Predicting sonic pulse shapes of underwater spark discharges

Measurements of the acoustic pressure of spark discharges were made at a shallow depth (10 feet) for various voltages, stored energies, inductances and capacitances of the system, and electrode areas. The voltages ranged from 1500 V to 11 KV, and the energy storing capacitances from 8 to 800 ufd. In this range the peak pressure observed was proportional to peak current and the decay constant of the pressure-time curve was essentially the same as the electrical discharge decay constant.Office of Naval Research under Contract Nonr 1 367(00) NR 261-10

Quarantine region scheme to mitigate spam attacks in wireless sensor networks

The Quarantine Region Scheme (QRS) is introduced to defend against spam attacks in wireless sensor networks where malicious antinodes frequently generate dummy spam messages to be relayed toward the sink. The aim of the attacker is the exhaustion of the sensor node batteries and the extra delay caused by processing the spam messages. Network-wide message authentication may solve this problem with a cost of cryptographic operations to be performed over all messages. QRS is designed to reduce this cost by applying authentication only whenever and wherever necessary. In QRS, the nodes that detect a nearby spam attack assume themselves to be in a quarantine region. This detection is performed by intermittent authentication checks. Once quarantined, a node continuously applies authentication measures until the spam attack ceases. In the QRS scheme, there is a tradeoff between the resilience against spam attacks and the number of authentications. Our experiments show that, in the worst-case scenario that we considered, a not quarantined node catches 80 percent of the spam messages by authenticating only 50 percent of all messages that it processe

Experimental Verification of Cavity-Flow Wall Effects and Correction Rules

This report is intended as a companion to Report No. E-111A.5, "Wall Efects in Cavity Flows", by Wu, Whitney and Lin. Some simple rules for the correction of wall effect are derived from that theoretical study. Experiments designed to complement the theory and to inspect the validity of the correction rules were then carried out in the high-speed water tunnel of the Hydrodynamics Laboratory, California Institute of Technology. The measurements on a series of fully cavitating wedges at zero angle of attack suggested that of the theoretical models that due to Riabouchinsky is superior. They also confirmed the accuracy of the correction rule derived using that model and based on a measurement of the minimum pressure along the tunnel wall

Analysis and performance of the gas-lubricated tilting pad thrust bearing Interim report

Optimal design and performance criteria for gas lubricated tilting pad thrust bearin

The USNO-B Catalog

USNO-B is an all-sky catalog that presents positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 separate observations. The data were obtained from scans of 7,435 Schmidt plates taken for the various sky surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from non-stellar objects. A brief discussion of various issues is given here, but the actual data are available from http://www.nofs.navy.mil and other sites.Comment: Accepted by Astronomical Journa

A Search for Supernova-Remnant Masers Toward Unidentified EGRET Sources

Supernova remnants expanding into adjacent molecular clouds are believed to be sites of cosmic ray acceleration and sources of energetic gamma-rays. Under certain environmental conditions, such interactions also give rise to unusual OH masers in which the 1720 MHz satellite line dominates over the more common 1665/7 MHz emission. Motivated by the apparent coincidence of a handful of EGRET sources with OH(1720 MHz) maser-producing supernova remnants, we have carried out a search using the Very Large Array for new OH(1720 MHz) masers within the error regions of 11 unidentified EGRET sources at low Galactic latitude. While a previously known maser associated with an HII region was serendipitously detected, initial results indicate that no new masers were found down to a limiting flux of, typically, 50 mJy. We discuss the implications of this result on the nature of the unidentified Galactic EGRET sources.Comment: 5 pages, 1 figure. To appear in Proceedings, GAMMA2001 (Baltimore, MD, April 4-6, 2001), eds. N. Gehrels, C. Shrader, and S. Rit

Cyclotron resonant scattering feature simulations. I. Thermally averaged cyclotron scattering cross sections, mean free photon-path tables, and electron momentum sampling

