involved in the biosynthesis of lipotoxic ceramides that antagonize insulin action. Because of this finding, we assessed whether fenretinide could improve insulin sensitivity and glucose homeostasis in vitro and in vivo by controlling ceramide production. The effect of fenretinide on insulin action and the cellular lipidome was assessed in a number of lipid-challenged models including cultured myotubes and isolated muscles strips incubated with exogenous fatty acids and mice fed a high-fat diet. Insulin action was evaluated in the various models by measuring glucose uptake or disposal and the activation of Akt/PKB, a serine/threonine kinase that is obligate for insulin-stimulated anabolism. The effects of fenretinide on cellular lipid levels were assessed by LC-MS/MS. Fenretinide negated lipid-induced insulin resistance in each of the model systems assayed. Simultaneously, the drug depleted cells of ceramide, while promoting the accumulation of the precursor dihydroceramide, a substrate for the reaction catalyzed by Des1. These data suggest that fenretinide improves insulin sensitivity, at least in part, by inhibiting Des1 and suggest that therapeutics targeting this enzyme may be a viable therapeutic means for normalizing glucose homeostasis in the overweight and diabetic.

10.1149/2.089112jes

Spinel MCo2O4 (M = Mg, Mn) materials were synthesized using a template free molten salt method with various precursor salts. Powder X-ray diffraction, Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy, and transmission electron microscopy were carried out to characterize the phase, structure, and morphology of the compounds. Electrochemical cycling was carried out between voltages 0.005 and 3.0 V was carried out on button cells. At the end of cycling using 60 mA g–1, MgCo2O4 showed reversible capacity of 816 (±5) mAh g–1 after 50 cycles and MnCo2O4 showed a capacity fading of only 4% after 45 cycles retaining a capacity of 863 (±5) mAh g–1. In addition, cyclic voltammetry and electrochemical impedance spectroscopy were carried out on select cycles to study the electrode kinetics.

We report the synthesis of CuO material by molten salt method at a temperature range, 280 to 950 °C for 3 h in air. This report includes studies on the effect of morphology, crystal structure and electrochemical properties of CuO prepared at different temperatures. Obtained CuO was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area methods. Samples prepared at ≥410 °C showed a single-phase material with a lattice parameter value of a = 4.69 Å, b = 3.43 Å, c = 5.13 Å and surface area values are in the range 1.0-17.0 m(2) g(-1). Electrochemical properties were evaluated via cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies showed a minor difference in the peak potentials depending on preparation temperature and all compounds exhibit a main anodic peak at ~2.45 V and cathodic peaks at ~0.85 V and ~1.25 V vs Li. CuO prepared at 750 °C showed high and stable capacity of ~620 mA h g(-1) at the end of 40th cycle.

Many nucleic acid aptamers that bind to target molecules have been reported as antibody alternatives. However, while the affinities of aptamers vary widely, little is known about the relationship between the affinities and their applicabilities for practical use. Here, we developed molecular affinity rulers: a series of DNA aptamers with different affinities that bind to the same area of target molecules, to measure the aptamer and its device applicabilities. For the ruler preparation, we used high-affinity DNA aptamers containing a hydrophobic unnatural base (Ds) as the fifth base. By replacing Ds bases with A bases in Ds-DNA aptamers targeting VEGF165 and interferon-γ, we prepared two sets of DNA aptamers with dissociation constants (KD) ranging from 10-12 to 10-8 M. Using these molecular affinity rulers, we evaluated the sensitivity of DNA aptamers in ELISA (enzyme-linked immunosorbent assay), which showed the clear relationship between aptamer affinities and their detection sensitivities. In sandwich-type ELISA using combinations of aptamers and antibodies, aptamers with KD values lower than ∼10-9 M were required for sufficient sensitivities (limit of detection (LOD) < 10 pM) and signal intensities, but optimizations improved the lower-affinity aptamers' applicabilities. These aptamer affinity rulers could be useful for evaluating and improving aptamer applicabilities.

10.1149/2.077206jes

We prepared solid solutions based on Ni, Zn, and Fe oxides to be used as nanomaterials for anodes of Li-ion batteries. The materials were synthesized using molten salt method with KCl as the molten salt. The prepared nanomaterials (Ni1–xZnx)Fe2O4 (x = 0, 0.25, 0.5, 0.75, 1) were subsequently characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), the Brunauer–Emmett–Teller surface and density methods. Cyclic voltammetry (CV) and galvanostatic cycling tests were then conducted to understand the lithium storage performance of the electrodes. Electrochemical impedance spectroscopy (EIS) was also performed to analyze the kinetics of our electrodes and other characteristics of the battery cell. The electrochemical properties of prepared compounds showed reversible capacities (mAh/g) of 706, 819, 603, 781, 637 for x = 0, 0.25, 0.5, 0.75, and 1 at the end of the 50th cycle.

