Search for Supernova Neutrino-Bursts with the AMANDA Detector

The core collapse of a massive star in the Milky Way will produce a neutrino burst, intense enough to be detected by existing underground detectors. The AMANDA neutrino telescope located deep in the South Pole ice can detect MeV neutrinos by a collective rate increase in all photo-multipliers on top of dark noise. The main source of light comes from positrons produced in the CC-reaction of anti-electron neutrinos on free protons \antinue + p \to e^+ + n. This paper describes the first supernova search performed on the full sets of data taken during 1997 and 1998 (215 days of live time) with 302 of the detector's optical modules. No candidate events resulted from this search. The performance of the detector is calculated, yielding a 70% coverage of the Galaxy with one background fake per year with 90% efficiency for the detector configuration under study. An upper limit at the 90% c.l. on the rate of stellar collapses in the Milky Way is derived, yielding 4.3 events per year. A trigger algorithm is presented and its performance estimated. Possible improvements of the detector hardware are reviewed.Comment: 20 pages, 14 figures. Submitted to Astroparticle Physic

Phosphate insensitive aminophosphonate mineralisation within oceanic nutrient cycles

Many areas of the ocean are nutrient-poor yet support large microbial populations, leading to intense competition for and recycling of nutrients. Organic phosphonates are frequently found in marine waters, but require specialist enzymes for catabolism. Previous studies have shown that the genes which encode these enzymes in marine systems are under Pho regulon control and so are repressed by inorganic phosphate. This has led to the conclusion that phosphonates are recalcitrant in much of the ocean where phosphorus is not limiting despite the degradative genes being common throughout the marine environment. Here we challenge this paradigm and show, for the first time, that bacteria isolated from marine samples have the ability to mineralise 2-aminoethylphosphonate, the most common biogenic marine aminophosphonate, via substrate-inducible gene regulation rather than via Pho-regulated metabolism. Substrate-inducible, Pho-independent 2-aminoethylphosphonate catabolism therefore represents a previously unrecognised component of the oceanic carbon, nitrogen and phosphorus cycles

A Three-Level Approach for Analyzing User Behavior in Ongoing Relationships

Peer-reviewedThis paper describes a hybrid methodology to study users in ongoing relationships based on three levels of user data analysis

Nonbinary audio cryptography

Visual cryptography, introduced by Naor-Shamir at Eurocrypt '94, only requires primitive technology to decrypt the ciphertext. However, a disadvantage of it is that the "ciphertext", as a random looking transparency, is suspicious to a censor. The solutions recently proposed by Desmedt-Hou-Quisquater to avoid these problems are neither user friendly, having a low bandwidth, nor are tested. In this paper we present three schemes that overcome these problems. As in one of the Desmedt-Hou-Quisquater's schemes, a share (or a ciphertext) corresponds to an audio signal, such as music. While in the Desmedt-Hou-Quisquater scheme the plaintext was binary, in our schemes the plaintext can also be speech, or any other audio signal. By introducing variations of the one-time pad we guarantee perfect secrecy. The ciphertext is nonsuspicious, when tested with human ears, is indistinguishable from normal music