Session D42: SPS Undergraduate Research II

A mathematical model for late term cancer chemotherapy

A mathematical model for cancer treated with the ``on-off'' type where the drug is either active or inactive and when the chemotherapeutic treatment only affects the cycling cells is presented. This model is considered for late term chemotherapy when the total population of cells doesn't show a significant change. The size of the cycling cells as a function of time has been investigated.   

Real Time Observation of DNA Nanotube Assembly

DNA nanotubes are of interest for applications ranging from nanofabrication to biophysical studies. The DNA Nanotubes used in this research are self-assembling structures composed of DNA double-crossover tiles. These tiles are simply two connected helices composed of five single stranded DNA oligomers. Each tile exposes four sticky ends responsible for the linkage between neighboring tiles. This linkage creates the nanotube lattice, with intrinsic curvature. The curvature orients each tile with a 60$^{o}$ angle from the previous one so that six tiles make up the circumference of a nanotube. Nanotube stability depends on conditions such as ionic strength and temperature. A PCR machine is used to anneal the strands into nanotubes. A duplicated annealing process was constructed under a light microscope. PVP (polyvinyl prolidone) coated glass both confined the DNA nanotubes to a 2-3 $\mu $m focal plane and prevented them from sticking to the sample surface. By the time the tubes were long enough to track ($\ge $ 3 $\mu $m), they continued to lengthen primarily via end-to-end joining with some reaching lengths greater than 100 $\mu $m. These observations helped define more efficient annealing protocols that resulted in tubes with fewer imperfections.   

Laser Assisted Cancer Immunotherapy: Mapping of the Necrosis Zone

The primary goal of this project is to assess the degree of thermal damage in malignant tumors using Laser Assisted Cancer Immunotherapy (LACI). In our laboratory, superficial tumors were grown in Balb/c mice by injection (s.c.) of the highly aggressive metastatic mammary cell line CRL-2539. When the tumors reached 5-7 mm in diameter, Indocyanine Green, a light absorbing dye, and Glycated Chitosan, the immunoadjuvant, were injected into the tumors. Following injection, the tumors were irradiated interstitially with an infrared Diode laser (1-15 W) operating at 805nm. Following the laser therapy, at a particular temperature, the tumors were excised at various time intervals ranging from immediately after treatment to 120 hours later. Using a Hematoxylin and Eosin stain, each slide was examined under the light microscope to map out the thermal damage induced by the diode laser and the dye-immunoadjuvant combination. The goal of this experiment is to quantify and map the thermal damage for 55$^{o}$C, 65$^{o}$C and 75$^{o}$C, and to determine the temperature range that evokes maximum immune response.   

Interstitial Laser Irradiation of Solid Tumors in Laser Assisted Cancer Immunotherapy

Laser Assisted Cancer Immunotherapy (LACI) is an experimental therapeutic approach in cancer treatment. Current experiments in our laboratory begin with growing superficial tumors 5 to 7 mm in diameter in BALB/C mice using the CRL-2539 cell line. Tumor sizes were measured with a vernier caliper prior to injection of light absorbing dye (Indocyanine Green, ICG) and immunoadjuvant (Glycated Chitosan, GC). These measurements were continued during the post-therapy period. After injection with the ICG and GC, the mice underwent interstitial irradiation of the tumor with a diode laser operating at 804 nm. Microthermocouples were inserted into the tumor and the laser power was varied in order to monitor the temperature and keep it within in the desired range. Tumors were irradiated at 55$^{o} $C, 65$^{o}$C, and 75$^{o}$C to find out at which temperature the maximum amount of tumor necrosis and strong immune response could be elicited. The growth of the tumors after the LACI treatment will be plotted to show the affect of the therapy at different temperatures. The data suggest that the growth rate of the tumors is slowed down considerably using this approach. * This work is supported by a grant from The National Institutes of Health.   

Laser Assisted Cancer Immunotherapy: Surface Irradiation

Experiments in our laboratory incorporate a non-invasive approach to treat superficial tumors in animal models. Based on the concept of Laser Assisted Cancer Immunotherapy, surface irradiation provides good information to compare to invasive alternatives. The procedure involves injecting an immunoadjuvant (Glycated Chitosan) as well as a light absorbing dye (Indocyanine Green) directly into the tumor (5 to 7 mm in diameter). The temperature of the tumor is raised using an infrared diode laser operating at 804 nm, with a silica fiber tip placed a set distance away from the surface of the tumor. We monitor the surface temperature using non-invasive (infrared detector probe) as well as the internal temperature of the tumor using invasive (micro thermocouples) methods. This study aims at the success of the surface irradiation mode to treat solid tumors. * This work is supported by a grant from The National Institute of Health.   

The Computer Generation of Holographic Optical Tweezers

Due to their ability to apply forces on a small scale, optical tweezers are useful for a variety of biological and physical applications. The utility of optical tweezers can be extended by producing multiple traps with different characteristics from a single beam. One method for achieving this is to manipulate the phase of a trapping laser's wave front with a computer generated kinoform displayed on a spatial light modulator. We compare the performance of two algorithms for kinoform calculation, a Gerchberg-Saxton algorithm and a direct search algorithm, and discuss how they address problems inherent to computer generated holographic optical tweezing.   

Growth and Evaporation of Optically Trapped Liquid Droplets Viewed with a Two Axis Microscope

Water droplets in air can be trapped in a single-beam optical trap (optical tweezers) for extended periods of time. The trap used in this work is a unique two axis microscope system that allows the trapped object to be viewed from the top and the side simultaneously. Both views are imaged onto a single digital camera with temporal resolution of better than 5ms. We will report on the behavior of water droplets as they grow and evaporate while in the trap. We will discuss changes in the size and shape of the droplets over time, the onset of instabilities during the evaporation process, and how the trapping laser power affects the droplet. This research was supported by an award from Research Corporation.   

