174 research outputs found
Magnetically Stabilized Luminescent Excitations in Hexagonal Boron Nitride
Magnetically stabilized luminescence is observed in hexagonal boron nitride.
The luminescence is induced by absorption of cold neutrons and is in the
visible region. In the absence of a magnetic field, the photon emission level
is observed to decay over several hundred seconds. A fraction of this
luminescence can be suppressed if the temperature is T <~ 0.6 K and the
magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression,
luminescence can be induced by an increase in T or lowering of B. Possible
explanations include stabilization of triplet states or the localization and
stabilization of excitons.Comment: 11 pages, 7 figures, to appear in the Journal of Luminescenc
New Dihydroxytyrosyl Esters from Dicarboxylic Acids: Synthesis and Evaluation of the Antioxidant Activity In Vitro (ABTS) and in Cell-Cultures (DCF Assay)
New dihydroxytyrosyl esters 2a, 2c-2j of dicarboxylic acids were synthesized from methyl orthoformate protected hydroxytyrosol 3 and diacyl chlorides. New compounds were characterized (HRMS, FT-IR, 1H- and 13C-NMR), and tested for antioxidant activity both in vitro (ABTS) and on L6 myoblasts and THP1 leukemic monocytes cell culture by DCF assay. According to the ABTS assay, compounds 2a, 2c-2j showed a TEAC value of antioxidant capacity up to twice that of Trolox. Very high or complete ROS protections were obtained in the cell environment where lipophilicity and rigidity of dicarboxylic structure seem to facilitate the antioxidant effect. MTT assay and proliferation test were used for assessment of cell viability. These compounds can be envisaged as a new class of preservatives for food or cosmetic products
Magnetic trapping of ultracold neutrons
Three-dimensional magnetic confinement of neutrons is reported. Neutrons are
loaded into an Ioffe-type superconducting magnetic trap through inelastic
scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low
energy and in the appropriate spin state are confined by the magnetic field
until they decay. The electron resulting from neutron decay produces
scintillations in the liquid helium bath that results in a pulse of extreme
ultraviolet light. This light is frequency downconverted to the visible and
detected. Results are presented in which 500 +/- 155 neutrons are magnetically
trapped in each loading cycle, consistent with theoretical predictions. The
lifetime of the observed signal, 660 s +290/-170 s, is consistent with the
neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review
Mean Field Theory of Josephson Junction Arrays with Charge Frustration
Using the path integral approach, we provide an explicit derivation of the
equation for the phase boundary for quantum Josephson junction arrays with
offset charges and non-diagonal capacitance matrix. For the model with nearest
neighbor capacitance matrix and uniform offset charge , we determine,
in the low critical temperature expansion, the most relevant contributions to
the equation for the phase boundary. We explicitly construct the charge
distributions on the lattice corresponding to the lowest energies. We find a
reentrant behavior even with a short ranged interaction. A merit of the path
integral approach is that it allows to provide an elegant derivation of the
Ginzburg-Landau free energy for a general model with charge frustration and
non-diagonal capacitance matrix. The partition function factorizes as a product
of a topological term, depending only on a set of integers, and a
non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure
15 years of protest and media technologies scholarship: A sociotechnical timeline
This article investigates the relationship between the invention of new media technologies and scholarship concerning protest and political engagement. Building on an innovative approach that moves beyond a systematic literature review, this article contributes to our understanding of scholarship concerning digital communication technologies and how they may have been adopted and shaped protest movements and political engagement. Based on visualizations, we draw a sociotechnical timeline of protest and media technology scholarship within three dimensions: technological development, methods and techniques, and the social phenomena under investigation. The article concludes by identifying major trends in protest and media technologies scholarship over the past 15 years. The sociotechnical timeline enhances our understanding of academic discourse at the intersection of protest and media technologies by highlighting shortcomings and potential for future research
Bottom-up assembly of metallic germanium
Extending chip performance beyond current limits of miniaturisation requires new materials and functionalities that integrate well with the silicon platform. Germanium fits these requirements and has been proposed as a high-mobility channel material, a light emitting medium in silicon-integrated lasers, and a plasmonic conductor for bio-sensing. Common to these diverse applications is the need for homogeneous, high electron densities in three-dimensions (3D). Here we use a bottom-up approach to demonstrate the 3D assembly of atomically sharp doping profiles in germanium by a repeated stacking of two-dimensional (2D) high-density phosphorus layers. This produces high-density (1019 to 1020 cm-3) low-resistivity (10-4Ω ∙ cm) metallic germanium of precisely defined thickness, beyond the capabilities of diffusion-based doping technologies. We demonstrate that free electrons from distinct 2D dopant layers coalesce into a homogeneous 3D conductor using anisotropic quantum interference measurements, atom probe tomography, and density functional theory
“I luoghi di Mercalli”: a travelling exhibition as a tool for scientists to dialogue with the public on volcanoes and earthquakes
On March 19, 1914 Giuseppe Mercalli, a seismologist and volcanologist, well-known around the world for the
Intensity scale of earthquakes bearing his name, died tragically. A hundred years after, the Istituto Nazionale di
Geofisica e Vulcanologia (INGV) has promoted a variety of activities and cultural events that will take place under the
Patronage of the President of the Italian Republic within a year, the so called “Anno Mercalliano” (the Year of
Mercalli).
