176 research outputs found
Compression of Ultrashort Laser Pulses via Gated Multiphoton Intrapulse Interference Phase Scans
Delivering femtosecond laser light in the focal plane of a high numerical
aperture microscope objective is still a challenge, despite significant
developments in the generation of ultrashort pulses. One of the most popular
techniques, used to correct phase distortions resulting from propagation
through transparent media, is the multiphoton intrapulse interference phase
scan (MIIPS). The accuracy of MIIPS however is limited when higher order phase
distortions are present. Here we introduce an improvement, called Gated-MIIPS,
which avoids shortcomings of MIIPS, reduces the influence of higher order phase
terms, and can be used to more efficiently compress broad band laser pulses
even with a simple 4f pulse shaper setup. In this work we present analytical
formulas for MIIPS and Gated-MIIPS valid for chirped Gaussian pulses; we show
an approximated analytic expression for Gated-MIIPS valid for arbitrary pulse
shapes; finally we demonstrate the increased accuracy of Gated-MIIPS via
experiment and numerical simulation.Comment: 11 pages, 7 figure
Effect of different pastures on CLA content in milk and sheep cheese
It is known that milk composition included conjugated linoleic acid (CLA) is affected by animal feeding system (Cabiddu et al., 2001). In Sardinia dairy sheep feeding is mainly based on pastures. Most of them are characterised by self-regenerating species, like annual ryegrass (Lolium rigidum Gaudin) and burr medic (Medicago polymorpha L.). Non conventional species belonging to the Compositae family such as (Chrysanthemum coronarium L.) seem interesting for sheep feeding when other herbages decrease in quality (late spring- early summer). It was observed that C. coronarium establishes rapidly, can be grazed early in the growing season and persist where other pasture species
may disappear; for these reasons it can be considered a valuable source of food. Moreover a preliminary
study with dairy sheep fed fresh forage of C. coronarium showed relatively high levels of CLA in milk
(Molle G. pers. com.) The aim of the present work was to study the influence of different pastures on milk composition, with particular reference to CLA and its precursors
Los Bronces antropomorfos sardos de la Cerdeña nurágica
Il proposito di questo lavoro è quello di fornire un quadro d’insieme delle società sarde e del loro percorso storico nei primi secoli del primo millennio a.C. attraverso lo studio della piccola plastica antropomorfa il cui repertorio figurativo, insieme alle altre categorie di oggetti di bronzo destinato ad essere accolte nei luoghi di culto, costituisce una fonte di informazione di grande importanza relativamente al modo in cui gli antichi abitanti dell’isola rappresentavano il loro sistema di valori, gli equilibri tra le differenti componenti sociali ed il rapporto con il mondo degli esseri supremi e degli antenati. Il catalogo dei reperti integra il corpus dei bronzetti pubblicato nel 1966 da Lilliu con esemplari di recente acquisizione alcuni dei quali ancora inediti
Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand
Entangled photon generation from semiconductor quantum dots via the
biexciton-exciton cascade underlies various decoherence mechanisms related to
the solid-state nature of the quantum emitters. So far, this has prevented the
demonstration of nearly-maximally entangled photons without the aid of
inefficient and complex post-selection techniques that are hardly suitable for
quantum communication technologies. Here, we tackle this challenge using
strain-tunable GaAs quantum dots driven under two-photon resonant excitation
and with strictly-degenerate exciton states. We demonstrate experimentally that
our on-demand source generates polarization-entangled photons with fidelity of
0.978(5) and concurrence of 0.97(1) without resorting to post-selection
techniques. Moreover, we show that the remaining decoherence mechanisms can be
overcome using a modest Purcell enhancement so as to achieve a degree of
entanglement >0.99. Our results highlight that GaAs quantum dots can be readily
used in advanced communication protocols relying on the non-local properties of
quantum entanglement
A frequency-tunable nanomembrane mechanical oscillator with embedded quantum dots
Hybrid systems consisting of a quantum emitter coupled to a mechanical
oscillator are receiving increasing attention for fundamental science and
potential applications in quantum technologies. In contrast to most of the
presented works, in which the oscillator eigenfrequencies are irreversibly
determined by the fabrication process, we present here a simple approach to
obtain frequency-tunable mechanical resonators based on suspended
nanomembranes. The method relies on a micromachined piezoelectric actuator,
which we use both to drive resonant oscillations of a suspended Ga(Al)As
membrane with embedded quantum dots and to fine tune their mechanical
eigenfrequencies. Specifically, we excite oscillations with frequencies of at
least 60 MHz by applying an AC voltage to the actuator and tune the
eigenfrequencies by at least 25 times their linewidth by continuously varying
the elastic stress state in the membranes through a DC voltage. The light
emitted by optically excited quantum dots is used as sensitive local strain
gauge to monitor the oscillation frequency and amplitude. We expect that our
method has the potential to be applicable to other optomechanical systems based
on dielectric and semiconductor membranes possibly operating in the quantum
regime.Comment: 17 pages, 4 figure
