1,680 research outputs found
Searches for Stable Strangelets in Ordinary Matter: Overview and a Recent Example
Our knowledge on the possible existence in nature of stable exotic particles
depends solely upon experimental observation. Guided by this general principle
and motivated by theoretical hypotheses on the existence of stable particles of
strange quark matter, a variety of experimental searches have been performed.
We provide an introduction to the theoretical hypotheses, an overview of the
past searches, and a more detailed description of a recent search for
helium-like strangelets in the Earth's atmosphere using a sensitive laser
spectroscopy method
API design for machine learning software: experiences from the scikit-learn project
Scikit-learn is an increasingly popular machine learning li- brary. Written
in Python, it is designed to be simple and efficient, accessible to
non-experts, and reusable in various contexts. In this paper, we present and
discuss our design choices for the application programming interface (API) of
the project. In particular, we describe the simple and elegant interface shared
by all learning and processing units in the library and then discuss its
advantages in terms of composition and reusability. The paper also comments on
implementation details specific to the Python ecosystem and analyzes obstacles
faced by users and developers of the library
New insights into control of arbovirus replication and spread by insect RNA interference pathways
Arthropod-borne (arbo) viruses are transmitted by vectors, such as mosquitoes, to susceptible vertebrates. Recent research has shown that arbovirus replication and spread in mosquitoes is not passively tolerated but induces host responses to control these pathogens. Small RNA-mediated host responses are key players among these antiviral immune strategies. Studies into one such small RNA-mediated antiviral response, the exogenous RNA interference (RNAi) pathway, have generated a wealth of information on the functions of this mechanism and the enzymes which mediate antiviral activities. However, other small RNA-mediated host responses may also be involved in modulating antiviral activity. The aim of this review is to summarize recent research into the nature of small RNA-mediated antiviral responses in mosquitoes and to discuss future directions for this relatively new area of research
A-dependence of nuclear transparency in quasielastic A(e,e'p) at high Q^2
The A-dependence of the quasielastic A(e,e'p) reaction has been studied at
SLAC with H-2, C, Fe, and Au nuclei at momentum transfers Q^2 = 1, 3, 5, and
6.8 (GeV/c)^2. We extract the nuclear transparency T(A,Q^2), a measure of the
average probability that the struck proton escapes from the nucleus A without
interaction. Several calculations predict a significant increase in T with
momentum transfer, a phenomenon known as Color Transparency. No significant
rise within errors is seen for any of the nuclei studied.Comment: 5 pages incl. 2 figures, Caltech preprint OAP-73
First Measurement of the Atomic Electric Dipole Moment of \u3csup\u3e225\u3c/sup\u3eRa
The radioactive radium-225 (225Ra) atom is a favorable case to search for a permanent electric dipole moment. Because of its strong nuclear octupole deformation and large atomic mass, 225Ra is particularly sensitive to interactions in the nuclear medium that violate both time-reversal symmetry and parity. We have developed a cold-atom technique to study the spin precession of 225Ra atoms held in an optical dipole trap, and demonstrated the principle of this method by completing the first measurement of its atomic electric dipole moment, reaching an upper limit of |d(225Ra)|\u3c5.0×10−22 e cm (95% confidence)
Search for anomalously heavy isotopes of helium in the Earth's atmosphere
Motivated by the theoretical hypotheses on the existence of heretofore
unobserved stable elementary particles and exotic nuclear states, we searched
for doubly-charged particles, as anomalously heavy isotopes of helium, in the
Earth's atmoshpere using a sensitive laser spectroscopy technique. The
concentration of noble-gas-like atoms in the atmosphere and the subsequent very
large depletion of the light He-3,4 isotopes allow us to set stringent limits
on th abundance: 10^-13 to 10^-17 per atom in the solar system, over the mass
range of 20 to 10,000 amu.Comment: 13 pages, 4 figure
Laser Spectroscopic Determination of the 6He Nuclear Charge Radius
We have performed precision laser spectroscopy on individual 6He (t1/2 = 0.8
s) atoms confined and cooled in a magneto-optical trap, and measured the
isotope shift between 6He and 4He to be 43,194.772 +/- 0.056 MHz for the 2 3S1
- 3 3P2 transition. Based on this measurement and atomic theory, the nuclear
charge radius of 6He is determined, for the first time in a method independent
of nuclear models, to be 2.054 +/- 0.014 fm. The result is compared with the
values predicted by a number of nuclear structure calculations, and tests their
ability to characterize this loosely bound, halo nucleus
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