Archives—August 2013

Janarjan Bhandari Research

Janarjan Bhandari Experiment
Experimental setup for the study of the CO2 band using a tunable diode laser.

I am a graduate student working under Dr. Claudio Mazzoleni in the Environmental Optics Laboratory (EOL) at Michigan Tech. Currently I am studying the absorption spectra of water vapor to determine the appropriate transition lines suitable for my experiment. Water vapor is a critical gas present in the atmosphere in variable amounts that absorbs in various wavelength regions from the far infrared to the UV region. This results in hundreds of band spectra and thousands of transition lines. I am using the HITRAN database to simulate and select the optimal lines for my study using a Tunable Diode Laser. I am working to develop an instrument that can monitor the water vapor concentration in the Cloud chamber soon to be installed at Michigan Tech. Before stepping into this experiment, I studied the absorption band of CO2 using a tunable diode laser.

I have also been working on the development of a Quartz-Enhanced Photoacoustic Spectroscopy system. A piezo-electric quartz tuning fork has been successfully utilized in photoacoustic spectroscopy in a gas filled resonator for the study of light absorption by gases. Our group is determined to extend this technique to measure aerosol absorption in real world situations.

by Janarjan Bhandari

References:

Reliable optical measurement of water vapor in highly scattering environment, Park et.al (2009) Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Quartz-enhanced photoacoustic spectroscopy, Kosterev et.al (2002) Optics Letters




Douglas Banyai Research

Doug Banyai Computer Model
Computer model of a nanoparticle based transistor. The conduction channel consists of a disordered array of nanoparticles. This model is used with the finite element method to investigate capacitances.

Mutli-scale modeling of nanoparticle based transistors

For half a century the integrated circuits (ICs) that make up the heart of electronic devices have been steadily improving by shrinking at an exponential rate. However, as the current crop of ICs get smaller and the insulating layers involved become thinner, electrons leak through due to quantum mechanical tunneling. This is one of several issues which will bring an end to the party, after which future improvements will have to come from employing fundamentally different transistor architecture rather than fine tuning and miniaturizing the field effect transistors in use today.

Several new transistor designs, some designed and built here at Tech, involve electrons tunneling their way through arrays of nanoparticles. We use a multi-scale approach to model these devices and study their behavior. For the smallest details of how often electrons jump from one particular nanoparticle to another, we use a first principles approach (density functional theory) to study the quantum mechanics involved. To estimate the change in energy due to the movement of a single electron, we use the finite element method to calculate electrostatic capacitances. The kinetic Monte Carlo method allows us to use our knowledge of these details to simulate an entire device — sometimes consisting of hundreds of individual particles — and watch as a device ‘turns on’ and starts conducting an electric current. Finally, we are developing new algorithms that will allow us to simulate the collective behavior of thousands of devices.

This work is ongoing under the advisement of Dr. John Jaszczak, in collaboration with the research groups of Dr. Pandey, Dr. Bergstrom, and Dr. Yap, and with support from the Miles fellowship.

Doug Banyai 2 Clusters
Model of of two gold nanoparticles at atomic resolution. This model is used to investigate tunneling between nanoparticles.


Ravi Joshi Research

Ravi Joshi
Ravi Joshi

How would negative energy density affect a classic Friedmann cosmology? Although never measured and possibly unphysical, the evolution of a universe containing a significant cosmological abundance of any of a number of hypothetical stable negative energy components is explored. These negative energy (Omega < 0) forms include negative phantom energy (w<-1), negative cosmological constant w=-1, negative domain walls w=-2/3, negative cosmic strings (w=-1/3), negative mass w=0, negative radiation (w=1/3), and negative ultra light (w > 1/3). Assuming that such universe components generate pressures as perfect fluids, the attractive or repulsive nature of each negative energy component is reviewed.

The Friedmann equations can only be balanced when negative energies are coupled to a greater magnitude of positive energy or positive curvature, and minimal cases of both of these are reviewed. The future and fate of such universes in terms of curvature, temperature, acceleration, and energy density are reviewed including endings categorized as a Big Crunch, Big Void, or Big Rip and further qualified as “Warped”, “Curved”, or “Flat”, “Hot” versus “Cold”, “Accelerating” versus “Decelerating” versus “Coasting”. A universe that ends by contracting to zero energy density is termed a Big Poof. Which contracting universes “bounce” in expansion and which expanding universes “turnover” and contract are also reviewed.


Hao Zhou Research

HAWC Experiment
Figure 1: The HAWC experiment as of July 26, 2013. The full array will cover the whole plane in the center of the picture.

I am working with Dr. Petra Huentemeyer on the HAWC (short for High Altitude Water Cherenkov) experiment, a very high energy (VHE) gamma-ray observatory currently being built in Mexico. In contrast to optical or radio waves, gamma-ray photons cannot penetrate the Earth’s atmosphere. Instead they collide with particles in the atmosphere and create showers of secondary particles through electromagnetic and hadronic interactions. Once completed the HAWC experiment will consist of 300 water Cherenkov detectors (WCDs), that will measure these secondary particles as they sweep through the array. The directions of the primary gamma-ray photons are reconstructed using the time between the signals in each WCD. Thus timing calibration, which is what I am currently working on, is crucial for good angular resolution. As of now, more than one third of the array is finished and operational. At the moment, I am doing a preliminary analysis of data collected with this sub-array. Figure 1 shows a picture of HAWC on July 26, 2013. My research is focusing on pulsar wind nebulae (PWNe), the largest class of galactic VHE gamma-ray sources. PWNe produce electromagnetic radiation in a very broad energy range from radio to VHE gamma rays, and thereby provide an excellent laboratory to study the physical processes at very high energy. Figure 2 shows the crab nebula at different wavelengths. Using data collected with the complete HAWC array, I will reconstruct the energy spectrum of gamma rays emitted by PWNe. I will combine my analysis results with data from other experiments that take measurements at lower energies, to reveal the physics processes occurring in PWNe.

by Hao Zhou

Crab Nebula
Figure 2: Crab nebula in radio (red), optical (green) and X-ray (blue) from APOD (Astronomy Picture of the Day) on September 20, 2002. Credit: J. Hester (ASU), CXC, HST, NRAO, NSF, NASA

SURF Presentations August 12 and 13, 2013

Recipients of Summer Undergraduate Research Fellowships (SURFs) will present end-of-summer project updates Monday and Tuesday (Aug. 12 and 13), from 9 to 11 a.m., in Fisher 139.

From Tech Today.

SURF award recipients in physics include:

Joseph Charnawskas
Advisor: Raymond Shaw
The Effects of the Gravitational Force on Water Particles in a Turbulent Flow

Mick Small
Advisor: Yoke Khin Yap
Photovoltaic Responses of Quantum Dot Sensitized ZnO Nanowires

Angela Small (Honor’s Institute)
Advisor: Jacek Borysow
Analysis of Artificial Breath Samples Using Raman Spectroscopy for Medical Diagnosis

Kevin Rocheleau (Honor’s Institute)
Advisor: Petra Huentemeyer
Analysis and Modeling of Diffuse Gamma-Ray Emission from the Cygnus Region using FERMI and HAWC Data