Ex situ phytoremediation trial of Sardinian mine waste using a pioneer plant species
The mitigation of metals contamination is currently a crucial issue for the reclamation of mine sites. Indeed, mine wastes are often disposed in open dumps and consequently pollutants are subjected to dispersion in the surrounding areas. In this study, the potential use of Helichrysum microphyllum subsp. tyrrhenicum for phytostabilization was evaluated in ex situ conditions. Ninety specimens were randomly selected and were planted in three substrates (reference substrate, mine waste materials, and mine wastes with compost). Mineralogical compositions of substrates, rhizosphere, and roots were assessed through X-ray diffraction (XRD). Zn, Pb, and Cd concentrations of substrates, rhizosphere, soil pore waters, and plant tissues were determined. The phytostabilization potential was determined through the application of biological accumulation coefficient (BAC), biological concentration factor (BCF), and translocation factor (TF). Moreover, survival and biometric parameters were assessed on plant specimens. The polluted substrates and related rhizosphere materials were mainly composed of dolomite, quartz, pyrite, and phyllosilicate. Zn was the most abundant metal in substrates, rhizosphere, and soil pore waters. XRD analysis on roots showed the presence of amorphous cellulose and quartz and Zn was the most abundant metal in plant tissues. H. microphyllum subsp. tyrrhenicum restricts the accumulation of the metals into roots limiting their translocation in aereal parts, indicating its potential use as phytostabilizer (BCF, BAC, TF < 1). Survival and growth data showed a great adaptability to different substrates, with an evident positive effect of the implementation of compost which increased the plant survival and decreased the metals uptake into roots
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Wavelength-tunable sources of entangled photons interfaced with atomic vapours
The prospect of using the quantum nature of light for secure communication keeps spurring
the search and investigation of suitable sources of entangled photons. A single semiconductor
quantum dot is one of the most attractive, as it can generate indistinguishable
entangled photons deterministically and is compatible with current photonic-integration
technologies. However, the lack of control over the energy of the entangled photons is
hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation
of quantum entanglement over remote locations. Here we introduce quantum dot-based
sources of polarization-entangled photons whose energy can be tuned via three-directional
strain engineering without degrading the degree of entanglement of the photon pairs. As a
test-bench for quantum communication, we interface quantum dots with clouds of atomic
vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These
results pave the way towards the implementation of hybrid quantum networks where
entanglement is distributed among distant parties using optoelectronic devices
A Survey on the milk fatty acid composition of forty dairy sheep flocks in Sardinia
A survey was carried out to monitor milk fatty acid (FA) composition during two years (2003 and
2004) on forty dairy sheep flocks, fed pasture based rations, in 5 macro pedoclimatic areas of Sardinia, featured by
different i) soil type, (granitic, G; basaltic, B and alluvial, A) ii) average annual rainfall (low, L, 500-600 mm/year;
high, H, 600-800 mm/year). Milk FA profile was strongly influenced by year. In particular milk linolenic acid (LN),
CLA (conjugated linoeic acid) and PUFA (polyunsaturated fatty acids) levels increased (by 25, 30 and 14%, respectively,
P<0.01) whereas the atherogenicity index (AI) decreased (by 8%, P<0.01) in all areas in 2004 as compared with
2003. Pedoclimatic area affected milk fatty acid composition (P<0.01). In both years milk from AL farms showed the
highest levels of LN, CLA and PUFA. AI was lower in BH and GH in year 2003 and in BH, AH and GL in 2004
X-ray phase-contrast microtomography of soft tissues using a compact laboratory system with two-directional sensitivity
X-ray microtomography is a nondestructive, three-dimensional inspection technique applied across a vast range of fields and disciplines, ranging from research to industrial, encompassing engineering, biology, and medical research. Phase-contrast imaging extends the domain of application of x-ray microtomography to classes of samples that exhibit weak attenuation, thus appearing with poor contrast in standard x-ray imaging. Notable examples are low-atomic-number materials, like carbon-fiber composites, soft matter, and biological soft tissues. We report on a compact and cost-effective system for x-ray phase-contrast microtomography. The system features high sensitivity to phase gradients and high resolution, requires a low-power sealed x-ray tube, a single optical element, and fits in a small footprint. It is compatible with standard x-ray detector technologies: in our experiments, we have observed that single-photon counting offered higher angular sensitivity, whereas flat panels provided a larger field of view. The system is benchmarked against known-material phantoms, and its potential for soft-tissue three-dimensional imaging is demonstrated on small-animal organs: a piglet esophagus and a rat heart. We believe that the simplicity of the setup we are proposing, combined with its robustness and sensitivity, will facilitate accessing quantitative x-ray phase-contrast microtomography as a research tool across disciplines, including tissue engineering, materials science, and nondestructive testing in general
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