Comparison of the INRIM and PTB lattice-spacing standards

To base the kilogram definition on the atomic mass of the silicon 28 atom, the present relative uncertainty of the silicon 28 lattice parameter must lowered to 3E-9. To achieve this goal, a new experimental apparatus capable of a centimetre measurement-baseline has been made at the INRIM. The comparison between the determinations of the lattice parameter of crystals MO*4 of INRIM and WASO4.2a of PTB is intended to verify the measurement capabilities and to assess the limits of this experiment.Comment: 10 pages, 8 figures, submitted to Metrologi

A Conversation with Leo Goodman

Leo A. Goodman was born on August 7, 1928 in New York City. He received his A.B. degree, summa cum laude, in 1948 from Syracuse University, majoring in mathematics and sociology. He went on to pursue graduate studies in mathematics, with an emphasis on mathematical statistics, in the Mathematics Department at Princeton University, and in 1950 he was awarded the M.A. and Ph.D. degrees. His statistics professors at Princeton were the late Sam Wilks and John Tukey. Goodman then began his academic career as a statistician, and also as a statistician bridging sociology and statistics, with an appointment in 1950 as assistant professor in the Statistics Department and the Sociology Department at the University of Chicago, where he remained, except for various leaves, until 1987. He was promoted to associate professor in 1953, and to professor in 1955. Goodman was at Cambridge University in 1953--1954 and 1959--1960 as visiting professor at Clare College and in the Statistical Laboratory. And he spent 1960--1961 as a visiting professor of mathematical statistics and sociology at Columbia University. He was also a research associate in the University of Chicago Population Research Center from 1967 to 1987. In 1970 he was appointed the Charles L. Hutchinson Distinguished Service Professor at the University of Chicago, a title that he held until 1987. He spent 1984--1985 at the Center for Advanced Study in the Behavioral Sciences in Stanford. In 1987 he was appointed the Class of 1938 Professor at the University of California, Berkeley, in the Sociology Department and the Statistics Department. Goodman's numerous honors include honorary D.Sc. degrees from the University of Michigan and Syracuse University, and membership in the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society.Comment: Published in at http://dx.doi.org/10.1214/08-STS276 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

HST Proper Motion confirms the optical identification of the nearby pulsar PSR 1929+10

We report on the proper motion measurement of the proposed optical counterpart of the X-ray/radio pulsar PSR 1929+10. Using images obtained with the HST/STIS (average epoch 2001.73) we computed a yearly displacement of +97 +/- 1 mas yr^{-1} in RA and +46 +/- 1 mas yr^{-1} in Dec since the epoch (1994.52) of the original HST/FOC detection. Both the magnitude and direction of the optical proper motion components are found to be fully consistent with the most recent VLBA radio measurements. This result provides an unambiguous confirmation of the pulsar optical identification. In addition, we have used the combined STIS/FOC datasets to derive information on the pulsar spectrum, which seems characterized by a power law component, apparently unrelated to the X-ray emission.Comment: 12 pages, 3 figures, submitted to ApJ Letter

Pointless Hyperelliptic Curves

In this paper we consider the question of whether there exists a hyperelliptic curve of genus g which is defined over but has no rational points over for various pairs . As an example of such a result, we show that if p is a prime such that is also prime then there will be pointless hyperelliptic curves over of every genus

Atmospheric Heat Redistribution on Hot Jupiters

Infrared lightcurves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy absorbed on their daysides---and thus have a larger day-night temperature contrast---than colder planets. No predictive atmospheric model has been published that identifies which dynamical mechanisms determine the atmospheric heat redistribution efficiency on tidally locked exoplanets. Here we present a two-layer shallow water model of the atmospheric dynamics on synchronously rotating planets that explains the observed trend. Our model shows that planets with weak friction and weak irradiation exhibit a banded zonal flow with minimal day-night temperature differences, while models with strong irradiation and/or strong friction exhibit a day-night flow pattern with order-unity fractional day-night temperature differences. To interpret the model, we develop a scaling theory that shows that the timescale for gravity waves to propagate horizontally over planetary scales, t_wave, plays a dominant role in controlling the transition from small to large temperature contrasts. This implies that heat redistribution is governed by a wave-like process, similar to the one responsible for the weak temperature gradients in the Earth's tropics. When atmospheric drag can be neglected, the transition from small to large day-night temperature contrasts occurs when t_wave ~ sqrt(t_rad/Omega), where t_rad is the radiative relaxation time and Omega is the planetary rotation frequency. Alternatively, this transition criterion can be expressed as t_rad ~ t_vert, where t_vert is the timescale for a fluid parcel to move vertically over the difference in day-night thickness. These results subsume the commonly used timescale comparison for estimating heat redistribution efficiency between t_rad and the global horizontal advection timescale, t_adv.Comment: Accepted to ApJ with minor edits compared to version 1; 17 pages, 11 figure

Cyclic Critical Groups of Graphs

In this note, we describe a construction that leads to families of graphs whose critical groups are cyclic. For some of these families we are able to give a formula for the number of spanning trees of the graph, which then determines the group exactly

The Deep Lens Survey Transient Search I : Short Timescale and Astrometric Variability

We report on the methodology and first results from the Deep Lens Survey transient search. We utilize image subtraction on survey data to yield all sources of optical variability down to 24th magnitude. Images are analyzed immediately after acquisition, at the telescope and in near-real time, to allow for followup in the case of time-critical events. All classes of transients are posted to the web upon detection. Our observing strategy allows sensitivity to variability over several decades in timescale. The DLS is the first survey to classify and report all types of photometric and astrometric variability detected, including solar system objects, variable stars, supernovae, and short timescale phenomena. Three unusual optical transient events were detected, flaring on thousand-second timescales. All three events were seen in the B passband, suggesting blue color indices for the phenomena. One event (OT 20020115) is determined to be from a flaring Galactic dwarf star of spectral type dM4. From the remaining two events, we find an overall rate of \eta = 1.4 events deg-2 day-1 on thousand-second timescales, with a 95% confidence limit of \eta < 4.3. One of these events (OT 20010326) originated from a compact precursor in the field of galaxy cluster Abell 1836, and its nature is uncertain. For the second (OT 20030305) we find strong evidence for an extended extragalactic host. A dearth of such events in the R passband yields an upper 95% confidence limit on short timescale astronomical variability between 19.5 < R < 23.4 of \eta_R < 5.2. We report also on our ensemble of astrometrically variable objects, as well as an example of photometric variability with an undetected precursor.Comment: 24 pages, 12 figures, 3 tables. Accepted for publication in ApJ. Variability data available at http://dls.bell-labs.com/transients.htm