Search

The CHIPS R&D project focuses on development of low-cost water Cherenkov neutrino detectors through novel design strategies and resourceful engineering. This work presents an end-to-end DAQ solution intended for a recent 5 kt CHIPS prototype, which is largely based on affordable mass-produced components. Much like the detector itself, the presented instrumentation is composed of modular arrays that can be scaled up and easily serviced. A single such array can carry up to 30 photomultiplier tubes (PMTs) accompanied by electronics that generate high voltage in-situ and deliver time resolution of up to 0.69 ns. In addition, the technology is compatible with the White Rabbit timing system, which can synchronize its elements to within 100 ps. While deployment issues did not permit the presented DAQ system to operate beyond initial evaluation, the presented hardware and software successfully passed numerous commissioning tests that demonstrated their viability for use in a large-scale neutrino detector, instrumented with thousands of PMTs., Comment: 30 pages, 28 figures, submitted to MDPI Applied Sciences, Special Issue: Advanced Neutrino Detector Development and Application

Energy sustainability and interconnectivity are the two main pillars on which cutting-edge architecture is based and require the realisation of energy and intelligent devices that can be fully integrated into buildings, capable of meeting stringent regulatory requirements and operating in real-world conditions. Luminescent solar concentrators, particularly those based on near-infrared emitting reabsorption-free quantum dots, are considered good candidates for the realisation of semi-transparent photovoltaic glazing, but despite important advances in optical property engineering strategies, studies of finished devices suitable for real-world operation are still lacking. In this paper, we demonstrate the first example of a fully assembled quantum dot luminescent solar concentrator-based photovoltaic glazing that meets all international standards for photovoltaic and building elements. We also show that these devices are capable of functioning as efficient Visible Light Communication (VLC) receivers even under full sunlight, thus combining energy and wireless connectivity functions in a realistic solution for smart, sustainable buildings.

CHIPS (CHerenkov detectors In mine PitS) was a prototype large-scale water Cherenkov detector located in northern Minnesota. The main aim of the R&D project was to demonstrate that construction costs of neutrino oscillation detectors could be reduced by at least an order of magnitude compared to other equivalent experiments. This article presents design features of the CHIPS detector along with details of the implementation and deployment of the prototype. While issues during and after the deployment of the detector prevented data taking, a number of key concepts and designs were successfully demonstrated.

It is known that, for the algebra of functions on a Kleinian singularity, the parameter space of deformations and the parameter space of quantizations coincide. We prove that, for a Kleinian singularity of type $\mathbf{A}$ or $\mathbf{D}$, isomorphisms between the quantizations are essentially the same as Poisson isomorphisms between deformations. In particular, the group of automorphisms of the deformation and the quantization corresponding to the same deformation parameter are isomorphic. We additionally describe the groups of automorphisms as abstract groups: for type $\mathbf{A}$ they have an amalgamated free product structure, for type $\mathbf{D}$ they are subgroups of the groups of Dynkin diagram automorphisms. For type $\mathbf{D}$ we also compute all the possible affine isomorphisms between deformations; this was not known before., Comment: Corrected typos

We introduce the notion of a $\hbar$-vertex algebra, which is an algebraic structure similar to a vertex algebra, with a deformed translation covariance axiom. We study the structure theory of $\hbar$-vertex algebras, highlighting similarities with the structure theory of vertex algebras. We prove results analogous to Goddard's Uniqueness Theorem, Reconstruction Theorem, Borcherds Identity and OPE Expansion Formula. We also introduce the related notions of a $\hbar$-Lie conformal algebra and of a $\hbar$-Poisson vertex algebra. The main example of $\hbar$-vertex algebras are vertex algebras with deformed vertex operators $Y_\hbar(a,z)=(1+\hbar z)^{\Delta_a}Y(a,z)$, where $\Delta_a$ is the eigenvalue of a Hamiltonian operator $H$. We simplify the construction of the Zhu algebra using the formalism of $\hbar$-vertex algebras. As a further application of the theory developed in the first part of the paper, we discuss the chiralization of classical star-products. We compute explicit formulae for the chiralization of a class of star-products, including the Moyal-Weyl and the Gutt star-products. Putting $\hbar=0$, these formulae yield explicit formulae for deformation quantizations of a class of Poisson vertex algebras., Comment: Typos corrected, Section 3.5 added

We present a study of the soft transverse optic phonon mode in SnTe in comparison to the corresponding mode in PbTe using inelastic neutron scattering and ab-initio lattice dynamical calculations. In contrast to previous reports our calculations predict that the soft mode in SnTe features a strongly asymmetric spectral weight distribution qualitatively similar to that found in PbTe. Experimentally, we find that the overall width in energy of the phonon peaks is comparable in our neutron scattering spectra for SnTe and PbTe. We observe the well-known double-peak-like signature of the TO mode in PbTe even down to $T$ = 5 K questioning its proposed origin purely based on phonon-phonon scattering. The proximity to the incipient ferroelectric transition in PbTe likely plays an important role not included in current models.

