Measuring the effective phonon density of states of a quantum dot

We employ detuning-dependent decay-rate measurements of a quantum dot in a photonic-crystal cavity to study the influence of phonon dephasing in a solid-state quantum-electrodynamics experiment. The experimental data agree with a microscopic non-Markovian model accounting for dephasing from longitudinal acoustic phonons, and identifies the reason for the hitherto unexplained difference between non-resonant cavity feeding in different nanocavities. From the comparison between experiment and theory we extract the effective phonon density of states experienced by the quantum dot. This quantity determines all phonon dephasing properties of the system and is found to be described well by a theory of bulk phonons.Comment: 5 pages, 3 figures, submitte

Induced radioactivity in AB-BNCT: an analysis of the different facilities worldwide

The global effort to establish Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT) facilities involves various accelerator technologies and neutron-producing targets, each characterized by different properties of the primary beam and neutron spectra they generate. With an emphasis on long-term sustainability, it is essential to minimize the production of residual radioactivity to the lowest possible level, particularly given their intended use in a hospital environment. This paper aims to quantitatively assess the residual radioactivity in these facilities, taking into account both primary and secondary activation. Primary activation primarily arises from the interaction of the proton or deuteron beam and the neutron-producing target. Secondary activation results from neutron-induced reactions on the elements exposed to the neutron flux, with the Beam Shaping Assembly (BSA) being the most exposed one. To assess activation, we evaluated a representative group of target-BSA configurations. Primary activation was calculated based on cross-sectional data and the corresponding target materials. Neutron activation was assessed using Monte Carlo simulations with the MCNP 6.1 code. Regarding target activation, our findings indicate that 9Be targets working with protons of less than 10 MeV represent the cleanest option, while 7Li targets working with protons lead to the highest activation levels. As for BSA activation, the neutron energy is a crucial factor. In the case of standard BSA materials, higher neutron energy results in an increased number of potential reactions that produce radioactive products. Additionally, our findings suggest that radioactivity induced by impurities and minor components in alloyed materials cannot be disregarded and must be taken into account in radioactivity calculations. In summary, this research provides a comprehensive analysis of activation of the commonly used targets and BSA materials, aimed at contributing to the optimization of AB-BNCT facilities from a radiological perspective

The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau

We have carried out an analysis of about 160 eclipse timings spanning over 30 years of the Hyades eclipsing binary V471 Tauri that shows a long-term quasi-sinusoidal modulation of its observed eclipse arrival times. The O-Cs have been analyzed for the ``light-time'' effect that arises from the gravitational influence of a tertiary companion. The presence of a third body causes the relative distance of the eclipsing pair to the Earth to change as it orbits the barycenter of the triple system. The result of the analysis of the eclipse times yields a light-time semi-amplitude of 137.2+/-12.0 s, an orbital period of P_3 = 30.5+/-1.6 yr and an eccentricity of e_3 = 0.31+/-0.04. The mass of the tertiary component is M_3 sin i_3 = 0.0393+/-0.0038 Mo when a total mass of 1.61+/-0.06 Mo for V471 Tau is adopted. For orbital inclinations i_3 > 35 deg, the mass of the third body would be below the stable hydrogen burning limit of M = 0.07 Mo and it thus would be a brown dwarf. In the next several years (near maximum elongation), it should be feasible to obtain IR images and spectra of V471 Tau C that, when combined with the known mass, age, distance, and [Fe/H], will serve as a benchmark for understanding the physical properties and evolution of brown dwarfs.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter

A Search for Hierarchical Triples using Kepler Eclipse Timing

We present the first results of a Kepler survey of 41 eclipsing binaries that we undertook to search for third star companions. Such tertiaries will periodically alter the eclipse timings through light travel time and dynamical effects. We discuss the prevalence of starspots and pulsation among these binaries and how these phenomena influence the eclipse times. There is no evidence of short period companions (P < 700 d) among this sample, but we do find evidence for long term timing variations in 14 targets (34%). We argue that this finding is consistent with the presence of tertiary companions among a significant fraction of the targets, especially if many have orbits measured in decades. This result supports the idea that the formation of close binaries involves the deposition of angular momentum into the orbital motion of a third star.Comment: AJ, in press, 104 pages, 2 figure sets plus 1 regular figur

Impacts of Land Abandonment on Vegetation: Successional Pathways in European Habitats

Changes in traditional agricultural systems in Europe in recent decades have led to widespread abandonment and colonization of various habitats by shrubs and trees. We combined several vegetation databases to test whether patterns of changes in plant diversity after land abandonment in different habitats followed similar pathways. The impacts of land abandonment and subsequent woody colonization on vegetation composition and plant traits were studied in five semi-natural open habitats and two arable habitats in six regions of Europe. For each habitat, vegetation surveys were carried out in different stages of succession using either permanent or non-permanent plots. Consecutive stages of succession were defined on a physiognomic basis from initial open stages to late woody stages. Changes in vegetation composition, species richness, numbers of species on Red Lists, plant strategy types, Ellenberg indicator values of the vegetation, Grime CSR strategy types and seven ecological traits were assessed for each stage of the successional pathway. Abandonment of agro-pastoral land-use and subsequent woody colonization were associated with changes in floristic composition. Plant richness varied according to the different habitats and stages of succession, but semi-natural habitats differed from arable fields in several ecological traits and vegetation responses. Nevertheless, succession occurred along broadly predictable pathways. Vegetation in abandoned arable fields was characterized by a decreasing importance of R-strategists, annuals, seed plants with overwintering green leaves, insect-pollinated plants with hemi-rosette morphology and plants thriving in nutrient-rich conditions, but an increase in species considered as endangered according to the Red Lists. Conversely, changes in plant traits with succession within the initially-open semi-natural habitats showed an increase in plants thriving in nutrient-rich conditions, stress-tolerant plants and plants with sexual and vegetative reproduction, but a sharp decrease in protected species. In conclusion, our study showed a set of similarities in responses of the vegetation in plant traits after land abandonment, but we also highlighted differences between arable fields and semi-natural habitats, emphasizing the importance of land-use legacy

