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Phase inconsistency as a major source of error in NGFS forecast
No full textSouth Asian monsoon exhibits multiscale spatiotemporal variability. Analyzing the nature and behavior of numerical weather forecast error associated with these space-time heterogeneities will eventually help in improving the models. We investigate the spatiotemporal error characteristics of the National Centre for Medium-Range Weather Forecasting (NCMRWF) Global Forecast System (NGFS) model over South Asian land and ocean separately. Although error grows with lead-time, it saturates within 3�5 days of forecast initiation. The saturated error is only about 15�25 higher than that of day-1, indicating that most of the error accumulates within first 24-h of forecast. Increase in error over oceanic regions is due to an increase in the area with high error at all precipitation ranges with large day-to-day variability. However, over land error growth is primarily confined at locations of high mean precipitation. Decomposition of error arising due to intensity and phase variations reveals that about 90 of it arises from the model�s inability to capture phase of precipitation at various timescales. We show that NGFS cannot capture synoptic scale variations (< 10 day) after day-2. Both the high-frequency (10�20 day) and low-frequency (30�60 day) intraseasonal variations are reasonably predicted up to day-3. At diurnal timescale, NGFS forecasts show a peak in precipitation about 3�6 h prior to that observed, both over land and ocean. Surprisingly, this error does not change with lead-time. Lastly, we show that major error characteristics do not depend on the seasonal mean monsoon rainfall
Entanglement of near-surface optical turbulence to atmospheric boundary layer dynamics and particulate concentration: Implications for optical wireless communication systems
No full textLocalized reduction in optical turbulence due to enhanced atmospheric heating caused by the solar absorption of aerosol black carbon (BC) is reported. Immediate response of atmospheric turbulence to BC-induced atmospheric warming strongly depends on the available solar radiation (time of the day), BC concentration, and atmospheric boundary layer dynamics. Besides the significant climate implications of a reduction in turbulence kinetic energy, a large reduction in the refractive index structure parameter (C2 n) resulting from BC-induced warming would affect the atmospheric propagation of laser beams. Interestingly, aerosols contribute significantly (up to 25) to the signal deterioration in optical wireless communication systems during convectively stable atmospheric conditions when higher signal-to-noise ratios are expected otherwise due to the reduced thermal convection. Competing effects of the fractional contributions of aerosol extinction and scintillations on beam attenuation are reported; daytime being largely dominated by scintillation effects while the nighttime being dependent on the ambient aerosol concentration as well. We put forward the entanglement of optical turbulence to aerosol concentration, atmospheric boundary layer dynamics, and surface-reaching solar radiation, and discuss the possible implications for optical propagation
Shear moduli of metal specimens using resonant column tests
No full textThe shear moduli of cylindrical metal specimens were determined by performing resonant column tests in a torsional mode of vibration. The tests were performed on four different metals, namely (i) aluminum, (ii) brass, (iii) copper, and (iv) mild steel. Keeping the length (L) of the specimens the same, different diameters (d) were chosen to vary the torsional stiffness and, thereby, the resonant frequency. Additional circular plates were attached to the top of the drive mechanism to have different resonant frequencies with the same torsional stiffness (K T ). The shear moduli (G) were established by two different methods, namely (i) from the evaluation of K T and (ii) by first determining the mass moment of inertia (J d ) of the drive mechanism and then finding G from the measured circular resonant frequency (� n ). Both the methods provide exactly the same answer(s). For aluminum and brass, the measurement of the shear modulus was found to be much more accurate; the maximum variation of the shear modulus with diameter (8-12 mm/15 mm) for the same driving input voltage (torque) was around 3.3 for aluminum and 1.2 for brass. On the other hand, in the case of mild steel and copper, the variation of shear modulus was around 9.2 and 7.2 , respectively. The measured values of the shear moduli were found to compare well with the data reported from literature for the different chosen metals. Copyright © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-295
A simple and cost-efficient technique to generate hyperpolarized long-lived 15N-15N nuclear spin order in a diazine by signal amplification by reversible exchange
No full textSignal Amplification by Reversible Exchange (SABRE) is an inexpensive and simple hyperpolarization technique that is capable of boosting nuclear magnetic resonance sensitivity by several orders of magnitude. It utilizes the reversible binding of para-hydrogen, as hydride ligands, and a substrate of interest to a metal catalyst to allow for polarization transfer from para-hydrogen into substrate nuclear spins. While the resulting nuclear spin populations can be dramatically larger than those normally created, their lifetime sets a strict upper limit on the experimental timeframe. Consequently, short nuclear spin lifetimes are a challenge for hyperpolarized metabolic imaging. In this report, we demonstrate how both hyperpolarization and long nuclear spin lifetime can be simultaneously achieved in nitrogen-15 containing derivatives of pyridazine and phthalazine by SABRE. These substrates were chosen to reflect two distinct classes of 15N2-coupled species that differ according to their chemical symmetry and thereby achieve different nuclear spin lifetimes. The pyridazine derivative proves to exhibit a signal lifetime of �2.5 min and can be produced with a signal enhancement of �2700. In contrast, while the phthalazine derivative yields a superior 15 000-fold 15N signal enhancement at 11.7 T, it has a much shorter signal lifetime
On the Growth of the Bergman Metric Near a Point of Infinite Type
