Reaction Time of a Group of Physics Students

The reaction time of a group of students majoring in Physics is reported here. Strong co-relation between fatigue, reaction time and performance have been seen and may be useful for academicians and administrators responsible of working out time-tables, course structures, students counsellings etc.Comment: 10 pages, 4 figure

On ordinal utility, cardinal utility, and random utility

Though the Random Utility Model (RUM) was conceived  entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties of  cardinal utility.  The adoption of cardinal utility as a  working operation of ordinal is perfectly valid, provided  interpretations drawn from that operation remain faithful  to ordinal utility.  The paper considers whether the latterrequirement holds true for several measurements commonly  derived from RUM.  In particular it is found that  measurements of consumer surplus change may depart from  ordinal utility, and exploit the cardinality inherent in  the practical apparatus.

Response theory for time-resolved second-harmonic generation and two-photon photoemission

A unified response theory for the time-resolved nonlinear light generation and two-photon photoemission (2PPE) from metal surfaces is presented. The theory allows to describe the dependence of the nonlinear optical response and the photoelectron yield, respectively, on the time dependence of the exciting light field. Quantum-mechanical interference effects affect the results significantly. Contributions to 2PPE due to the optical nonlinearity of the surface region are derived and shown to be relevant close to a plasmon resonance. The interplay between pulse shape, relaxation times of excited electrons, and band structure is analyzed directly in the time domain. While our theory works for arbitrary pulse shapes, we mainly focus on the case of two pulses of the same mean frequency. Difficulties in extracting relaxation rates from pump-probe experiments are discussed, for example due to the effect of detuning of intermediate states on the interference. The theory also allows to determine the range of validity of the optical Bloch equations and of semiclassical rate equations, respectively. Finally, we discuss how collective plasma excitations affect the nonlinear optical response and 2PPE.Comment: 27 pages, including 11 figures, version as publishe

Current profile modification with electron cyclotron current drive in the DIII-D tokamak

Proof-of-principle experiments on the suitability of electron cyclotron current drive (ECCD) for active current profile control are reported. Experiments with second harmonic extraordinary mode absorption at power levels near 1 MW have demonstrated ability to modify the current profile. This modification is manifested in changes in the internal inductance and the time at which sawteeth appear. Measurements of the local current density and internal loop voltage using high resolution motional Stark effect spectroscopy to half of the minor radius in discharges with localized deposition clearly demonstrate localized off-axis ECCD at the predicted location. Comparison with theory indicates the detrimental effect of trapped electrons on the current drive efficiency is less than predicted. Modification of the theory for finite collisionality is the leading candidate to explain the observations

The UN in the lab

We consider two alternatives to inaction for governments combating terrorism, which we term Defense and Prevention. Defense consists of investing in resources that reduce the impact of an attack, and generates a negative externality to other governments, making their countries a more attractive objective for terrorists. In contrast, Prevention, which consists of investing in resources that reduce the ability of the terrorist organization to mount an attack, creates a positive externality by reducing the overall threat of terrorism for all. This interaction is captured using a simple 3×3 “Nested Prisoner’s Dilemma” game, with a single Nash equilibrium where both countries choose Defense. Due to the structure of this interaction, countries can benefit from coordination of policy choices, and international institutions (such as the UN) can be utilized to facilitate coordination by implementing agreements to share the burden of Prevention. We introduce an institution that implements a burden-sharing policy for Prevention, and investigate experimentally whether subjects coordinate on a cooperative strategy more frequently under different levels of cost sharing. In all treatments, burden sharing leaves the Prisoner’s Dilemma structure and Nash equilibrium of the game unchanged. We compare three levels of burden sharing to a baseline in a between-subjects design, and find that burden sharing generates a non-linear effect on the choice of the efficient Prevention strategy and overall performance. Only an institution supporting a high level of mandatory burden sharing generates a significant improvement in the use of the Prevention strategy

Implications from dimensionless parameter scaling experiments

The dimensionless parameter scaling approach is increasingly useful for predicting future tokamak performance and guiding theoretical models of energy transport. Experiments to determine the {rho}* (gyroradius normalized to plasma size) scaling have been carried out in many regimes. The electron {rho}* scaling is always ``gyro-Bohm``, while the ion {rho}* scaling varied with regime. The ion variation is correlated with both density scale length (L mode, H mode) and current profile. The ion {rho}* scaling in the low-q, H-mode regime is gyro-Bohm, which is the most favorable confinement scaling observed. New experiments in {beta} scaling and collisionality scaling have been carried out in low-q discharges in both L mode and H mode. In L mode, global analysis shows that there is a slightly unfavorable {beta} dependence ({beta}{sup {minus}0.1}) and no {nu}* dependence. In H-mode, global analysis finds a weak {beta} dependence ({beta}{sup 0.1}) and an unfavorable dependence on {nu}*. The lack of significant {beta} scaling spans the range of {beta}{sub N} from 0.25 to 2.0. The very small {beta} dependence in L mode and H mode is in contradiction with the standard global scaling relations. This contradiction in H mode may be indicative of the impact on the H-mode database of low-n tearing instabilities which are observed at slightly higher {beta}{sub N} in the {beta} scaling experiments. The measured {beta} and {nu}* scalings explain the weak density dependence observed in engineering parameter scans. It also points to the power of the dimensionless parameter approach, since it is possible to obtain a definitive size scaling from experiments on a single tokamak