Higher-point conformal blocks and entanglement entropy in heavy states

We consider conformal blocks of two heavy operators and an arbitrary number of light operators in a (1+1)-d CFT with large central charge. Using the monodromy method, these higher-point conformal blocks are shown to factorize into products of 4-point conformal blocks in the heavy-light limit for a class of OPE channels. This result is reproduced by considering suitable worldline configurations in the bulk conical defect geometry. We apply the CFT results to calculate the entanglement entropy of an arbitrary number of disjoint intervals for heavy states. The corresponding holographic entanglement entropy calculated via the minimal area prescription precisely matches these results from CFT. Along the way, we briefly illustrate the relation of these conformal blocks to Riemann surfaces and their associated moduli space.Comment: 41 pages, 10 figures. (Published version; typos corrected and references added.

2D materials based nanopore structures as single molecule sensors

Nanopores are impedance based bio-sensors. The principle of nanopore sensors is analogous to that of a Coulter counter. A nanoscale aperture (the nanopore) is formed in an insulating membrane separating two chambers filled with conductive electrolyte. Charged molecules are driven through the pore under an applied electric voltage (a process known as electrophoresis), thereby modulating the ionic current through the nanopore. The temporary modulation of ionic current due to translocation of the molecule provides useful information about the structure, length, orientation and sequence. This versatile approach permits the label-free, amplification-free analysis of charged biopolymers. The major challenges facing nanopore based techniques for practical sequencing applications are the limitations on temporal and spatial resolution. The finite thickness of membranes limit the spatial resolution of the measurement as multiple nucleotides occupy the pore at a given instant, reducing the sensitivity of the signal making single nucleotide resolution difficult to achieve. Graphene and MoS¬2 as a single layer material of the same order of thickness as the nucleotide separation in a DNA strand presents an exciting alternative to commercial Silicon nitride membranes. These materials also provide potential for exploration of field effect mechanisms which can be an alternative mechanism detect the individual nucleotides in the DNA strand. The possibility and feasibility of using the unique electrical properties of embedded active layers of graphene and MoS2 in stacked membranes has been explored here. The embedded graphene layers presented unique insights into the electrochemical properties of graphene edges in an embedded nanopore structure. The lack of a bad gap in graphene (unless extremely narrow constrictions are fabricated, which is very challenging) makes MoS2 (monolayers have a direct band gap of 1.85 eV) the more favorable material for charge based detection. The electrical properties of both graphene and MoS2 channels are reported here. Additionally we also studied the DNA transport through nanopores in freely suspended MoS2 membranes as well as integration of MoS2 in our stacked architecture. The other major challenge is to control/slow down DNA transport to within bandwidth limitation of commercial instruments to ensure reliable nucleotide separation in the blockade signal. The application of graphene-DNA hydrophobic attractions as a method to reduce DNA translocation speed is reported. A final device with integrated graphene, MoS2 and dielectric layers could provide the required structure to achieve DNA sequencing. In addition atomic layer thin membranes could also improve the diagnostic capabilities of nanopore detection. The atomic layer thickness of these membranes could enable spatial mapping of size differences of an individual molecule. We report the ability of MoS2 membrane to distinguish free DNA from DNA-protein complex molecules. The ability to detect the presence of methyl binding domain proteins on methylated sites of DNA is valuable to the field of cancer diagnostics and such thin membranes could provide a pathway for spatial mapping of individual methylated sites

Tip-Based Nanofabrication of Arbitrary Shapes of Graphene Nanoribbons for Device Applications

Graphene nanoribbons (GNRs) have promising applications in future nanoelectronics, chemical sensing and electrical interconnects. Although there are quite a few GNR nanofabrication methods reported, a rapid and low-cost fabrication method that is capable of fabricating arbitrary shapes of GNRs with good-quality is still in demand for using GNRs for device applications. In this paper, we present a tip-based nanofabrication method capable of fabricating arbitrary shapes of GNRs. A heated atomic force microscope (AFM) tip deposits polymer nanowires atop a CVD-grown graphene surface. The polymer nanowires serve as an etch mask to define GNRs through one step of oxygen plasma etching similar to photoresist in conventional photolithography. Various shapes of GNRs with either linear or curvilinear features are demonstrated. The width of the GNR is around 270 nm and is determined by the width of depositing polymer nanowire, which we estimate can be scaled down 15 nms. We characterize our TBN-fabricated GNRs using Raman spectroscopy and I-V measurements. The measured sheet resistances of our GNRs fall within the range of 1.65 kΩ - 2.64 kΩ-1 in agreement with previously reported values. Furthermore, we determined the high-field breakdown current density of GNRs to be approximately 2.94x108 A/cm2. This TBN process is seamlessly compatible with existing nanofabrication processes, and is particularly suitable for fabricating GNR based electronic devices including next generation DNA sequencing technologies and beyond silicon field effect transistors

Climate change, migration and adaptation in deltas Key findings from the DECCMA projet

This work was carried out under the Collaborative Adaptation Research Initiative in Africa and Asia (CARIAA), with financial support from the UK Government’s Department For International Development (DFID) and the International Development Research Centre (IDRC), Canada.Deltas are home to 500 million people worldwide and known as a climate hange “hotspot” – a place where high exposure to climate stresses coincides with high levels of vulnerability. DECCMA has been undertaking research on climate and environmental change, migration and adaptation in three delta ystems: the transboundary Ganges-Brahmaputra-Meghna megadelta (comprising the Indian Bengal delta, as well as the bulk in Bangladesh), the Mahanadi delta in India, and the Volta in Ghana

Gadolinium(III)-Based Porous Luminescent Metal-Organic Frameworks for Bimodal Imaging

Gd-III-based metal-organic frameworks, Gd-pDBI-1 and Gd-pDBI-2, have been synthesized using the linker pDBI (pDBI=1,4-bis(5-carboxy-1H-benzimidazole-2yl)benzene). They exhibited structural diversity due to subtle change in reaction constituents. Owing to the judicious choice of the fluorescent linker, the materials could be used for bimodal imaging (fluorescent and magnetic resonance) and displayed a modest T1 relaxivity value

Power-laws in dog behavior may pave the way to predictive models: A pattern analysis study

Apparently random events in nature often reveal hidden patterns when analyzed using diverse and robust statistical tools. Power law distributions, for example, project diverse natural phenomenon, ranging from earthquakes to heartbeat dynamics into a common platform of self-similarity. Animal behavior in specific contexts has been shown to follow power law distributions. However, the behavioral repertoire of a species in its entirety has never been analyzed for the existence of such underlying patterns. Here we show that the frequency-rank data of randomly sighted behaviors at the population level of free-ranging dogs follow a scale-invariant power law behavior. It suggests that irrespective of changes in location of sightings, seasonal variations and observer bias, datasets exhibit a conserved trend of scale invariance. The data also exhibits robust self-similarity patterns at different scales which we extract using multifractal detrended fluctuation analysis. We observe that the probability of consecutive occurrence of behaviors of adjacent ranks is much higher than behaviors widely separated in rank. The findings open up the possibility of designing predictive models of behavior from correlations existing in true time series of behavioral data and exploring the general behavioral repertoire of a species for the presence of syntax