No full textWe derive optimal estimates for the Bergman kernel and the Bergman metric for certain model domains in C2 near boundary points that are of infinite type. Being unbounded models, these domains obey certain geometric constraints�some of them necessary for a non-trivial Bergman space. However, these are mild constraints: unlike most earlier works on this subject, we are able to make estimates for non-convex pseudoconvex models as well. In fact, the domains we can analyse range from being mildly infinite-type to very flat at infinite-type boundary points
Crystallographic inversion-mediated superparamagnetic relaxation in Zn-ferrite nanocrystals
No full textCrystallographic inversion induced shift of resonance frequency in zinc ferrite nanoparticle (ZF-NP) samples is studied here. ZF-NP samples were synthesized by a solution-based, low-temperature (<200 °C), microwave-assisted solvothermal (MAS) process. Owing to the far-from-equilibrium processing condition, the MAS process produces a very high degree of crystallographic inversion, δ=0.61, in the as-synthesized nanocrystallites. A rapid thermal annealing (RTA) technique was adopted to tune-down crystallographic inversion without altering the crystallite sizes in annealed samples. The crystal structures, particle shapes, and compositions of the nanocrystalline samples were characterized by XRD, SEM and Raman spectroscopy. The samples are phase-pure, with particle size in the range 8-16 nm and their compositions are stoichiometrically accurate. The resonance phenomena in 1 to 10 GHz frequency range was measured by analyzing the impedance mismatch of a microstrip line with the magnetic material loaded on to it. The RTA protocol enables tuning of the resonance phenomena in the ZF-NC samples above 6 GHz with tunable range of �500 MH
Importance and vulnerability of the world�s water towers
No full textMountains are the water towers of the world, supplying a substantial part of both natural and anthropogenic water demands1,2. They are highly sensitive and prone to climate change3,4, yet their importance and vulnerability have not been quantified at the global scale. Here we present a global water tower index (WTI), which ranks all water towers in terms of their water-supplying role and the downstream dependence of ecosystems and society. For each water tower, we assess its vulnerability related to water stress, governance, hydropolitical tension and future climatic and socio-economic changes. We conclude that the most important (highest WTI) water towers are also among the most vulnerable, and that climatic and socio-economic changes will affect them profoundly. This could negatively impact 1.9 billion people living in (0.3 billion) or directly downstream of (1.6 billion) mountainous areas. Immediate action is required to safeguard the future of the worlds most important and vulnerable water towers
Active modulation of surfactant-driven flow instabilities by swarming bacteria
No full textModels based on surfactant-driven instabilities have been employed to describe pattern formation by swarming bacteria. However, by definition, such models cannot account for the effect of bacterial sensing and decision making. Here we present a more complete model for bacterial pattern formation which accounts for these effects by coupling active bacterial motility to the passive fluid dynamics. We experimentally identify behaviors which cannot be captured by previous models based on passive population dispersal and show that a more accurate description is provided by our model. It is seen that the coupling of bacterial motility to the fluid dynamics significantly alters the phase space of surfactant-driven pattern formation. We also show that our formalism is applicable across bacterial species
Pressure-induced electronic and isostructural phase transitions in PdPS: Raman, x-ray, and first-principles study
No full textApplication of pressure is known to be an effective tool for tuning structural and electronic properties of transition metal dichalcogenides. In this work we present evolution of PdPS with pressure using Raman spectroscopy and synchrotron x-ray diffraction up to 26 GPa, complemented with first-principles theoretical analysis of PdPS under pressure up to 36 GPa. Raman spectra reveal changes in the pressure derivatives of Raman frequencies at P�2, 11, and 21 GPa, suggesting three isostructural electronic phase transitions in PdPS. The pressure-dependent x-ray diffraction shows a sudden rise in the bulk modulus from 90±3 to 123±7 GPa occurring at P�11 GPa. Using first-principles density functional theory calculations, we demonstrate that the low-pressure phase transitions are associated with changes in direct band gap at � point while the high-pressure (at P=21 GPa) transition is associated with semiconductor to semimetal transition. From analysis of PdPS at higher pressures, we predict a structural phase transition in PdPS at P�32 GPa from orthorhombic to monoclinic structure
Predicting interfacial hot-spot residues that stabilize protein-protein interfaces in oligomeric membrane-toxin pores through hydrogen bonds and salt bridges
No full textPore forming toxins (PFTs) are proteins which form unregulated oligomeric pores on target plasma membranes to cause ion leakage and cell death and represent the largest class of bacterial virulence factors. With increasing antibiotic-resistant bacterial strains, alternate therapies are being developed to target toxin pore formation rather than the bacteria themselves. One strategy is to undermine the stability of these multimeric pores, whose subunits are held together by complex amino acid interaction networks, by identifying key residues in these networks which could be plausible drug or mutagenesis targets. However, this requires a quantitative assessment of per residue contributions towards pore stability, which cannot be reliably gleaned from static crystal/cryo-EM pore structures. In this study, we overcome this limitation by developing a computational screening algorithm that employs fully atomistic molecular dynamics simulations coupled with energy-based screening that can predict �hot-spot� residues which engage in persistent and stabilizing hydrogen bonds or salt bridges across protein-protein interfaces. Application of this algorithm to prototypical α-PFT (cytolysin A) and β-PFT (α-hemolysin) membrane-inserted pores yielded a small predicted set of highly interacting residues, blocking of which could destabilize pore complexes. Previous mutagenesis studies validate some of our in silico predictions. The algorithm could be applied to all pores with known structures to generate a database of destabilizing mutations, which could then serve as a basis for experimental validation and rational structure-based inhibitor design