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Inferring critical thresholds of ecosystem transitions from spatial data
No full textEcosystems can undergo abrupt transitions between alternative stable states when the driver crosses a critical threshold. Dynamical systems theory shows that when ecosystems approach the point of loss of stability associated with these transitions, they take a long time to recover from perturbations, a phenomenon known as critical slowing down. This generic feature of dynamical systems can offer early warning signals of abrupt transitions. However, these signals are qualitative and cannot quantify the thresholds of drivers at which transition may occur. Here, we propose a method to estimate critical thresholds from spatial data. We show that two spatial metrics, spatial variance and autocorrelation of ecosystem state variable, computed along driver gradients can be used to estimate critical thresholds. First, we investigate cellular-automaton models of ecosystem dynamics that show a transition from a high-density state to a bare state. Our models show that critical thresholds can be estimated as the ecosystem state and the driver values at which spatial variance and spatial autocorrelation of the ecosystem state are maximum. Next, to demonstrate the application of the method, we choose remotely sensed vegetation data (Enhanced Vegetation Index, EVI) from regions in central Africa and northeast Australia that exhibit alternative states in woody cover. We draw transects (8 x 90 km) that span alternative stable states along rainfall gradients. Our analyses of spatial variance and autocorrelation of EVI along transects yield estimates of critical thresholds. These estimates match reasonably well with those obtained by an independent method that uses large-scale (250 x 200 km) spatial data sets. Given the generality of the principles that underlie our method, our method can be applied to a variety of ecosystems that exhibit alternative stable states
Integration of multi-layered materials with wide bandgap semiconductors for multi-spectral photodetectors: case for MoS2/GaN and beta-In2Se3/GaN
No full textWe report on the demonstration of UV/visible and UV/near-IR photodetectors of high spectral responsivity (SR) in a non-conventional heterojunction, realized by combining multi-layered materials with wide band gap Gallium Nitride (GaN). Multi-layer MoS2 and beta-In2Se3 flakes were exfoliated separately on epitaxial GaN-on-sapphire, followed by fabrication of photodetectors in a lateral inter-digitated metal semiconductor metal geometry with Ti/Au contacts. Devices exhibited distinct steps in SR graph at 365 nm with responsivity value of 127 AW(-1) and at similar to 685 nm with responsivity value of 33 AW(-1) for MoS2/GaN heterostructure. Whereas, similar steps exhibited at 365 nm with responsivity value of 1.6 AW(-1) and at similar to 850 nm with responsivity value of 0.03 AW-1 in case of beta-In2Se3/GaN heterostructure. The wavelength dependent I-V characteristics showed photo-to-dark current ratio of similar to 30 at 685 nm in case of MoS2/GaN heterostructure and ratio of similar to 2 at 850 nm for beta-In2Se3/GaN heterostructure. The reasons which limit the performance of the devices were also investigated using transient analysis and power dependent responsivity analysis. In summary, current work paves the way for futuristic layered-materials/3D heterostructure devices
Use of a weather forecast model to identify suitable sites for new wind power plants in Karnataka
No full textThe wind speed forecast by a weather forecast model (with a resolution of 3 km) has been used to identify regions with high wind speed in Karnataka. The correlation between daily wind speed predicted by the model and the measured wind speed at three stations in Karnataka has been shown to be high. Based on this model, new locations have been suggested for the installation of new wind power plants in Karnataka
Equivalent Circuit Analysis of a Rectangular Double-Reentrant Cavity With Circular Cylindrical Ferrule for Klystrons
No full textEquivalent circuit analysis of a rectangular double-reentrant cavity of klystron with circular cylindrical ferrule operating in the fundamental TM110 mode was developed for obtaining the lumped parameters such as capacitance and inductance by considering the cavity as a parallel resonant circuit. Resonant frequency and characteristic shunt impedance of the cavity were then obtained using these lumped parameters. Analysis was validated against 3-D electromagnetic simulations using CST Studio and measurements
Structure-Function Studies of the Bacillus subtilis Ric Proteins Identify the Fe-S Cluster-Ligating Residues and Their Roles in Development and RNA Processing