Electron cyclotron resonant scattering features (CRSFs) are observed as absorption-like lines in the spectra of X-ray pulsars. A significant fraction of the computing time for Monte Carlo simulations of these quantum mechanical features is spent on the calculation of the mean free path for each individual photon before scattering, since it involves a complex numerical integration over the scattering cross section and the (thermal) velocity distribution of the scattering electrons. We aim to numerically calculate interpolation tables which can be used in CRSF simulations to sample the mean free path of the scattering photon and the momentum of the scattering electron. The tables also contain all the information required for sampling the scattering electron's final spin. The tables were calculated using an adaptive Simpson integration scheme. The energy and angle grids were refined until a prescribed accuracy is reached. The tables are used by our simulation code to produce artificial CRSF spectra. The electron momenta sampled during these simulations were analyzed and justified using theoretically determined boundaries. We present a complete set of tables suited for mean free path calculations of Monte Carlo simulations of the cyclotron scattering process for conditions expected in typical X-ray pulsar accretion columns (0.01<B/B_{crit}<=0.12, where B_{crit}=4.413x10^{13} G and 3keV<=kT<15keV). The sampling of the tables is chosen such that the results have an estimated relative error of at most 1/15 for all points in the grid. The tables are available online at http://www.sternwarte.uni-erlangen.de/research/cyclo.Comment: A&A, in pres

Bahrain: Reform, Security, and U.S. Policy

[Excerpt] An uprising that began in Bahrain on February 14, 2011, following the revolt that overthrew Egypt’s President Hosni Mubarak three days earlier, began a political crisis that defies resolution. Bahrain’s unrest demonstrates that Shiite grievances over the distribution of power and economic opportunities were not satisfied by the efforts during 1999-2010 to increase the role of the Shiite majority in governance; most Bahraini Shiites now say they seek a constitutional monarchy in which governments are established by an elected parliament. Reflecting increasing polarization, many Sunnis in Bahrain believe the Shiite majority will settle for nothing less than outright rule. As protests escalated in March 2011, Bahrain’s government bucked U.S. advice by inviting direct security assistance from other Gulf Cooperation Council countries, declaring a state of emergency, forcefully suppressing demonstrations, and arresting dissident leaders and pro-opposition health care workers. Although the state of emergency ended on June 1, 2011, the continued imprisonment of dissidents contributed to the resulting failure of a “national dialogue,” held in July 2011, to reach on more than just a few political reform recommendations. Hopes for resolution were raised by a pivotal report by a government-appointed “Independent Commission of Inquiry” (BICI) on the unrest, released November 23, 2011, which was critical of the government’s actions against the unrest as well as the opposition’s responses to government proposals early in the crisis. The government, through an appointed national commission, has begun to implement most of the BICI recommendations, but the stalemate on major political reforms has contributed to the resumption of some renewed violent demonstrations and dashed hopes that a complete solution is in sight. The Obama Administration has not called for a change of the Al Khalifa regime, but it has opposed the regime’s use of force against protesters and urged further and faster political reform. The U.S. position on Bahrain has been criticized by those who believe the United States is downplaying regime abuses because the U.S. security relationship with the Al Khalifa regime is critical to U.S. efforts to contain Iran and preserve security in the Persian Gulf more broadly. In exchange for a tacit security guarantee against Iran or other aggressors, Bahrain has provided key support for U.S. interests by hosting U.S. naval headquarters for the Gulf for over 60 years and by providing facilities and small numbers of personnel for U.S. war efforts in Iraq and Afghanistan. U.S. officials are concerned that the instability in Bahrain could render U.S. use of the naval headquarters facilities untenable, but there are no evident moves to relocate it. Beyond the naval facility, the United States signed a formal defense pact with Bahrain in 1991 and has designated Bahrain as a “major non-NATO ally,” entitling it to sales of sophisticated U.S. weapons systems. Bahrain also receives small amounts of U.S. security assistance. New U.S. sales and aid are coming under criticism from human rights and other groups and, in response, the Administration put on hold a significant proposed sale of armored vehicles and anti-tank weapons while approving smaller sales of military spare parts. Factoring into the U.S. position is a perception that Iran might seek to take advantage of Shiite unrest in Bahrain to reduce U.S. influence and the U.S. military presence in the Persian Gulf. Consumed by its own crisis, Bahrain has joined with but deferred to other GCC powers in initiatives to resolve uprisings in Libya, Syria, and Yemen. Fueling Shiite unrest is the fact that Bahrain, having largely run out of crude oil reserves, is poorer than most of the other Persian Gulf monarchies. The country has tried to compensate through diversification, particularly with banking and some manufacturing. In September 2004, the United States and Bahrain signed a free trade agreement (FTA); legislation implementing itwas signed January 11, 2006 (P.L. 109-169). The unrest in 2011 has further strained Bahrain’s economy

A spy’s guide to Boston University

This article originally appeared in the Vol 23, No 3, Winter 2017-18 edition of AFIO’s Intelligencer journal, which is published by AFIO (Association of Former Intelligence Officers), Falls Church, VA.In this article, Professor John Woodward, a retired CIA officer, examines the people and places associated with Boston University that have made significant, or otherwise interesting, contributions to the world of intelligence