arXiv subjects

Mitra Djamal

Publications and source records attributed to Mitra Djamal.

9 recordsLinked to original sources

arXiv2019

An experiment to search for dark matter interactions using sodium iodide detectors

Observations of galaxies and primordial radiation suggest that the Universe is made mostly of non-luminous dark matter. Several types of new fundamental particles have been proposed as candidates for dark matter such as weakly interacting massive particles (WIMPs) but no definitive signal has been seen despite concerted efforts by many collaborations. One exception is the much-debated claim by the DAMA collaboration of a statistically significant annual modulation in the event rate of their experiment with a period and phase consistent with that expected from WIMP dark matter. Several groups have been working to develop experiments with the aim of reproducing DAMA's results using the same target medium. Here we report results from the initial operation of the COSINE-100 experiment. COSINE-100 uses sodium iodide as the target medium-the same medium as DAMA-and is designed to carry out a model-independent test of DAMA's claim. Initial data based on the first 59.5 days indicate that there is no excess of events over the expected background, confirming that DAMA's annual modulation signal is in severe tension with results from other experiments under the assumption of dark matter having spin independent interactions and the Standard Halo Model. COSINE-100 is now taking data to study the presence of dark matter-induced annual modulation in the event rate of the sodium iodide detectors.

astro-ph.IM↗

arXiv2018

Statistical Improvement in Detection Level of Gravitational Microlensing Events from their Light Curves

In Astronomy, the brightness of a source is typically expressed in terms of magnitude. Conventionally, the magnitude is defined by the logarithm of the received flux. This relationship is known as the Pogson formula. For received flux with a small signal to noise ratio (S/N), however, the formula gives a large magnitude error. We investigate whether the use of Inverse Hyperbolic Sine function (after this referred to as the Asinh magnitude) in the modified formulae could allow for an alternative calculation of magnitudes for small S/N flux, and whether the new approach is better for representing the brightness of that region. We study the possibility of increasing the detection level of gravitational microlensing using 40 selected microlensing light curves from 2013 and 2014 season and by using the Asinh magnitude. The photometric data of the selected events is obtained from the Observational Gravitational Lensing Experiment (OGLE). We found that the utilization of the Asinh magnitude makes the events brighter compared to using the logarithmic magnitude, with an average of about $3.42 \times10^{-2}$ magnitude and the average of the difference of error between the logarithmic and the Asinh magnitude is about $2.21 \times10^{-2}$ magnitude. The microlensing events, OB 140847 and OB 140885 are found to have the largest difference values among the selected events. Using a Gaussian fit to find the peak for OB140847 and OB140885, we conclude statistically that the Asinh magnitude gives better mean squared values of the regression and narrower residual histograms than the Pogson magnitude. Based on these results, we also attempt to propose a limit of magnitude value from which the use of the Asinh magnitude is optimal for small S/N data.

astro-ph.IM↗

arXiv2015

Multi-wavelength Fibril Dynamics and Oscillations Above Sunspot - I. Morphological Signature

In this work we selected one particular fibril from a high resolution solar chromosphere observation from the Dutch Open Telescope, and tried to obtain a broad picture of the intricate mechanism that might be incorporated in the multiple layer of the Solar atmosphere in high cadence multi-wavelength observation. We analyzed the changingvfibril patter using multi-wavelength tomography, which consists of both H$α$ line center \& the blue wing, Doppler-signal, Ca II H, and the G-band. We have found that the intermittent ejected material through fibril from Doppler images has clearly shown oscillation mode, as seen in the H$α$ blue wing. The oscillations in the umbrae and penumbrae magnetic field lines that are above the sunspot cause a broadening and forms the area like a ring shape from 3 to 15-minute oscillations as function of height. These made a distinct boundary of umbrae and penumbrae which suggest the comb structure, and indicate that the oscillations could propagate along the inclined magnetic flux tubes from below. The 3-minute strongly appeared in the broadly inclined penumbrae magnetic filed lines and gave the clear light-bridge. The well known 5-minute was dominated in the umbrae-penumbrae region boundary, the long 7-minute one was transparent in the H$α$ blue wing, but this was the same with 10 and 15-minute, it was concentrated in the inner-penumbrae, as seen in the H$α$ line center. From these findings we propose a picture on the role of fibril as the fabric of interaction between the layers, also the related activites around the active region under investigation.