No full textIn Bacillus subtilis, the RicA (YmcA), RicF (YlbF), and RicT (YaaT) proteins accelerate the phosphorylation of the transcription factor Spo0A, contributing to genetic competence, sporulation, and biofilm formation, and are also essential for the correct maturation of several protein-encoding and riboswitch RNAs. These proteins form a stable complex (RicAFT) that carries two 4Fe-4S](+2) clusters. We show here that the complex is a 1:1:1 heterotrimer, and we present the X-ray crystal structures of a RicAF heterotetramer and of a RicA dimer. We also demonstrate that one of the Fe-S clusters (cluster 1) is ligated by cysteine residues donated exclusively by RicT and can be retained when the RicT monomer is purified by itself. Cluster 2 is ligated by C167 from RicT, by C134 and C146 located near the C terminus of RicF, and by C141 at the C terminus of RicA. These findings imply the following novel arrangement: adjacent RicT residues C166 and 167 ligate clusters 1 and 2, respectively, while cluster 2 is ligated by cysteine residues from RicT, RicA, and RicF. Thus, the two clusters must lie close to one another and at the interface of the RicAFT protomers. We also show that the cluster-ligating cysteine residues, and therefore most likely both Fe-S clusters, are essential for cggR-gapA mRNA maturation, for the regulation of ricF transcript stability, and for several Ric-associated developmental phenotypes, including competence for transformation, biofilm formation, and sporulation. Finally, we present evidence that RicAFT, RicAF, and RicA and the RicT monomer may play distinct regulatory roles in vivo. IMPORTANCE The RicA, RicF, and RicT proteins are widely conserved among the firmicute bacteria and play multiple roles in Bacillus subtilis. Among the phenotypes associated with the inactivation of these proteins are the inability to be genetically transformed or to form biofilms, a decrease in sporulation frequency, and changes in the stability and maturation of multiple RNA species. Despite their importance, the molecular mechanisms of Ric protein activities have not been elucidated and the roles of the two iron-sulfur clusters on the complex of the three proteins are not understood. To unravel the mechanisms of Ric action, molecular characterization of the complex and of its constituent proteins is essential. This report represents a major step toward understanding the structures of the Ric proteins, the arrangement and roles of the Fe-S clusters, and the phenotypes associated with Ric mutations
Elastic properties of few unit cell thick superconducting crystals of Bi2Sr2CaCu2O8+delta
No full textWe present systematic measurements of the mechanical properties of few unit cell (UC) thick exfoliated crystals of a high-T-c cuprate superconductor Bi2Sr2CaCu2O8+delta. We determine the elastic properties of these crystals by deformation using an atomic force microscope at room temperature. With the spatial measurements of local compliance and their detailed modeling, we independently determine the Young's modulus of rigidity and the prestress. The Young's modulus of rigidity is found to be in the range of 22 GPa-30 GPa for flakes with a thickness from similar to 5 UC to 18 UC. The prestress spreads over the range of 5 MPa-46 MPa, indicating a run-to-run variation during the exfoliation process. The determination of Young's modulus of rigidity for thin flakes is further verified from the recently reported buckling technique
The cancer-associated, gain-of-function TP53 variant P152Lp53 activates multiple signaling pathways implicated in tumorigenesis
No full textTP53 is the most frequently mutated tumor suppressor gene in many cancers, yet biochemical characterization of several of its reported mutations with probable biological significance have not been accomplished enough. Specifically, missense mutations in TP53 can contribute to tumorigenesis through gain-of-function of biochemical and biological properties that stimulate tumor growth. Here, we identified a relatively rare mutation leading to a proline to leucine substitution (P152L) in TP53 at the very end of its DNA-binding domain (DBD) in a sample from an Indian oral cancer patient. Although the P152Lp53 DBD alone bound to DNA, the full-length protein completely lacked binding ability at its cognate DNA motifs. Interestingly, P152Lp53 could efficiently tetramerize, and the mutation had only a limited impact on the structure and stability of full-length p53. Significantly, when we expressed this variant in a TP53-null cell line, it induced cell motility, proliferation, and invasion compared with a vector-only control. Also, enhanced tumorigenic potential was observed when P152Lp53-expressing cells were xenografted into nude mice. Investigating the effects of P152Lp53 expression on cellular pathways, we found that it is associated with up-regulation of several pathways, including cell-cell and cell-extracellular matrix signaling, epidermal growth factor receptor signaling, and Rho-GTPase signaling, commonly active in tumorigenesis and metastasis. Taken together, our findings provide a detailed account of the biochemical and cellular alterations associated with the cancer-associated P152Lp53 variant and establish it as a gain-of-function TP53 variant
Establishing empirical correlation between sediment thickness and resonant frequency using HVSR for the Indo-Gangetic Plain
