Single grain heating due to inelastic cotunneling

We study heating effects of a single metallic quantum dot weakly coupled to two leads. The dominant mechanism for heating at low temperatures is due to inelastic electron cotunneling processes. We calculate the grain temperature profile as a function of grain parameters, bias voltage, and time and show that for nanoscale size grains the heating effects are pronounced and easily measurable in experiments.Comment: 4 pages, 3 figures, revtex4, extended and corrected versio

Studies of inactivation mechanism of non-enveloped icosahedral virus by a visible ultrashort pulsed laser

BACKGROUND: Low-power ultrashort pulsed (USP) lasers operating at wavelengths of 425 nm and near infrared region have been shown to effectively inactivate viruses such as human immunodeficiency virus (HIV), M13 bacteriophage, and murine cytomegalovirus (MCMV). It was shown previously that non-enveloped, helical viruses such as M13 bacteriophage, were inactivated by a USP laser through an impulsive stimulated Raman scattering (ISRS) process. Recently, enveloped virus like MCMV has been shown to be inactivated by a USP laser via protein aggregation induced by an ISRS process. However, the inactivation mechanism for a clinically important class of viruses – non-enveloped, icosahedral viruses remains unknown. RESULTS AND DISCUSSIONS: We have ruled out the following four possible inactivation mechanisms for non-enveloped, icosahedral viruses, namely, (1) inactivation due to ultraviolet C (UVC) photons produced by non-linear optical process of the intense, fundamental laser beam at 425 nm; (2) inactivation caused by thermal heating generated by the direct laser absorption/heating of the virion; (3) inactivation resulting from a one-photon absorption process via chromophores such as porphyrin molecules, or indicator dyes, potentially producing reactive oxygen or other species; (4) inactivation by the USP lasers in which the extremely intense laser pulse produces shock wave-like vibrations upon impact with the viral particle. We present data which support that the inactivation mechanism for non-enveloped, icosahedral viruses is the impulsive stimulated Raman scattering process. Real-time PCR experiments show that, within the amplicon size of 273 bp tested, there is no damage on the genome of MNV-1 caused by the USP laser irradiation. CONCLUSION: We conclude that our model non-enveloped virus, MNV-1, is inactivated by the ISRS process. These studies provide fundamental knowledge on photon-virus interactions on femtosecond time scales. From the analysis of the transmission electron microscope (TEM) images of viral particles before and after USP laser irradiation, the locations of weak structural links on the capsid of MNV-1 were revealed. This important information will greatly aid our understanding of the structure of non-enveloped, icosahedral viruses. We envision that this non-invasive, efficient viral eradication method will find applications in the disinfection of pharmaceuticals, biologicals and blood products in the near future

Chemical-free inactivated whole influenza virus vaccine prepared by ultrashort pulsed laser treatment

There is an urgent need for rapid methods to develop vaccines in response to emerging viral pathogens. Whole inactivated virus (WIV) vaccines represent an ideal strategy for this purpose; however, a universal method for producing safe and immunogenic inactivated vaccines is lacking. Conventional pathogen inactivation methods such as formalin, heat, ultraviolet light, and gamma rays cause structural alterations in vaccines that lead to reduced neutralizing antibody specificity, and in some cases, disastrous T helper type 2-mediated immune pathology. We have evaluated the potential of a visible ultrashort pulsed (USP) laser method to generate safe and immunogenic WIV vaccines without adjuvants. Specifically, we demonstrate that vaccination of mice with laser-inactivated H1N1 influenza virus at about a 10-fold lower dose than that required using conventional formalin-inactivated influenza vaccines results in protection against lethal H1N1 challenge in mice. The virus, inactivated by the USP laser irradiation, has been shown to retain its surface protein structure through hemagglutination assay. Unlike conventional inactivation methods, laser treatment did not generate carbonyl groups in protein, thereby reducing the risk of adverse vaccine-elicited T helper type 2 responses. Therefore, USP laser treatment is an attractive potential strategy to generate WIV vaccines with greater potency and safety than vaccines produced by current inactivation techniques