Electron-phonon coupling, i.e., the scattering of lattice vibrations by electrons and vice versa, is ubiquitous in solids and can lead to emergent ground states such as superconductivity and charge-density wave order. Strong coupling of phonons to electrons near the Fermi surface, which reduces the phonon lifetimes and broadens the phonon peaks in scattering experiments, is often associated with Fermi surface nesting. Here, we show that strong phonon broadening can occur in the absence of both Fermi surface nesting and lattice anharmonicity, if electron-phonon coupling is strongly enhanced for specific values of electron-momentum, k. We use inelastic neutron scattering, soft x-ray angle-resolved photoemission spectroscopy measurements and ab-initio lattice dynamical and electronic band structure calculations to demonstrate this scenario in the highly anisotropic tetragonal electron-phonon superconductor YNi$_2$B$_2$C. This new scenario likely applies to a wide range of compounds.

Concurrent strategies based on event structures are examined from the viewpoint of 'may' and 'must' testing in traditional process calculi. In their pure form concurrent strategies fail to expose the deadlocks and divergences that can arise in their composition. This motivates an extension of the bicategory of concurrent strategies to treat the 'may' and 'must' behaviour of strategies under testing. One extension adjoins neutral moves to strategies but in so doing loses identities w.r.t. composition. This in turn motivates another extension in which concurrent strategies are accompanied by stopping configurations; the ensuing stopping strategies inherit the structure of a bicategory from that of strategies. The technical developments converge in providing characterisations of the 'may' and 'must' equivalences and preorders on strategies.

We propose a text classification tool based on support vector machines for the assessment of organizational leadership styles, as appearing to Twitter users. We collected Twitter data over 51 days, related to the first 30 Italian organizations in the 2015 ranking of Forbes Global 2000-out of which we selected the five with the most relevant volumes of tweets. We analyzed the communication of the company leaders, together with the dialogue among the stakeholders of each company, to understand the association with perceived leadership styles and dimensions. To assess leadership profiles, we referred to the 10-factor model developed by Barchiesi and La Bella in 2007. We maintain the distinctiveness of the approach we propose, as it allows a rapid assessment of the perceived leadership capabilities of an enterprise, as they emerge from its social media interactions. It can also be used to show how companies respond and manage their communication when specific events take place, and to assess their stakeholder's reactions.

Game semantics is a denotational semantics presenting compositionally the computational behaviour of various kinds of effectful programs. One of its celebrated achievement is to have obtained full abstraction results for programming languages with a variety of computational effects, in a single framework. This is known as the semantic cube or Abramsky's cube, which for sequential deterministic programs establishes a correspondence between certain conditions on strategies (''innocence'', ''well-bracketing'', ''visibility'') and the absence of matching computational effects. Outside of the sequential deterministic realm, there are still a wealth of game semantics-based full abstraction results; but they no longer fit in a unified canvas. In particular, Ghica and Murawski's fully abstract model for shared state concurrency (IA) does not have a matching notion of pure parallel program-we say that parallelism and interference (i.e. state plus semaphores) are entangled. In this paper we construct a causal version of Ghica and Murawski's model, also fully abstract for IA. We provide compositional conditions parallel innocence and sequentiality, respectively banning interference and parallelism, and leading to four full abstraction results. To our knowledge, this is the first extension of Abramsky's semantic cube programme beyond the sequential deterministic world.

Game semantics has proven to be a robust method to give compositional semantics for a variety of higher-order programming languages. However, due to the complexity of most game models, game semantics has remained unapproachable for non-experts. In this paper, we aim at making game semantics more accessible by viewing it as a syntactic translation into a session typed pi-calculus, referred to as metalanguage, followed by a semantics interpretation of the metalanguage into a particular game model. The syntactic translation can be defined for a wide range of programming languages without knowledge of the particular game model used. Simple reasoning on the model (soundness, and adequacy) can be done at the level of the metalanguage, escaping tedious technical proofs usually found in game semantics. We call this methodology programming game semantics. We design a metalanguage (PiDiLL) inspired from Differential Linear Logic (DiLL), which is concise but expressive enough to support features required by concurrent game semantics. We then demonstrate our methodology by yielding the first causal, non-angelic and interactive game model of CML, a higher-order call-by-value language with shared memory concurrency. We translate CML into PiDiLL and show that the translation is adequate. We give a causal and non-angelic game semantics model using event structures, which supports a simple semantics interpretation of PiDiLL. Combining both of these results, we obtain the first interactive model of a concurrent language of this expressivity which is adequate with respect to the standard weak bisimulation, and fully abstract for the contextual equivalence on second-order terms. We have implemented a prototype which can explore the generated causal object from a subset of OCaml.

