1,630 research outputs found
Soft Carrier Multiplications by Hot Electrons in Graphene
By using Boltzmann formalism, we show that carrier multiplication by impact
ionization can take place at relatively low electric fields during electronic
transport in graphene. Because of the absence of energy gap, this effect is not
characterized by a field threshold unlike in conventional semiconductors, but
is a quadratic function of the electric field. We also show that the resulting
current is an increasing function of the electronic temperature, but decreases
with increasing carrier concentration
POSE ESTIMATION AND 3D RECONSTRUCTION USING SENSOR FUSION
A camera maps 3-dimensional (3D) world space to a 2-dimensional (2D) image space. In the process it loses the depth information, i.e., the distance from the camera focal point to the imaged objects. It is impossible to recover this information from a single image. However, by using two or more images from different viewing angles this information can be recovered, which in turn can be used to obtain the pose (position and orientation) of the camera. Using this pose, a 3D reconstruction of imaged objects in the world can be computed. Numerous algorithms have been proposed and implemented to solve the above problem; these algorithms are commonly called Structure from Motion (SfM). State-of-the-art SfM techniques have been shown to give promising results. However, unlike a Global Positioning System (GPS) or an Inertial Measurement Unit (IMU) which directly give the position and orientation respectively, the camera system estimates it after implementing SfM as mentioned above. This makes the pose obtained from a camera highly sensitive to the images captured and other effects, such as low lighting conditions, poor focus or improper viewing angles. In some applications, for example, an Unmanned Aerial Vehicle (UAV) inspecting a bridge or a robot mapping an environment using Simultaneous Localization and Mapping (SLAM), it is often difficult to capture images with ideal conditions. This report examines the use of SfM methods in such applications and the role of combining multiple sensors, viz., sensor fusion, to achieve more accurate and usable position and reconstruction information.
This project investigates the role of sensor fusion in accurately estimating the pose of a camera for the application of 3D reconstruction of a scene. The first set of experiments is conducted in a motion capture room. These results are assumed as ground truth in order to evaluate the strengths and weaknesses of each sensor and to map their coordinate systems. Then a number of scenarios are targeted where SfM fails. The pose estimates obtained from SfM are replaced by those obtained from other sensors and the 3D reconstruction is completed. Quantitative and qualitative comparisons are made between the 3D reconstruction obtained by using only a camera versus that obtained by using the camera along with a LIDAR and/or an IMU. Additionally, the project also works towards the performance issue faced while handling large data sets of high-resolution images by implementing the system on the Superior high performance computing cluster at Michigan Technological University
Superconductivity at 5K in NdO0.5F0.5BiS2
We report appearance of superconductivity at 5K in NdO0.5F0.5BiS2 and
supplement the discovery [1] of the same in layered sulfide based ZrCuSiAs type
compounds. The bulk polycrystalline compound is synthesized by conventional
solid state route via vacuum encapsulation technique. Detailed structural
analysis showed that the studied compound is crystallized in tetragonal P4/nmm
space group with lattice parameters a = 3.9911(3) {\AA}, c = 13.3830(2) {\AA}.
Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5K by both transport
and magnetic measurements. Electrical transport measurements showed
superconducting Tc onset at 5.2K and Tc ({\rho}=0) at 4.7K. Under applied
magnetic field both Tc onset and Tc ({\rho} =0) decrease to lower temperatures
and an upper critical field [Hc2(0)] of above 23kOe is estimated. Both AC and
DC magnetic susceptibility measurements showed bulk superconductivity below 5K.
Isothermal magnetization (MH) exhibited typical type II behavior with lower
critical field (Hc1) of around 15Oe. Isothermal magnetization (MH) exhibited
typical type-II behavior with lower critical field (Hc1) of around 15Oe.
