On transport in quantum Hall systems with constrictions

Motivated by recent experimental findings, we study transport in a simple phenomenological model of a quantum Hall edge system with a gate-voltage controlled constriction lowering the local filling factor. The current backscattered from the constriction is seen to arise from the matching of the properties of the edge-current excitations in the constriction ($\nu_{2}$) and bulk ($\nu_{1}$) regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model, finding that a competition between two tunneling process, related by a quasiparticle-quasihole symmetry, determines the fate of the low-bias transmission conductance. In this way, we find satisfactory explanations for many recent puzzling experimental results.Comment: 4 pages, 4 figure

GMRT observations of X-shaped radio sources

We present results from a study of X-shaped sources based on observations using the Giant Metrewave Radio Telescope (GMRT). These observations were motivated by our low frequency study of 3C 223.1 (Lal & Rao 2005), an X-shaped radio source, which showed that the wings (or low-surface-brightness jets) have flatter spectral indices than the active lobes (or high-surface-brightness jets), a result not easily explained by most models. We have now obtained GMRT data at 240 and 610 MHz for almost all the known X-shaped radio sources and have studied the distribution of the spectral index across the sources. While the radio morphologies of all the sources at 240 and 610 MHz show the characteristic X-shape, the spectral characteristics of the X-shaped radio sources, seem to fall into three categories, namely, sources in which (A) the wings have flatter spectral indices than the active lobes, (B) the wings and the active lobes have comparable spectral indices, and (C) the wings have steeper spectral indices than the active lobes. We discuss the implications of the new observational results on the various formation models that have been proposed for X-shaped sources.Comment: The paper contains 12 figures and 3 tables, accepted for publication in MNRAS Main Journal, please note, some figures are of lower qualit

Experimental Study of Cement Mortar Incorporating Pond Ash with Elevated Temperature Exposure

Pond ash is to be investigated for its use as a partial replacement for sand in cement mortar (1:4). The effort is to be made for the utilization of Pond Ash as sand replacement material in mortar which may introduces many benefits from economical, technical and environmental points of view. The project will present the results of the cement mortar of mix proportion 1:4 in which sand will partially replace with Pond Ash as 0%, 10%, 30%, 40% and 50% by weight of sand. It is proposed to prepare two set of mixture proportions. First will be a control mix (without Pond Ash with regional fine aggregate (sand) and the other mixing will contain Pond Ash obtained from Thermal Power plant industry. The compressive strength test is to be conducted with partial replacement of Pond Ash with sand. The strength property of mortar with Pond Ash for strength at 28 days as partial replacement with the cement in the cement mortar 1:4 is to be determined. Similarly the other set of cement mortar incorporating Pond Ash is to be kept in elevated temperature up to 1100° C and tested for its compressive strength. The results for controlled cement mortar and Pond Ash mortar for compressive strength at normal temperature and elevated temperature is to be compare

The use of orbitals and full spectra to identify misalignment

In this paper, a SpectraQuest demonstrator is used to introduce misalignment in a rotating set-up. The vibrations caused by misalignment is measured with both accelerometers on the bearings and eddy current probes on the shaft itself. A comparison is made between the classical spectral analysis, orbitals and full spectra. Orbitals are used to explain the physical interpretation of the vibration caused by misalignment. Full spectra allow to distinguish unbalance from misalignment by looking at the forward and reversed phenomena. This analysis is done for different kinds of misalignment, couplings, excitation forces and combined machinery faults

CONFLLVM: A Compiler for Enforcing Data Confidentiality in Low-Level Code

We present an instrumenting compiler for enforcing data confidentiality in low-level applications (e.g. those written in C) in the presence of an active adversary. In our approach, the programmer marks secret data by writing lightweight annotations on top-level definitions in the source code. The compiler then uses a static flow analysis coupled with efficient runtime instrumentation, a custom memory layout, and custom control-flow integrity checks to prevent data leaks even in the presence of low-level attacks. We have implemented our scheme as part of the LLVM compiler. We evaluate it on the SPEC micro-benchmarks for performance, and on larger, real-world applications (including OpenLDAP, which is around 300KLoC) for programmer overhead required to restructure the application when protecting the sensitive data such as passwords. We find that performance overheads introduced by our instrumentation are moderate (average 12% on SPEC), and the programmer effort to port OpenLDAP is only about 160 LoC.Comment: Technical report for CONFLLVM: A Compiler for Enforcing Data Confidentiality in Low-Level Code, appearing at EuroSys 201

Transport through constricted quantum Hall edge systems: beyond the quantum point contact

Motivated by surprises in recent experimental findings, we study transport in a model of a quantum Hall edge system with a gate-voltage controlled constriction. A finite backscattered current at finite edge-bias is explained from a Landauer-Buttiker analysis as arising from the splitting of edge current caused by the difference in the filling fractions of the bulk ($\nu_{1}$) and constriction ($\nu_{2}$) quantum Hall fluid regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model. The constriction region splits the incident long-wavelength chiral edge density-wave excitations among the transmitting and reflecting edge states encircling it. The competition between two interedge tunneling processes taking place inside the constriction, related by a quasiparticle-quasihole (qp-qh) symmetry, is accounted for by computing the boundary theories of the system. This competition is found to determine the strong coupling configuration of the system. A separatrix of qp-qh symmetric gapless critical states is found to lie between the relevant RG flows to a metallic and an insulating configuration of the constriction system. This constitutes an interesting generalisation of the Kane-Fisher quantum impurity model. The features of the RG phase diagram are also confirmed by computing various correlators and chiral linear conductances of the system. In this way, our results find excellent agreement with many recent puzzling experimental results for the cases of $\nu_{1}=1/3,~1$. We also discuss and make predictions for the case of a constriction system with $\nu_{2}=5/2$.Comment: 18 pages, 9 figure