Leidenfrost Ratchets

Properties such as asymmetry and disequilibrium can be exploited in order to obtain useful work from a physical system. Our group is investigating one particularly interesting manifestation of the ``ratchet'' effect. We find that film-boiling (leidenfrost) drops of liquid placed on an asymmetrically-structured surface experience acceleration significant enough for transport to occur even against small inclines. We believe that a viscous drag force is the mechanism for this net flow of fluid, which is supported by a thin layer of vapor. Because heat is the primary input of energy into the system, this effect could prove useful in cooling applications where a classical ``pump'' may not be ideal.   

The effect of M ( M=Ti, V) and A (A=Al, Ge) on thermal transport and heat capacity of nanolayered ternary carbides M$_{2}$AC

We report an investigation of the specific heat and the thermal transport of a subset of the so-called MAX-phase family of materials: V$_{2}$GeC, V$_{2}$AlC, Ti$_{2}$GeC and Ti$_{2}$AlC. The thermal transport results are analyzed to investigate the impact of the A-group and M-element on the phonon contribution to the thermal transport. The heat capacity results are investigated to determine the impact of the same elements on the density of electronic states and the Debye temperature. We find that M-element has a more significant impact on the electronic density of states and the thermopower. The Seebeck coefficient is significantly larger in the V-containing carbides (it is nearly zero in the Ti$_{2}$AC compounds), although the sign is dependent on the A-group element. The A-group element has an expected impact on the Debye temperature due to the change in atomic masses, but the phonon contribution to the thermal conductivity is largest in the V$_{2}$AC compounds   

Electron Spin Resonance of VO$_{2}$ thin films

The metal-insulator transition present in chromium doped VO$_{2}$ nanoscale film has been observed by electron spin resonance (ESR) spectroscopy. VO$_{2}$ is a highly correlated electron system with numerous practical applications pertaining to this transition, including ultra-fast optical switching and smart windows. We use Cr$^{3+}$ transition metal ions with concentration of order one percent as a probe in a 140 nm film to detect this transition. The film exhibited a four-fold decrease in chromium intensity as temperature increased through the transition temperature ($\sim $67$^{\circ}$ C). ESR signal intensities were also used to characterize the hysteretic behavior of this particular transition; these results are in agreement with hysteresis observed through optical means. A discussion of how changes in ESR relaxation times affect signal intensities, as monitored through the transition, will be presented.   

EPR Study of Amorphous V$_{2}$O$_{5 }$From 125K -- 370K

Previous EPR spectra for V$_{2}$O$_{5}$ at low temperatures ($\sim $120K) reveal well-resolved resonances in which transitions are attributed to anisotropic hyperfine interactions. In contrast, recent results from our laboratory show EPR spectra with broad resonances that exist from 125K-370K with no apparent appearance of hyperfine interactions. EPR spin counting also indicates a high concentration ($\sim $10$^{20}$ spins/cm$^{3})$ of paramagnetic centers which suggests that the line widths are limited by spin-spin relaxation of the electron spin system. Current data reveal that EPR signal intensities increase more rapidly than (Temperature)$^{-1}$. In particular, a factor of $\sim $10 increase is seen when the temperature is decreased by a factor of 2. Possibilities for enhanced signal intensities include the presence of superparamagnetism or spin glass behavior. Current investigations are concerned with evaluations of a variety of EPR parameters over a temperature range from 125-370K.   

Mean-Field Study of Magnetic Resonance for Spin-1 Condensates

A spin-1 alkali atom has three hyperfine spin levels $\vert $f=1,m=-1,0,+1$>$. An optical dipole trap is capable of simultaneously trapping and condensing all the hyperfine states, forming the so-called spinor Bose-Einstein condensate (BEC), where the spin degrees of freedom are virtually free. The spin-1 BEC is amenable to manipulation by magnetic field. Magnetic resonance theory is developed for a spin-1 BEC subject to both a rotating transverse magnetic field and a longitudinal magnetic field. The focus of the theory is the magnetization, which will be analyzed both analytically and numerically. Magnetization is used to probe the nonlinear two-body collisions, which strongly affect the properties of the spin-1 BEC. It is shown that while collisions modulate the population dynamics, it is the quadratic Zeeman interaction that couples the population dynamics due to collisions to the magnetization.   

Width of a Ferrofluid Finger: Hysteresis and Multiple Energy Minima

The theoretical finger width dependence of a ferrofluid on the magnetic field in a Hele-Shaw geometry is investigated. A model of the finger enables the energy to be computed and then minimized to determine the finger width. Calculations predict a hysteresis effect as the applied magnetic field is varied. This results from the existence of two local energy minima for a range of magnetic bond numbers. Hence, for a given magnetic bond number, the stable ferrofluid configuration can be either a circle or a finger, depending on the whether the applied field is increasing or decreasing. A comparison with experimental results will be presented.   

Design of Low Temperature AC Susceptibility Measurement Scheme for Molecular Magnets

AC susceptibility is one of the most important physical properties in many materials such as magnetic materials and superconductors. Although there are many commercial AC susceptibility measurement systems which cover a broad range of temperatures, it is still a daunting task to extend their measurement range into the low millikelvins. We are currently developing a low temperature AC susceptometer for the mK range. As a part of this effort, we have developed a versatile low-cost computer controlled coil-winder to make various types of coils. We have designed primary and secondary coils and wound them using the machine, and performed characterization of the AC susceptometer. In this presentation, I will explain the basics of magnetic susceptibility, its measurement, design considerations for building an AC magnetic susceptometer, and discuss the details of an actual apparatus designed and realized by the authors.