The opening ceremony took place in Naples, Italy, on March 19, 2014, in the Convitto Nazionale Vittorio Emanuele
II. A scientific conference was held with the participation of experts from INGV and the university of Milano –
Bicocca, and presentations of students. On that day the exhibition entitled “I luoghi di Mercalli” (Mercalli's places) was
also inaugurated, at the presence of local authorities.
The exhibition, organized by INGV, was realized in collaboration with the high school Vittorio Emanuele II, where
Mercalli has been teaching for 19 years, and the Università degli Studi Suor Orsola Benincasa, where he was professor
of natural sciences.
A biographical and geographical description of the places where Mercalli operated introduces the exhibition, which
is organized in sections:
- Mercalli educator (he taught at high schools in Reggio Calabria and Naples);
- Mercalli volcanologist (Mercalli studied Vesuvius volcanic activity for more than twenty years, he was a scientific
witness of the Vesuvius 1906 eruption, and of the eruptions occurred at Vulcano (1888-90) and Stromboli (1891)
islands.
- Mercalli seismologist (Mercalli Intensity scale definition, based on his experience as witness of catastrophic
earthquakes, such as Casamicciola in 1883 and Messina in 1908).
Another section deals with the Vesuvius Observatory, directed by Mercalli between 1911 and 1914, and the
description of the three active volcanoes of the Campania region (Vesuvius, Campi Flegrei and Ischia island), which
have been the subject of studies by the well-known scientist. The exhibition is enriched by documents, manuscripts,
photos and field notebooks of Mercalli.
It is not intended to be only a celebratory exhibition; rather it is designed as a tool for dissemination of scientific
culture and to raise awareness about seismic and volcanic hazards.
In the exhibition path a continuous thread between the figure of Mercalli as a researcher and the role of an Earth
Science researcher today is highlighted, pointing to the development of scientific knowledge in the past century. The
goal is to improve the capability of learning from the disasters occurred in the past to implement preventive actions to
safely deal with future events.
The exhibition is travelling and will be provided on request to institutions and schools.PublishedMilano, Italia1V. Storia e struttura dei sistemi vulcaniciope
Measuring the Neutron Lifetime Using Magnetically Trapped Neutrons
The neutron beta-decay lifetime plays an important role both in understanding
weak interactions within the framework of the Standard Model and in theoretical
predictions of the primordial abundance of 4He in Big Bang Nucleosynthesis. In
previous work, we successfully demonstrated the trapping of ultracold neutrons
(UCN) in a conservative potential magnetic trap. A major upgrade of the
apparatus is nearing completion at the National Institute of Standards and
Technology Center for Neutron Research (NCNR). In our approach, a beam of 0.89
nm neutrons is incident on a superfluid 4He target within the minimum field
region of an Ioffe-type magnetic trap. A fraction of the neutrons is
downscattered in the helium to energies <200 neV, and those in the appropriate
spin state become trapped. The inverse process is suppressed by the low phonon
density of helium at temperatures less than 200 mK, allowing the neutron to
travel undisturbed. When the neutron decays the energetic electron ionizes the
helium, producing scintillation light that is detected using photomultiplier
tubes. Statistical limitations of the previous apparatus will be alleviated by
significant increases in field strength and trap volume resulting in twenty
times more trapped neutrons.Comment: 5 pages, 5 figure
Quantum computation based on d-level cluster states
The concept of qudit (a d-level system) cluster state is proposed by
generalizing the qubit cluster state (Phys. Rev. Lett. \textbf{86}, 910 (2001))
according to the finite dimensional representations of quantum plane algebra.
We demonstrate their quantum correlations and prove a theorem which guarantees
the availability of the qudit cluster states in quantum computation. We
explicitly construct the network to show the universality of the one-way
computer based on the defined qudit cluster states and single-qudit
measurement. And the corresponding protocol of implementing one-way quantum
computer can be suggested with the high dimensional "Ising" model which can be
found in many magnetic systems.Comment: Revtex4, 15 pages, 3 eps figure
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