6,168 research outputs found
Sulfur oxidizing capacity of California desert soils
Sulfur oxidation in desert soils due to bacterial activit
Microorganism study - Bacterial isolants from harsh environments Final report
Soil bacterial isolants from harsh environment
Systematic description and key to isolants from Atacama Desert, Chile
Isolation and identification of desert soil microorganism from Chil
Magnetic field stabilization for high-accuracy mass measurements on exotic nuclides
The magnetic-field stability of a mass spectrometer plays a crucial role in
precision mass measurements. In the case of mass determination of short-lived
nuclides with a Penning trap, major causes of instabilities are temperature
fluctuations in the vicinity of the trap and pressure fluctuations in the
liquid helium cryostat of the superconducting magnet. Thus systems for the
temperature and pressure stabilization of the Penning trap mass spectrometer
ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the
fluctuations by at least one order of magnitude downto dT=+/-5mK and
dp=+/-50mtorr has been achieved, which corresponds to a relative frequency
change of 2.7x10^{-9} and 1.5x10^{-10}, respectively. With this stabilization
the frequency determination with the Penning trap only shows a linear temporal
drift over several hours on the 10 ppb level due to the finite resistance of
the superconducting magnet coils.Comment: 23 pages, 13 figure
The Ramsey method in high-precision mass spectrometry with Penning traps: Experimental results
The highest precision in direct mass measurements is obtained with Penning
trap mass spectrometry. Most experiments use the interconversion of the
magnetron and cyclotron motional modes of the stored ion due to excitation by
external radiofrequency-quadrupole fields. In this work a new excitation
scheme, Ramsey's method of time-separated oscillatory fields, has been
successfully tested. It has been shown to reduce significantly the uncertainty
in the determination of the cyclotron frequency and thus of the ion mass of
interest. The theoretical description of the ion motion excited with Ramsey's
method in a Penning trap and subsequently the calculation of the resonance line
shapes for different excitation times, pulse structures, and detunings of the
quadrupole field has been carried out in a quantum mechanical framework and is
discussed in detail in the preceding article in this journal by M. Kretzschmar.
Here, the new excitation technique has been applied with the ISOLTRAP mass
spectrometer at ISOLDE/CERN for mass measurements on stable as well as
short-lived nuclides. The experimental resonances are in agreement with the
theoretical predictions and a precision gain close to a factor of four was
achieved compared to the use of the conventional excitation technique.Comment: 12 pages, 14 figures, 2 table
Human Sexual Cycles are Driven by Culture and Match Collective Moods
It is a long-standing question whether human sexual and reproductive cycles
are affected predominantly by biology or culture. The literature is mixed with
respect to whether biological or cultural factors best explain the reproduction
cycle phenomenon, with biological explanations dominating the argument. The
biological hypothesis proposes that human reproductive cycles are an adaptation
to the seasonal cycles caused by hemisphere positioning, while the cultural
hypothesis proposes that conception dates vary mostly due to cultural factors,
such as vacation schedule or religious holidays. However, for many countries,
common records used to investigate these hypotheses are incomplete or
unavailable, biasing existing analysis towards primarily Christian countries in
the Northern Hemisphere. Here we show that interest in sex peaks sharply online
during major cultural and religious celebrations, regardless of hemisphere
location. This online interest, when shifted by nine months, corresponds to
documented human birth cycles, even after adjusting for numerous factors such
as language, season, and amount of free time due to holidays. We further show
that mood, measured independently on Twitter, contains distinct collective
emotions associated with those cultural celebrations, and these collective
moods correlate with sex search volume outside of these holidays as well. Our
results provide converging evidence that the cyclic sexual and reproductive
behavior of human populations is mostly driven by culture and that this
interest in sex is associated with specific emotions, characteristic of, but
not limited to, major cultural and religious celebrations.Comment: Main Paper: 21 pages, 4 figures Supplementary Material: 66 pages, 15
figures, 13 table
Biologically Motivated Distributed Designs for Adaptive Knowledge Management
We discuss how distributed designs that draw from biological network
metaphors can largely improve the current state of information retrieval and
knowledge management of distributed information systems. In particular, two
adaptive recommendation systems named TalkMine and @ApWeb are discussed in more
detail. TalkMine operates at the semantic level of keywords. It leads different
databases to learn new and adapt existing keywords to the categories recognized
by its communities of users using distributed algorithms. @ApWeb operates at
the structural level of information resources, namely citation or hyperlink
structure. It relies on collective behavior to adapt such structure to the
expectations of users. TalkMine and @ApWeb are currently being implemented for
the research library of the Los Alamos National Laboratory under the Active
Recommendation Project. Together they define a biologically motivated
information retrieval system, recommending simultaneously at the level of user
knowledge categories expressed in keywords, and at the level of individual
documents and their associations to other documents. Rather than passive
information retrieval, with this system, users obtain an active, evolving
interaction with information resources.Comment: To appear in Design Principles for the Immune System and Other
Distributed Autonomous Systems. i. Cohen and L. Segel (Eds.). Oxford
University Pres
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