Nematicity is ubiquitous in electronic phases of high-$T_c$ superconductors, particularly in the Fe-based systems. We used inelastic x-ray scattering to extract the temperature-dependent nematic correlation length $\xi$ from the anomalous softening of acoustic phonon modes in FeSe, underdoped Ba(Fe$_{0.97}$Co$_{0.03}$)$_2$As$_2$ and optimally doped Ba(Fe$_{0.94}$Co$_{0.06}$)$_2$As$_2$. In all cases, we find that $\xi$ is well described by a power law $(T-T_0)^{-1/2}$ extending over a wide temperature range. We attributed this mean-field behavior and the extended fluctuation regime to a sizable nemato-elastic coupling, which may be detrimental to superconductivity.

We show how the categorical logic of untyped, simply typed and dependently typed lambda calculus can be structured around the notion of category with family (cwf). To this end we introduce subcategories of simply typed cwfs (scwfs), where types do not depend on variables, and unityped cwfs (ucwfs), where there is only one type. We prove several equivalence and biequivalence theorems between cwf-based notions and basic notions of categorical logic, such as cartesian operads, Lawvere theories, categories with finite products and limits, cartesian closed categories, and locally cartesian closed categories. Some of these theorems depend on the restrictions of contextuality (in the sense of Cartmell) or democracy (used by Clairambault and Dybjer for their biequivalence theorems). Some theorems are equivalences between notions with strict preservation of chosen structure. Others are biequivalences between notions where properties are only preserved up to isomorphism. In addition to this we discuss various constructions of initial ucwfs, scwfs, and cwfs with extra structure.

Nematicity is ubiquitous in electronic phases of high-$T_c$ superconductors, particularly in the Fe-based systems. While several experiments have probed nematic fluctuations, they have been restricted to uniform or momentum averaged fluctuations. Here, we investigate the behavior of finite-momentum nematic fluctuations by utilizing the anomalous softening of acoustic phonon modes in optimally doped Ba(Fe$_{0.94}$Co$_{0.06}$)$_2$As$_2$. We determine the nematic correlation length and find that it sharply changes its $T$-dependence at $T_c$, revealing a strong connection between nematicity and superconductivity.

According to standard theory the magnetoresistance magnitude in ferromagnetic manganites crucially depends on the electron-phonon coupling strength. We showed that in La0.7Sr0.3MnO3 the phonon renormalization is strong, despite its relatively small magnetoresistance. Here, we report results of a similar inelastic neutron scattering investigation of a closely related compound, La0.8Sr0.2MnO3, where the magnetoresistance is enhanced. We find similar phonon renormalization and dynamic CE-type polaron correlations as in La0.7Sr0.3MnO3. However, quantitative comparison of the results for the two samples shows that only polaron lifetime is well correlated with the strength of the CMR., Comment: 5 figures

The heavy-fermion compound CeCu$_{6-x}$Au$_x$ has become a model system for unconventional magnetic quantum criticality. For small Au concentrations $0 \leq x < 0.16$, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature $T_{s}$ with $T_{s} \rightarrow 0$ for $x \approx 0.15$. Antiferromagnetic order sets in close to $x \approx 0.1$. To shed light on the interplay between quantum critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with $0 \leq x\leq 0.3$. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between $x\approx 0.1$ and $0.15$. The application of hydrostatic and chemical pressure allows to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion., Comment: 5 pages, 3 figures

FeCrAs displays an unusual electrical response that is neither metallic in character nor divergent at low temperatures, as expected for an insulating response, and therefore it has been termed a "nonmetal-metal". We carried out neutron scattering experiments on powder and single crystal samples to study the magnetic dynamics and critical fluctuations in FeCrAs. Magnetic neutron diffraction measurements find Cr3+ magnetic order setting in at 115 K with the mean-field critical exponent. Neutron spectroscopy, however, observes gapless stiff magnetic fluctuations emanating from magnetic positions with propagation wave vector q_0=(1/3,1/3), which persists up to at least 80 meV. The magnetism in FeCrAs therefore displays a response which resembles that of itinerant magnets at high energy transfers, such as chromium alloys. We suggest that the presence of stiff high-energy spin fluctuations is the origin of the unusual temperature dependence of the resistivity., Comment: 7 pages, 5 figures