Risk-based surveillance for human health hazards: the example of Trichinella

Increasing demands for cost-effectiveness in surveillance for human health hazards can be met by introducmg risk-based principles. This implies targeting subpopulations w1th higher risk of infection compared to the whole population. We demonstrate how historical data from surveillance can be used to assess risk of infection. The model is called Discounting historical evidence and depends mainly on two variables: Annual risk of introduction Plntro and surveillance system sensitivity SSe (ability to detect infection if present). The model Implies simulations that reiterate for a number of years, and for each year the output is updated with the confidence on absence of infection. Trichinella spiralis infection in pigs is used as an example. In Denmark, pigs at slaughter are tested (currently 23 million per year), and despite of \u3e 70 years of sampling no pigs have been found positive. Hence, we concluded that Plntro is low. SSe can be estimated from the maximum number of infected carcasses expected under the specified design prevalence, and the sensitivity of the test applied. According to the assessment, the prevalence of Trichmella in Danish pigs is negligible (\u3c1 case/million). Based on this , a risk-based surveillance programme for Trichinella is designed that targets all out-door reared pigs as well as all sows and boars (currently 610,000 per year). Compared to confined pigs, outdoor-reared pigs have higher risk of getting Trichinella because of their exposure to wildlife, which might harbour Trichinella. Sows and boars are at increased risk, because they live longer than fimshers. Again, SSe and Plntro are estimated and the model is used to show how risk-based surveillance can be applied without jeopardizing human health. Finally, we incorporate wildlife surveys and test quality assurance in the programme. The model results are included in an application to the European Commission concern1ng Denmark\u27s status as a region with negligible risk of Trichinella

Magnetism in Nb(1-y)Fe(2+y) - composition and magnetic field dependence

We present a systematic study of transport and thermodynamic properties of the Laves phase system Nb$_{1-y}$Fe$_{2+y}$. Our measurements confirm that Fe-rich samples, as well as those rich in Nb (for $\mid y\mid\geq 0.02$), show bulk ferromagnetism at low temperature. For stoichiometric NbFe$_2$, on the other hand, magnetization, magnetic susceptibility and magnetoresistance results point towards spin-density wave (SDW) order, possibly helical, with a small ordering wavevector $Q \sim 0.05$ \AA$^{-1}$. Our results suggest that on approaching the stoichiometric composition from the iron-rich side, ferromagnetism changes into long-wavelength SDW order. In this scenario, $Q$ changes continuously from 0 to small, finite values at a Lifshitz point in the phase diagram, which is located near $y=+0.02$. Further reducing the Fe content suppresses the SDW transition temperature, which extrapolates to zero at $y\approx -0.015$. Around this Fe content magnetic fluctuations dominate the temperature dependence of the resistivity and of the heat capacity which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point. Because the critical point is located between the SDW phase associated with stoichiometric NbFe$_2$ and the ferromagnetic order which reemerges for very Nb-rich NbFe$_2$, the observed temperature dependences could be attributed both to proximity to SDW order or to ferromagnetism.Comment: 13 pages, 20 figure

Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus

Up to now, V382 Cyg and TU Mus are the only two discovered O-type overcontact binary stars with periods less than two days (P = 1.8855 and 1.3873 d). Both systems contain a visual companion. New eclipse times and analyses of orbital period variations of the two systems are presented. It is discovered that the periods of both binaries show cyclic oscillations with periods of 47.70 and 47.73 yr, while they undergo continuous increases at rates of dP/dt = +4.4 × 10−7 and +4.0 × 10−7 d yr−1, respectively. The periodic variations can be interpreted as light travel times effects caused by the presence of invisible tertiary components suggesting that they may be quadruple systems. It is possible that the additional bodies may play an important role in the formation and evolution of the two massive overcontact binaries by removing angular momentum from the central systems, and causing the eclipsing pairs to have lower angular momentum and shorter initial orbital periods. In this way, the original detached systems can evolve into the present overcontact configurations via a Case A mass transfer. This is in agreement with the observed long-term period increase of V382 Cyg and TU Mus, which can be explained by mass transfers from the less massive components to the more massive ones. It is found that the time-scales of the long-term period variations of both systems are much longer than the thermal time-scales of the secondary components, but are close to their nuclear time-scales. This suggests that the two massive binaries have been through the rapid mass-transfer evolutionary stage on the thermal time-scales of the secondaries, and they are now on the slow phase of Case A mass transfer. It is shown that massive overcontact binaries are going through a short-lived overcontact configuration during the evolutionary phases of Case A mass transfer, which is different from the situation of late-type overcontact binary stars where components remain in good overcontact configuration driving by a combination of thermal relaxation oscillation and variable angular momentum loss via change in overcontact depth. This conclusion is in agreement with the distribution of overcontact binary stars along with the orbital period.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat