Deriving star formation histories: Inverting HR diagrams through a variational calculus maximum likelihood method

We introduce a new method for solving maximum likelihood problems through variational calculus, and apply it to the case of recovering an unknown star formation history, $SFR(t)$, from a resulting HR diagram. This approach allows a totally non-parametric solution which has the advantage of requiring no initial assumptions on the $SFR(t)$. As a full maximum likelihood statistical model is used, we take advantage of all the information available in the HR diagram, rather than concentrating on particular features such as turn off points or luminosity functions. We test the method using a series of synthetic HR diagrams produced from known $SFR(t)$, and find it to be quite successful under noise conditions comparable to those present in current observations. At this point we restrict the analysis to situations where the metallicity of the system is known, as is the case with the resolved populations of the dwarf spheroidal companions to the Milky Way or the solar neighbourhood Hipparcos data. We also include tests to quantify the way uncertainties in the assumed metallicity, binary fraction and IMF affect our inferences.Comment: 16 pages including 12 figures. Accepted for publication in MNRAS, appendix adde

Spatial effects upon employment outcomes: the case of New Jersey teenagers

Employment (Economic theory) ; Econometric models ; Income distribution ; New Jersey

Baseband Radio over Fiber Aided Millimeter-Wave Distributed Antenna for Optical/Wireless Integration

A Baseband Radio Over Fiber (BROF) architecture is proposed, where upto four Radio Frequency (RF) carriers can be generated, while using the heterodyne photo-detection of only two optical signals. This proposed BROF architecture has a star-like structure and it is composed of six Radio Access Units (RAUs), where data is transmitted from the Central Unit (CU) to the Base Station (BS) and from the BS to the RAU over a distance of 20 Km and 0.3 Km, respectively, at a rate of 768 Mbps. The performance of the system supporting four carrier frequencies drops by at most 1dB, at a BER of 10-9, compared to conventional heterodyne photo-detection

Outage Probability of Multiple-Input Single-Output (MISO) Systems with Delayed Feedback

We investigate the effect of feedback delay on the outage probability of multiple-input single-output (MISO) fading channels. Channel state information at the transmitter (CSIT) is a delayed version of the channel state information available at the receiver (CSIR). We consider two cases of CSIR: (a) perfect CSIR and (b) CSI estimated at the receiver using training symbols. With perfect CSIR, under a short-term power constraint, we determine: (a) the outage probability for beamforming with imperfect CSIT (BF-IC) analytically, and (b) the optimal spatial power allocation (OSPA) scheme that minimizes outage numerically. Results show that, for delayed CSIT, BF-IC is close to optimal for low SNR and uniform spatial power allocation (USPA) is close to optimal at high SNR. Similarly, under a long-term power constraint, we show that BF-IC is close to optimal for low SNR and USPA is close to optimal at high SNR. With imperfect CSIR, we obtain an upper bound on the outage probability with USPA and BF-IC. Results show that the loss in performance due to imperfection in CSIR is not significant, if the training power is chosen appropriately.Comment: Submitted to IEEE Transactions on Communications Jan 2007, Revised Jun 2007, Revised Nov 200

College Preparation for African American Students: Gaps in the High School Educational Experience

This report focuses on the deficiencies and disparities in school systems, particularly those with high-minority populations, that leave students unprepared for the rigors of college. It addresses three key areas that are critical for college readiness: the level of coursework available, the experience level of the teachers, and access to guidance counselors., and provides implications for public policy

Reasons stated by commencing students for studying engineering and technology

Responses were collected from commencing engineering students and an inventory of reasons stated for electing to study engineering was developed. Commencing engineering students were strongly career oriented; they believed that engineering would be an interesting and rewarding career that would offer enjoyment and career options. No difference was found in the principal reasons stated by respondents based on gender or course of study. On-campus students nominated principally career-related reasons for their choice of study (71 percent). While career-related reasons were still important for off-campus students, the most frequent type of responses were related to career upgrading (43.9 percent).<br /

The security implications of geoengineering:blame,imposed agreement and the security of critical infrastructure

The prospect of solar geoengineering in response to climate change (on the basis of its supposedly significantly lower cost and/or more rapid impact on global temperature than carbon reduction strategies) raises a number of security concerns that have traditionally been understood within a standard Geo-political framing of security. This relates to unrealistic direct application in inter-State warfare or to a securitization of climate change. However, indirect security implications are potentially significant. Current capability, security threats and international law loopholes suggest the military, rather than scientists would undertake geoengineering, and solar radiation management (SRM) in particular. SRM activity would be covered by Critical National Infrastructure policies, and as such would require a significant level of secondary security infrastructure. Concerns about termination effects, the need to impose international policy agreement 4 (given the ability of 'rogue States' to disrupt SRM and existing difficulties in producing global agreement on climate policy), and a world of extreme weather events, where weather is engineered and hence blameworthy rather than natural, suggest these costs would be large. Evidence on how blame is attributed suggest blame for extreme weather events may be directed towards more technologically advanced nations, (such as the USA) even if they are not engaged in geoengineering. From a security perspective SRM is costly, ungovernable, and raises security concerns of a sufficient magnitude to make it a non-viable policy option