The potential of genetic alphabet expansion technologies using artificial extra base pairs (unnatural base pairs) has been rapidly expanding and increasing. We present that the hydrophobic unnatural base, 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds), which acts as a fifth letter in a DNA library, provides a series of high-affinity DNA aptamers with versatile binding specificities and activities to cancer cells. These Ds-containing DNA aptamers were generated by a method called cell-ExSELEX to target three breast cancer cell lines: MCF7, MDA-MB-231, and T-47D. Aptamer 14A-MCF7, which targets MCF7 cells, specifically binds to MCF7 cells, but not other cancer cell lines. Aptamer 07-MB231, which targets MDA-MB-231 cells, binds to a series of metastatic bone and lung cancer cell lines. Aptamer 05-MB231 targets MDA-MB-231 cells, but it also binds to all of the cancer and leukemia cell lines that we examined. None of these aptamers bind to normal cell lines, such as MCF10A and HUVEC. In addition, aptamers 14A-MCF7 and 05-MB231 are internalized within the cancer cells, and aptamer 05-MB231 possesses anti-proliferative properties against most cancer cell lines that we examined. These aptamers and the generation method are broadly applicable to cancer cell imaging, biomarker discovery, cancer cell profiling, anti-cancer therapies, and drug delivery systems. The potential of genetic alphabet expansion technologies using artificial extra base pairs (unnatural base pairs) has been rapidly expanding and increasing. We present that the hydrophobic unnatural base, 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds), which acts as a fifth letter in a DNA library, provides a series of high-affinity DNA aptamers with versatile binding specificities and activities to cancer cells. These Ds-containing DNA aptamers were generated by a method called cell-ExSELEX to target three breast cancer cell lines: MCF7, MDA-MB-231, and T-47D. Aptamer 14A-MCF7, which targets MCF7 cells, specifically binds to MCF7 cells, but not other cancer cell lines. Aptamer 07-MB231, which targets MDA-MB-231 cells, binds to a series of metastatic bone and lung cancer cell lines. Aptamer 05-MB231 targets MDA-MB-231 cells, but it also binds to all of the cancer and leukemia cell lines that we examined. None of these aptamers bind to normal cell lines, such as MCF10A and HUVEC. In addition, aptamers 14A-MCF7 and 05-MB231 are internalized within the cancer cells, and aptamer 05-MB231 possesses anti-proliferative properties against most cancer cell lines that we examined. These aptamers and the generation method are broadly applicable to cancer cell imaging, biomarker discovery, cancer cell profiling, anti-cancer therapies, and drug delivery systems.

In this paper, we draw on a study conducted in Grade 11 classrooms to explore how the learners’ home languages can be used for teaching and learning mathematics in multilingual classrooms in South Africa. This report is part of a wider study that is still in progress. Based on an analysis of data collected through lesson observations in a Grade 11 class and learner interviews we argue for the deliberate, proactive and strategic use of the learners’ home languages as a transparent resource in the teaching and learning of mathematics in multilingual classrooms. Such use of the languages will ensure that learners gain access to mathematical knowledge without losing access to English, which many parents, teachers and learners presently see as a necessary condition for gaining access to social goods such as higher education and employment.

The two Orlando, Fla., high schools described in this article are working toward providing success for all stu dents by implementing restructuring plans generated by their own school communities.

A new TiO₂-coated stirred glass reactor was designed, comprising a film of fluorine-doped tin oxide (FTO) coated on a transparent glass anode.

DNA assembly forms the cornerstone of modern synthetic biology. Despite the numerous available methods, scarless multi-fragment assembly of large plasmids remains challenging. Furthermore, the upcoming wave in molecular biological automation demands a rethinking of how we perform DNA assembly. To streamline automation workflow and minimize operator intervention, a non-enzymatic assembly method is highly desirable. Here, we report the optimization and operationalization of a process called Twin-Primer Assembly (TPA), which is a method to assemble polymerase chain reaction-amplified fragments into a plasmid without the use of enzymes. TPA is capable of assembling a 7 kb plasmid from 10 fragments at ∼80% fidelity and a 31 kb plasmid from five fragments at ∼50% fidelity. TPA cloning is scarless and sequence independent. Even without the use of enzymes, the performance of TPA is on par with some of the best in vitro assembly methods currently available. TPA should be an invaluable addition to a synthetic biologist's toolbox.

We present scanning focused laser beam as a multipurpose tool to engineer the physical and chemical properties of WS2 microflakes. For monolayers, the laser modification integrates oxygen into the WS2 microflake, resulting in ∼9 times enhancement in the intensity of the fluorescence emission. This modification does not cause any morphology change, allowing “micro-encryption” of information that is only observable as fluorescence under excitation. The same focused laser also facilitates on demand thinning down of WS2 multilayers into monolayers, turning them into fluorescence active components. With a scanning focused laser beam, micropatterns are readily created on WS2 multilayers through selective thinning of specific regions on the flake.

