Lighter than air: A look at the past, a look at the possibilities

A brief history of the flight by LTA including the development of the zeppelin is presented. Safety and economy are discussed along with power requirements and production techniques. The problem of ground handling facilities for very large airships are briefly mentioned

Man's exploration of space

Apollo spacecraft developmen

An update on the correlation between the cosmic radiation intensity and the geomagnetic AA index

A statistical study between the cosmic ray intensity, as observed by a neutron monitor, and of the geomagnetic aa index, as representative of perturbations in the plasma and interplanetary magnetic field in the heliosphere, has been updated to specifically exclude time periods around the reversal of the solar magnetic field. The results of this study show a strong negative correlation for the period 1960 through 1968 with a correlation coefficient of approximately -0.86. However, there is essentially no correlation between the cosmic ray intensity and the aa index for the period 1972-1979 (i.e. correlation coefficient less than 0.16). These results would appear to support the theory of preferential particle propagation into the heliosphere vis the ecliptic during the period 1960-1968 and via the solar polar regions during 1972-1979

The Power of Suggestion: Inertia in 401(k) Participation and Savings Behavior

In this paper, we analyze the 401(k) savings behavior of employees in a large U.S. corporation before and after an interesting change in the company 401(k) plan. Before the plan change, employees were required to affirmatively elect participation in the 401(k) plan. After the plan change, employees were automatically and immediately enrolled in the 401(k) plan unless they made a negative election to opt out of the plan. Although none of the economic features of the plan changed, this switch to automatic enrollment dramatically changed the savings behavior of employees. We have two key findings. First, 401(k) participation is significantly higher under automatic enrollment. Second, the default contribution rate and investment allocation chosen by the company under automatic enrollment has a strong influence on the savings behavior of 401(k) participants. A substantial fraction of 401(k) participants hired under automatic enrollment exhibit what we call default' behavior--sticking to both the default contribution rate and the default fund allocation even though very few employees hired before automatic enrollment picked this particular outcome. This default' behavior appears to result both from participant inertia and from many employees taking the default as investment advice on the part of the company. Overall, these results are consistent with the notion that large changes in savings behavior can be motivated simply by the power of suggestion.' These findings have important implications for the optimal design of 401(k) savings plans as well as for any type of Social Security reform that includes personal accounts over which individuals have some amount of control. They also shed light more generally on the importance of both economic and non-economic factors in the determination of individual savings behavior.

LDPC Code Design for the BPSK-constrained Gaussian Wiretap Channel

A coding scheme based on irregular low-density parity-check (LDPC) codes is proposed to send secret messages from a source over the Gaussian wiretap channel to a destination in the presence of a wiretapper, with the restriction that the source can send only binary phase-shift keyed (BPSK) symbols. The secrecy performance of the proposed coding scheme is measured by the secret message rate through the wiretap channel as well as the equivocation rate about the message at the wiretapper. A code search procedure is suggested to obtain irregular LDPC codes that achieve good secrecy performance in such context.Comment: submitted to IEEE GLOBECOM 2011 - Communication Theory Symposiu