The origin of the effect of colossal magneto-resistance (CMR) remains still unexplained. In this work we revisit the spin dynamics of the pseudo-cubic La1-xSrxMnO3 along the Mn-O-Mn bond direction at four x doping values (x < 0.5) and various temperatures and report a new lattice dynamics study at x0=0.2, representative of the optimal doping for CMR. We propose an interpretation of the spin dynamics in terms of orbital polarons. This picture is supported by the observation of a discrete magnetic energy spectrum Enmag (q) characteristic of the internal excitations of "orbital polarons" defined by Mn3+ neighbors surrounding a Mn4+ center with a hole. Because of its hopping, the hole mixes up dynamically all the possible orbital configurations of its surrounding Mn3+ sites with degenerate energies. The Enmag values indicate a lift of orbital degeneracy by phonon excitations. The number n varies with the spatial dimension D of the polaron and the q-range determines its size. At x=0.125 and x=0.3 the spectrum reveals 2D polarons coupled by exchange and 3D "free" polarons respectively, with sizes l=1.67a < 2a in all bond directions. At x0=0.2, the spin and the lattice dynamics provide evidence for chains of orbital polarons of size l=2a with a periodic distribution over ~ 3a and an interaction energy ~ 3 meV. At T < Tc the charges propagate together with the longitudinal acoustic phonons along the chains enhancing their ferromagnetic character. The phase separation between metallic and ferromagnetic chains in a non-metallic matrix may be crucial for CMR.

Electron-phonon interaction in copper oxide superconductors is still enigmatic. Strong coupling for certain optic phonons is now well established experimentally, but theoretical understanding is challenging. Scattering of electrons near the Fermi surface by the longitudinal acoustic (LA) phonons is expected from basic theory because these phonons modulate electron density. We used inelastic neutron scattering on a large single crystal sample of optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ to show that low-energy LA phonons could couple to electronic density fluctuations only at small phonon wavevectors, which naturally limits any interaction to forward scattering. Such scattering should not be pairbreaking in the case of the d-wave gap. We also found that previously the reported low energy phonon spectral weight half-way to the zone boundary is consistent with conventional lattice dynamics and does not reflect an incipient charge density wave., Comment: Updated Oct. 2019 to include new measurements and additional discussion. 7 pages, 4 figures, Supplementary included: 6 pages, 5 figures

Global sensitivity analysis is a set of methods aiming at quantifying the contribution of an uncertain input parameter of the model (or combination of parameters) on the variability of the response. We consider here the estimation of the Sobol indices of order 1 which are commonly-used indicators based on a decomposition of the output's variance. In a deterministic framework, when the same inputs always give the same outputs, these indices are usually estimated by replicated simulations of the model. In a stochastic framework, when the response given a set of input parameters is not unique due to randomness in the model, metamodels are often used to approximate the mean and dispersion of the response by deterministic functions. We propose a new non-parametric estimator without the need of defining a metamodel to estimate the Sobol indices of order 1. The estimator is based on warped wavelets and is adaptive in the regularity of the model. The convergence of the mean square error to zero, when the number of simulations of the model tend to infinity, is computed and an elbow effect is shown, depending on the regularity of the model. Applications in Epidemiology are carried to illustrate the use of non-parametric estimators.

Intermediate valence compounds containing rare earth or actinide ions are archetypal systems for the investigation of strong electron correlations. Their effective electron masses of 10 to 50 times the free electron mass result from a hybridization of the highly localized $f$-electrons with the more itinerant $d$-electrons, which is strong enough that their properties are dominated by on-site electron correlations. To a remarkable degree, this can be modeled by the Anderson Impurity Model, even though the $f$-electrons are situated on a periodic lattice. However, in recent years, there has been increasing evidence that the dynamic magnetic susceptibility of intermediate valence compounds is not purely local, but shows variations across the Brillouin zone that have been ascribed to $f$-band coherence. So far, this has been based on simplified qualitative models. In this article, we present a quantitative comparison of inelastic neutron scattering from a single crystal of CePd$_3$, measured in four-dimensional (Q,$\omega$)-space, with ab initio calculations, which are in excellent agreement on an absolute scale. Our results establish that the Q-dependence of the scattering is caused by particle-hole excitations within $f$-$d$ hybridized bands that grow in coherence with decreasing temperature., Comment: 8 page article with 6 figures, 4 page supplementary information with 8 figures