Pathogen reduction in human plasma using an ultrashort pulsed laser

Pathogen reduction is a viable approach to ensure the continued safety of the blood supply against emerging pathogens. However, the currently licensed pathogen reduction techniques are ineffective against non-enveloped viruses such as hepatitis A virus, and they introduce chemicals with concerns of side effects which prevent their widespread use. In this report, we demonstrate the inactivation of both enveloped and non-enveloped viruses in human plasma using a novel chemical-free method, a visible ultrashort pulsed laser. We found that laser treatment resulted in 2-log, 1-log, and 3-log reductions in human immunodeficiency virus, hepatitis A virus, and murine cytomegalovirus in human plasma, respectively. Laser-treated plasma showed ≥70% retention for most coagulation factors tested. Furthermore, laser treatment did not alter the structure of a model coagulation factor, fibrinogen. Ultrashort pulsed lasers are a promising new method for chemical-free, broad-spectrum pathogen reduction in human plasma

LASER EXCITED POPULATIONS OF ELECTRONS AND PHONONS IN GALLIUM-ARSENIDE: RAMAN SCATTERING PROBE STUDIES

This research work has involved the use of Raman scattering as a probe of the solid state plasma and of the phonons in GaAs. A high power YA1G laser capable of operating in Cw and Q-switched modes was employed to investigate both the equilibrium and non-equilibrium distributions of electrons as well as of phonons. The same laser, in the Q-switched mode, was used for changing the electron and phonon distributions and, in situ, for probing those changes by Raman scattering. We have demonstrated that Raman scattering can serve as a good, universal probe for non-equilibrium electron distributions and for excess phonons throughout the Brillouin zone. The work which has been accomplished can be divided into two categories: (1) For the low-laser-intensity, equilibrium case, theoretical analysis of the single particle scattering line shape associated with the charge density, spin density and energy density fluctuation mechanisms have been carried out and were compared with our experimental data. We studied the effects of band structure, carried concentration and collisions on each of these mechanisms. From the combined theoretical and experimental analysis, we found that one had to be very cautious in using single particle scattering as a probe of non-equilibrium electron distribution function. The spin density fluctuation mechanisms was shown to be best suited for this purpose, but not without significant corrections, e.g., for band structure effect and collisions. (2) For the high-laser-intensity, non-equilibrium case, at laser intensity of (TURN) 3 MW/cm(\u272), we were able to excite (TURN) 5 x 10(\u2715)/cm(\u273) electrons from deep traps in GaAs at low temperature ((TURN) 25 K). The non-equilibrium phonons generated through non-radiative recombination of these electrons onto the traps and non-equilibrium electron distribution were reflected in the Raman scattering spectrum. The feasibility and general utility of using two-phonon Raman scattering for probing non-equilibrium large wave vector TA (transverse acoustic) phonons was demonstrated. We obtained important new information about the TA phonon bottleneck in GaAs at low temperature recently observed by heat pulse measurements (Ulbrich, Narayanamurti, et al.). Our work provided verification of the existence of the bottleneck and the first specification of the frequencies and populations of the non-equilibrium phonons throughout the Brillouin zone. We discovered that the phonon enhancement was not restricted to the lowest, softest TA branch, but occurred also for the fast TA phonons

Prospects for a novel ultrashort pulsed laser technology for pathogen inactivation

<p>Abstract</p> <p>The threat of emerging pathogens and microbial drug resistance has spurred tremendous efforts to develop new and more effective antimicrobial strategies. Recently, a novel ultrashort pulsed (USP) laser technology has been developed that enables efficient and chemical-free inactivation of a wide spectrum of viral and bacterial pathogens. Such a technology circumvents the need to introduce potentially toxic chemicals and could permit safe and environmentally friendly pathogen reduction, with a multitude of possible applications including the sterilization of pharmaceuticals and blood products, and the generation of attenuated or inactivated vaccines.</p