Specific heat [Cp(T)] is investigated in the temperature range of 1.9-50K in
zero external magnetic field. A Schottky-type anomaly is observed at low
temperature below 7K. This low temperature Schottky can be attributed to the
change in the entropy of the system.Comment: 10 pages text + Figs (New Version):comments/suggestion welcome
([email protected]
Synthesis and superconductivity of new BiS2 based superconductor PrO0.5F0.5BiS2
We report synthesis and superconductivity at 3.7K in PrO0.5F0.5BiS2. The
newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2
compounds having ZrCuSiAs type structure. The bulk polycrystalline compound is
synthesized by vacuum encapsulation technique at 7800C in single step. Detailed
structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is
crystallized in tetragonal P4/nmm space group with lattice parameters a =
4.015(5) {\AA}, c = 13.362(4) {\AA}. Bulk superconductivity is observed in
PrO0.5F0.5BiS2 below 4K from magnetic and transport measurements. Electrical
transport measurements showed superconducting transition temperature (Tc) onset
at 3.7K and Tc ({\rho}=0) at 3.1K. Hump at Tc related to superconducting
transition is not observed in heat capacity measurement and rather a
Schottky-type anomaly is observed at below ~6K. The compound is slightly
semiconducting in normal state. Isothermal magnetization (MH) exhibited typical
type II behavior with lower critical field (Hc1) of around 8Oe.Comment: Short note 10 pages text+figs. First report on PrO.5F.5BiS2 Su
Crossing point phenomena (T* = 2.7 K) in specific heat curves of superconducting ferromagnets RuSr2Gd1.4Ce0.6Cu2O10-{\delta}
Crossing point phenomena are one of the interesting and still puzzling
effects in strongly correlated electron systems. We have synthesized
RuSr2Gd1.4Ce0.6Cu2O10-{\delta} (GdRu-1222) magneto-superconductor through
standard solid state reaction route and measured its magnetic, transport and
thermal properties. We also synthesized RuSr2Eu1.4Ce0.6Cu2O10-{\delta}
(EuRu-1222) then measured its heat capacity in zero magnetic fields for
reference. The studied compounds crystallized in tetragonal structure with
space group I4/mmm. GdRu-1222 is a reported magneto-superconductor with Ru
spins magnetic ordering at temperature around 110 K and superconductivity in
Cu-O2 planes below around 40 K. To explore the crossing point phenomena, the
specific heat [Cp (T)] was investigated in temperature range 1.9-250 K, under
magnetic field of up to 70 kOe. Unfortunately though no magnetic and
superconducting transitions are observed in specific heat, a Schottky type
anomaly is observed at low temperatures below 20 K. This low temperature
Schottky type anomaly can be attributed to splitting of the ground state
spectroscopic term 8S7/2 of paramagnetic Gd3+ ions by both internal and
external magnetic fields. It was also observed that Cp (T) being measured for
different values of magnetic field, possesses the same crossing point (T* = 2.7
K), up to the applied magnetic field 70 kOe. A quantitative explanation of this
phenomenon, based on its shape and temperature dependence of the associated
generalized heat capacity (Cp), is presented. This effect supports the crossing
point phenomena, which is supposed to be inherent for strongly correlated
systems.Comment: 12 pages Text+Figs ([email protected]
Study of Thyroid Lesions by Fine Needle Aspiration Cytology and its Correlation with Thyroid Function Test
Introduction: Fine needle aspiration cytology (FNAC) of the thyroid gland has been widely and successfully utilized for diagnosis. Assessment of thyroid pathology is even more informative if correlated with thyroid function tests (TFT). This study aims to compare the efficacy of fine needle aspiration cytology with thyroid function tests in different thyroid lesions.
Methods: A descriptive study was carried out among the patients who presented with thyroid swellingvisiting Department of Ear Nose Throat (ENT) of Lumbini Medical College and Teaching Hospital (LMCTH) fromJune 2012 to February 2013. The study population were selected on random basis. A total of fifty patients involved in the study and were sent to Department of Pathology for FNAC and TFT.
Results: Most of the cases (44%) of thyroid swelling were from 21 to 40 years of age. Among them, 86% were females. Out of total respondents, 48% were found to be colloid goiter. 70% findings of FNAC and TFT were in accordance.
Conclusions: The findings of FNAC and TFT were found to be significantly associated (P value <0.05)
Bulk Superconductivity in Bismuth-oxy-sulfide Bi4O4S3
Very recent report [1] on observation of superconductivity in Bi4O4S3 could
potentially reignite the search for superconductivity in a broad range of
layered sulphides. We report here synthesis of Bi4O4S3 at 5000C by vacuum
encapsulation technique and basic characterizations. Detailed structural,
magnetization, and electrical transport results are reported. Bi4O4S3 is
contaminated by small amounts of Bi2S3 and Bi impurities. The majority phase is
tetragonal I4/mmm space group with lattice parameters a = 3.9697(2){\AA}, c =
41.3520(1){\AA}. Both AC and DC magnetization measurements confirmed that
Bi4O4S3 is a bulk superconductor with superconducting transition temperature
(Tc) of 4.4K. Isothermal magnetization (MH) measurements indicated closed loops
with clear signatures of flux pinning and irreversible behavior. The lower
critical field (Hc1) at 2K, of the new superconductor is found to be ~39 Oe.
The magneto-transport R(T, H) measurements showed a resistive broadening and
decrease in Tc (R=0) to lower temperatures with increasing magnetic field. The
extrapolated upper critical field Hc2(0) is ~ 310kOe with a corresponding
Ginzburg-Landau coherence length of ~100{\AA} . In the normal state the {\rho}
~ T2 is not indicated. Our magnetization and electrical transport measurements
substantiate the appearance of bulk superconductivity in as synthesized
Bi4O4S3. On the other hand same temperature heat treated Bi is not
superconducting, thus excluding possibility of impurity driven
superconductivity in the newly discovered Bi4O4S3 superconductor.Comment: 12 pages Text + Fig
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