Does a Simple Lattice Protein Exhibit Self-Organized Criticality?

There are many unanswered questions when it comes to protein folding. These questions are interesting because the tertiary structure of proteins determines its functionality in living organisms. How do proteins consistently reach their final tertiary structure from the primary sequence of amino acids? What explains the complexity of tertiary structures? Our research uses a simple hydrophobic-polar lattice-bound computational model to investigate self-organized criticality as a possible mechanism for generating complexity in protein folding and protein tertiary structures

Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma

It is shown, by simulation and theory, that circularly or elliptically polarized terahertz radiation can be generated when a static magnetic (B) field is imposed on a gas target along the propagation direction of a two-color laser driver. The radiation frequency is determined by $\sqrt{\omega_p^2+{\omega_c^2}/{4}} + {\omega_c}/{2}$, where $\omega_p$ is the plasma frequency and $\omega_c$ is the electron cyclotron frequency. With the increase of the B field, the radiation changes from a single-cycle broadband waveform to a continuous narrow-band emission. In high-B-field cases, the radiation strength is proportional to $\omega_p^2/\omega_c$. The B field provides a tunability in the radiation frequency, spectrum width, and field strength.Comment: 6 pages, 5 figure

Composite drill stem of epoxy fiber glass reinforced with boron filaments and a retrievable core liner/sample return container for the Apollo lunar surface drill

Composite drill stem of epoxy fiber glass and boron filaments and lunar core sampling system for Apollo lunar surface dril

Laser ion acceleration using a solid target coupled with a low density layer

We investigate by particle-in-cell simulations in two and three dimensions the laser-plasma interaction and the proton acceleration in multilayer targets where a low density "near-critical" layer of a few micron thickness is added on the illuminated side of a thin, high density layer. This target design can be obtained by depositing a "foam" layer on a thin metallic foil. The presence of the near-critical plasma strongly increases both the conversion efficiency and the energy of electrons and leads to enhanced acceleration of proton from a rear side layer via the Target Normal Sheath Acceleration mechanism. The electrons of the foam are strongly accelerated in the forward direction and propagate on the rear side of the target building up a high electric field with a relatively flat longitudinal profile. In these conditions the maximum proton energy is up to three times higher than in the case of the bare solid target.Comment: 9 pages, 11 figures. Submitted to Physical Review

Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects

We investigate how next-generation laser pulses at 10 PW $-$ 200 PW interact with a solid target in the presence of a relativistically underdense preplasma produced by amplified spontaneous emission (ASE). Laser hole boring and relativistic transparency are strongly restrained due to the generation of electron-positron pairs and $\gamma$-ray photons via quantum electrodynamics (QED) processes. A pair plasma with a density above the initial preplasma density is formed, counteracting the electron-free channel produced by the hole boring. This pair-dominated plasma can block the laser transport and trigger an avalanche-like QED cascade, efficiently transfering the laser energy to photons. This renders a 1-$\rm\mu m$-scalelength, underdense preplasma completely opaque to laser pulses at this power level. The QED-induced opacity therefore sets much higher contrast requirements for such pulse in solid-target experiments than expected by classical plasma physics. Our simulations show for example, that proton acceleration from the rear of a solid with a preplasma would be strongly impaired.Comment: 5 figure

Unifying prospective and retrospective interval-time estimation: a fading-gaussian activation-based model of interval-timing

Hass and Hermann (2012) have shown that only variance-based processes will lead to the scalar growth of error that is characteristic of human time judgments. Secondly, a major meta-review of over one hundred studies (Block et al., 2010) reveals a striking interaction between the way in which temporal judgments are queried and cognitive load on participants’ judgments of interval duration. For retrospective time judgments, estimates under high cognitive load are longer than under low cognitive load. For prospective judgments, the reverse pattern holds, with increased cognitive load leading to shorter estimates. We describe GAMIT, a Gaussian spreading-activation model, in which the sampling rate of an activation trace is differentially affected by cognitive load. The model unifies prospective and retrospective time estimation, normally considered separately, by relating them to the same underlying process. The scalar property of time estimation arises naturally from the model dynamics and the model shows the appropriate interaction between mode of query and cognitive load

Lagrangian analysis of alignment dynamics for isentropic compressible magnetohydrodynamics

After a review of the isentropic compressible magnetohydrodynamics (ICMHD) equations, a quaternionic framework for studying the alignment dynamics of a general fluid flow is explained and applied to the ICMHD equations.Comment: 12 pages, 2 figures, submitted to a Focus Issue of New Journal of Physics on "Magnetohydrodynamics and the Dynamo Problem" J-F Pinton, A Pouquet, E Dormy and S Cowley, editor

Dominance of Radiation Pressure in Ion Acceleration with Linearly Polarized Pulses at Intensities of 1021Wcm−210^{21}\textrm{W}\textrm{cm}^{-2}

A novel regime is proposed where, employing linearly polarized laser pulses at intensities $10^{21}\textrm{Wcm}^{-2}$ as two order of magnitude lower than earlier predicted [T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004)], ions are dominantly accelerated from ultrathin foils by the radiation pressure, and have monoenergetic spectra. In the regime, ions accelerated from the hole-boring process quickly catch up with the ions accelerated by target normal sheath acceleration (TNSA), and they then join in a single bunch, undergoing a hybrid Light-Sail/TNSA acceleration. Under an appropriate coupling condition between foil thickness, laser intensity and pulse duration, laser radiation pressure can be dominant in this hybrid acceleration. Two-dimensional PIC simulations show that $1.26\textrm{GeV}$ quasimonoenergetic $\textrm{C}^{6+}$ beams are obtained by linearly polarized laser pulses at intensities of $10^{21}\textrm{Wcm}^{-2}$.Comment: 6 pages, 4 figure