astro-ph.SR↗

arXiv2014

Lup-Like Cantilever Beam for Small Deflection

A lup-like cantilever beam are discussed in this work. For small deflection it can be approximated as a spring-mass system with certain spring constant whose effective mass is larger than the usual constant rectangular cross section cantilever beam. A new parameter $β$ is introduced to relates some the properties of lup-like cantilever beam to the usual one. Influence of beam witdh $B_0$ and head width $B_t$ to value of $β$ is also presented.

physics.ins-det↗

arXiv2014

Measuring Quasi-Static and Kinetic Coefficient of Restitution Simultaneously using Levitation Mass Method: Experiment and Simulation

Observed peaks in a levitation mass method (LMM), which are usually addressed to signal noise, are discussed in this work. This phenomenon arises due to bounce from plate which is collided by moving part in LMM measurement system. Normally, the moving part and the plate stick very good after their first contact. Simulation using molecular dynamics (MD) method is performed to prove the bounce prognosis.

physics.ins-det↗

arXiv2013

Novel Giant Magnetoresistance Model using Multiple Barrier Potential

This paper proposes a new model for Giant Magnetoresistance (GMR) and calculates its typical graph qualitatively. The model foundation is the microscopic mechanism in GMR, where the GMR effect can be explained by intrinsic and extrinsic potential. The potentials are spin-dependent. The potentials determine the transmission probability then it will give conductance value. Here, the multiple barrier potential model is proposed as the new GMR model. The transmission probability is determined using transfer matrix method. It was found that this model is fit qualitatively with the typical GMR graph.

cond-mat.mtrl-sci↗

arXiv2011

Competition between Thickness and Electrical Conditioning Influence in Enhancing Giant Magnetoresistance Ratio for NiCoFe/Alq3/NiCoFe Spin Valve

Spacer thickness and electrical conditioning have their own influence in enhancing giant magnetoresistance (GMR) ratio. At some condition one factor can override the other as reported by experiment results. An empiric model about competition about these two factors is discussed in this work. Comparison from experiment results to validate the model are also shown and explained. A formulation is proposed to extend the existing one that now accommodates both spacer thickness and electrical conditioning in one form.

cond-mat.mes-hall↗

arXiv2011

Failure of Numerical modeling of 3-D Position Reconstruction from 3-Axial Planar Spiral Coil Sensor Sensitivity due to Existence of Quadratic Terms

A sensitivity profile of a planar spiral coil sensor (PSCS) is proposed and is used to generate the relation of 3-D position of object observed using three PSCSs, one in each x, y, and z axis to the sensors response. A numerical procedure using self consistent field-like method to reconstruct the real position of observed object from sensor sensitivity is presented and the results are discussed. Unfortunately, the procedure fails to approach the desired results due to the existence of quadratic terms.

physics.data-an↗

arXiv2011

Giant Magnetoresistance Effect in Organic Material and Its Potential for Magnetic Sensor

Giant magnetoresistance (GMR) material has great potential as next generation magnetic field sensing devices, have magnetic properties and high electrical potential to be developed into various applications such as: magnetic field sensor measurements, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory (MRAM). Today, the new GMR materials based on organic material obtained after allowing for Organic Magnetoresistance (OMAR) was found in OLEDs (organic light-emitting diodes). This organic material is used as a spacer layer in GMR devices with spin-valve structures. Traditionally, metals and semiconductors are used as a spacer layer in spin-valve. However, several factors such as spin scattering caused by large atoms of the spacer material and the interface scattering of ferromagnetic with a spacer, will limit the efficiency of spin-valve. In this paper, we describe a new GMR materials based on organic material that we have developed.

cond-mat.mes-hall↗