No full textIn this study, microtremor survey was carried out at 31 locations of Indo-Gangetic Plains (IGP) using a pair of portable three-component short-period seismometers (Guralp CMG-6T-1) and Kelunji Echo Pro digital data acquisition system. The acquired raw data was processed to obtain the average H/V ratio of the ambient vibration spectrum. The frequency corresponding to the first peak of the average H/V spectrum was taken as resonant frequency of that particular site. A comparison was made between the resonant frequencies obtained from peak of the H/V spectrum with those obtained using the source-receiver function from previously published work. The results were in good agreement with each other. An empirical equation has been established for the IGP by relating resonance frequency with sediment thickness, using available data from nearby boreholes drilled up to bedrock. The empirical equation was compared with other equations available for deep soil sites, i.e. sites with soil thickness more than 750 m. Further, a combined equation was developed for the digitized data taken from previously published works of deep soil sites. Finally, it has been found that the region-specific equation gives better estimate of sediment thickness than the other empirical equations; but in absence of such a region-specific equation, the proposed combined equation can be used for a quick preliminary assessment of sediment thickness of a deep soil region
Multifunctional magnetic-polymeric nanoparticles based ferrofluids for multi-modal in vitro cancer treatment using thermotherapy and chemotherapy
No full textIn this work, we have developed novel multifunctional magnetic-polymeric nanoparticles (MMPNs) based ferrofluids by encapsulating oleylamine (OM)-coated hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) inside the poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) individually, and along with two drugs such as curcumin (Cur, a chemotherapeutic drug (CHD)), and/or verapamil (Ver, a calcium channel blocker (CCB)). Herein, several parameters such as weighed amount (wt%) of PLGA polymer (i.e., Resomer), stabilizer (i.e., polyvinyl alcohol (PVA)), organic solvents, amount of the SPIONs (in liquid suspension and powder forms), and amount of the drugs (i.e., Cur or/and Ver) are varied during the encapsulation process to optimize the formulation of PLGA NPs. The resulting polymeric NPs including empty PLGA NPs (i.e., without SPIONs/drugs), and MMPNs such as SPIONs-loaded PLGA NPs, Cur-SPIONs-loaded PLGA NPs, Ver-SPIONs-loaded PLGA NPs, and Cur-Ver-SPIONs-loaded PLGA NPs have displayed (i) hydrodynamic diameters and zeta potentials in the range of 280.8-2873 nm, and -21 to - 26 mV, respectively, and (ii) better encapsulation efficiency for the SPIONs/Cur/Ver. In addition, the MMPNs have exhibited (i) magnetization values in the range of 7.6-9.5 emu/g with superparamagnetic behaviour, (ii) concentration based time-dependent temperature raise up-to 42 degrees C (minimum therapeutic temperature in magnetic fluid hyperthermia (MFH)/thermotherapy) with heating efficacies i.e., specific absorption rate (SAR) and intrinsic loss power (ILP) values ranging from 7 to 36 W/gFe and 0.1-0.4 nHm(2)/kg, respectively and (iii) better cytocompatibility. Finally, the SPIONs and dual-drugs (Cur &Ver) co-loaded PLGA NPs have shown enhanced therapeutic efficacy in HepG2 cancer cells via combined therapies (i.e., thermotherapy and chemotherapy), as compared to the individual therapy (i.e., thermotherapy or chemotherapy) using the SPIONs/Cur/Ver loaded PLGA NPs. Thus, the as-prepared SPIONs/dual-drugs co-loaded PLGA NPs (i.e., MMPNs based ferrofluids) are potential therapeutic candidates for multi-modal treatment of cancer in vitro using thermotherapy and chemotherapy
Unraveling the Role of Silent Mutation in the omega-Subunit of Escherichia coli RNA Polymerase: Structure Transition Inhibits Transcription
No full textThe bacterial RNA polymerase is a multi-subunit enzyme complex composed of six subunits, alpha(2)beta beta'sigma omega. The function of this enzyme is to transcribe the DNA base sequence to the RNA intermediate, which is ultimately translated to protein. Though the contribution of each subunit in RNA synthesis has been clearly elucidated, the role of the smallest omega-subunit is still unclear despite several studies. Recently, a study on a dominant negative mutant of rpoZ has been reported in which the mutant was shown to render the RNA polymerase defective in transcription initiation (omega(6), N60D) and gave an insight on the function of omega in RNA polymerase. Serendipitously, we also obtained a silent mutant, and the mutant was found to be lethal during the isolation of toxic mutants. The primary focus of this study is to understand the mechanistic details of this lethality. Isolated omega shows a predominantly unstructured circular dichroism profile and becomes alpha-helical in the enzyme complex. This structural transition is perhaps the reason for this lack of function. Subsequently, we generated several silent mutants of omega to investigate the role of codon bias and the effect of rare codons with respect to their position in rpoZ. Not all silent mutations affect the structure. RNA polymerase when reconstituted with structurally altered silent mutants of omega is transcriptionally inactive. The CodonPlus strain, which has surplus tRNA, was used to assess for the rescue of the phenotype in lethal silent mutants