PURPOSE:: We aim to determine whether hyperlactatemia, which suggests multi-organ dysfunction and impaired organic substrate metabolism, may predict intolerance to regional citrate anticoagulation (RCA) during continuous venovenous hemofiltration (CVVH). METHODS:: We performed a single-center, retrospective observational study in critically ill patients with acute kidney injury or end-stage renal disease and evaluated the association of peak serum lactate levels with citrate intolerance (CI) during the initial 72 hours of RCA-CVVH, defined by serum total-to-ionized calcium >2.5 plus systemic hypocalcemia. RESULTS:: Eighty-eight patients were studied (aged 59 ± 14 years, 66% males, Acute Physiology and Chronic Health Evaluation II: 31 ± 8). Citrate was dosed at median 2.1 mmol/L of blood flow, with citrate load of 30 mmol/h, and CVVH effluent of 43 mL/kg/h. Twenty patients developed CI. Comparing patients with CI versus none, peak lactate levels were 8 (5-11) versus 3 (2-6) mmol/L, calcium replacement was 13 (10-17) versus 11 (8-12) mmol/h, and standard base excess was -4 (-12 to 1) versus 2(-4 to 7) mmol/L, respectively ( P < .05). Citrate intolerance developed in 38%, 44%, and 55%, in patients with peak lactate >4, >6, >7 mmol/L, respectively, versus 7% in those with peak lactate ≤4 mmol/L ( P ≤ .001), despite comparable citrate load and effluent rates across all categories. On multivariate analysis, hyperlactatemia and hyperbilirubinemia predicted CI ( P ≤ .01), which was associated with increasing calcium infusion requirement. Higher peak lactate from >4 to >7 mmol/L predicted CI with graded increase in odds ratio and specificity from 59% to 87%, but the corresponding negative predictive value from 93% to 87%. Area under nonparametric receiver operating characteristic curve for peak lactate and CI was 0.78. CONCLUSION:: Hyperlactatemia predicts CI during RCA-CVVH with reasonable discriminatory performance in critically ill patients. Serum lactate surveillance may help preempt issues with citrate toxicity.

OBJECTIVES: Multiresistant Gram-negative pathogens pose major healthcare concerns with a limited therapeutic armamentarium. Aminoglycosides (AG) are under-utilized due to nephrotoxicity. We aimed to evaluate AG-associated acute kidney injury (AG-AKI) in elderly inpatients, with and without shock. METHODS: We examined the incidence and predictors of AG-AKI by KDIGO criteria and extended renal dysfunction (ERD) in patients aged >60 years. ERD represented a composite of hospital mortality or absence of renal recovery over 6 months following AG-AKI. RESULTS: Two hundred and seventy-eight patients (aged 74 ± 8 years) were studied; 43% and 19% received >7 and >10 days of AG therapy, respectively, and 70% gentamicin (versus amikacin). Thirteen per cent had shock and 17% developed AG-AKI. Comparing all patients with shock versus no shock, AG-AKI developed in 33% versus 14%, respectively (P = 0.005); correspondingly among 47 patients with AG-AKI, more with shock had stage 2/3 AKI (92% versus 43%) and dialysis (50% versus 9%) (P < 0.01), but more had other strong AKI confounders than AG therapy alone (83% versus 40%, P = 0.02). Multivariate analyses identified mechanical ventilation, frusemide administration and AG therapy >10 days as predictors of AG-AKI (P < 0.05), whereas shock, pneumonia and frusemide administration predicted more severe stage 2/3 AG-AKI (P < 0.05). Hospital mortality was 30% versus 7% with AG-AKI versus none (P < 0.001). Twenty-three of 211 (11%) patients with extended analysis had ERD, with 47% experiencing renal recovery following AG-AKI. Mechanical ventilation and contrast administration during index hospitalization predicted ERD (P < 0.05). CONCLUSIONS: AG-AKI is common in the elderly, with a significant risk of ERD, but the cause and severity are greatly influenced by critical illness and shock, more so than AG therapy alone.

We attempted to prepare SnO2 based oxide materials by molten salt method (MSM) using KCl at 850 and 1050 °C and 0.5 M KCl/0.5 M NaCl at 650 °C for 3 h in air. The compounds were characterized by Rietveld refined X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area methods. XRD studies show tetragonal SnO2 type structure. Compounds exhibited surface areas ranging from 0.78 to 5.68 m2 g–1. The electrochemical (anodic) behavior of samples prepared at 850 and 650 °C were examined by galvanostatic cycling (GC) and cyclic voltammetry (CV) vs Li-metal in the voltage range 0.005–1.0 V or 0.005–3.0 V vs Li. All compounds display the main cathodic peak at ∼0.25 V and anodic peak at ∼0.5 V based on the CV studies, which are characteristic cathodic and anodic peaks of SnO2. Anodic properties showed reversible capacity values in the range 631–679 mAhg–1 in the voltage range, 0.005–1.0 V vs Li. Tin oxides made from Co-sulfate and SnCl2 generally displayed a high storage capacity with good capacity retention. When we cycled to higher cutoff voltage (0.005–3.0 V), capacity fading was noted in all compounds due to the huge volume variation conversion reaction of respective Sn-oxides.