Local search for stable marriage problems

The stable marriage (SM) problem has a wide variety of practical applications, ranging from matching resident doctors to hospitals, to matching students to schools, or more generally to any two-sided market. In the classical formulation, n men and n women express their preferences (via a strict total order) over the members of the other sex. Solving a SM problem means finding a stable marriage where stability is an envy-free notion: no man and woman who are not married to each other would both prefer each other to their partners or to being single. We consider both the classical stable marriage problem and one of its useful variations (denoted SMTI) where the men and women express their preferences in the form of an incomplete preference list with ties over a subset of the members of the other sex. Matchings are permitted only with people who appear in these lists, an we try to find a stable matching that marries as many people as possible. Whilst the SM problem is polynomial to solve, the SMTI problem is NP-hard. We propose to tackle both problems via a local search approach, which exploits properties of the problems to reduce the size of the neighborhood and to make local moves efficiently. We evaluate empirically our algorithm for SM problems by measuring its runtime behaviour and its ability to sample the lattice of all possible stable marriages. We evaluate our algorithm for SMTI problems in terms of both its runtime behaviour and its ability to find a maximum cardinality stable marriage.For SM problems, the number of steps of our algorithm grows only as O(nlog(n)), and that it samples very well the set of all stable marriages. It is thus a fair and efficient approach to generate stable marriages.Furthermore, our approach for SMTI problems is able to solve large problems, quickly returning stable matchings of large and often optimal size despite the NP-hardness of this problem.Comment: 12 pages, Proc. COMSOC 2010 (Third International Workshop on Computational Social Choice

Validity and reliability of the Structured Clinical Interview for Depersonalization-Derealization Spectrum (SCI-DER).

This study evaluates the validity and reliability of a new instrument developed to assess symptoms of depresonalization: the Structured Clinical Interview for the Depersonalization-Derealization Spectrum (SCI-DER). The instrument is based on a spectrum model that emphasizes soft-signs, sub-threshold syndromes as well as clinical and subsyndromal manifestations. Items of the interview include, in addition to DSM-IV criteria for depersonalization, a number of features derived from clinical experience and from a review of phenomenological descriptions. Study participants included 258 consecutive patients with mood and anxiety disorders, 16.7% bipolar I disorder, 18.6% bipolar II disorder, 32.9% major depression, 22.1% panic disorder, 4.7% obsessive compulsive disorder, and 1.5% generalized anxiety disorder; 2.7% patients were also diagnosed with depersonalization disorder. A comparison group of 42 unselected controls was enrolled at the same site. The SCI-DER showed excellent reliability and good concurrent validity with the Dissociative Experiences Scale. It significantly discriminated subjects with any diagnosis of mood and anxiety disorders from controls and subjects with depersonalization disorder from controls. The hypothesized structure of the instrument was confirmed empirically

Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature

The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied within the context of a finite-temperature Green's function theory. The equilibrium state and the field dependence of the magnon energy gap $E_0$ are calculated for static magnetic field $H$ applied in plane along an easy or a hard axis. In the latter case, the in-plane reorientation of the magnetization is shown to be continuous at T=0, in agreement with free spin wave theory, and discontinuous at finite temperature $T>0$, in contrast with the prediction of mean field theory. The discontinuity in the orientation angle creates a jump in the magnon energy gap, and it is the reason why, for $T>0$, the energy does not go to zero at the reorientation field. Above the Curie temperature $T_C$, the magnon energy gap $E_0(H)$ vanishes for H=0 both in the easy and in the hard case. As $H$ is increased, the gap is found to increase almost linearly with $H$, but with different slopes depending on the field orientation. In particular, the slope is smaller when $H$ is along the hard axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist well above $T_C$ ($T \approx 1.2 T_C$).Comment: Final version accepted for publication in Physical Review B (with three figures

Phase transitions in simple and not so simple binary fluids

Compared to pure fluids, binary mixtures display a very diverse phase behavior, which depends sensitively on the parameters of the microscopic potential. Here we investigate the phase diagrams of simple model mixtures by use of a microscopic implementation of the renormalization group technique. First, we consider a symmetric mixture with attractive interactions, possibly relevant for describing fluids of molecules with internal degrees of freedom. Despite the simplicity of the model, slightly tuning the strength of the interactions between unlike species drastically changes the topology of the phase boundary, forcing or inhibiting demixing, and brings about several interesting features such as double critical points, tricritical points, and coexistence domains enclosing `islands' of homogeneous, mixed fluid. Homogeneous phase separation in mixtures can be driven also by purely repulsive interactions. As an example, we consider a model of soft particles which has been adopted to describe binary polymer solutions. This is shown to display demixing (fluid-fluid) transition at sufficiently high density. The nature and the physical properties of the corresponding phase transition are investigated.Comment: 6 pages + 3 figures, presented at the 5th EPS Liquid Matter Conference, Konstanz, 14-18 September 200

Effect of antiferromagnetic exchange interactions on the Glauber dynamics of one-dimensional Ising models

We study the effect of antiferromagnetic interactions on the single spin-flip Glauber dynamics of two different one-dimensional (1D) Ising models with spin $\pm 1$. The first model is an Ising chain with antiferromagnetic exchange interaction limited to nearest neighbors and subject to an oscillating magnetic field. The system of master equations describing the time evolution of sublattice magnetizations can easily be solved within a linear field approximation and a long time limit. Resonant behavior of the magnetization as a function of temperature (stochastic resonance) is found, at low frequency, only when spins on opposite sublattices are uncompensated owing to different gyromagnetic factors (i.e., in the presence of a ferrimagnetic short range order). The second model is the axial next-nearest neighbor Ising (ANNNI) chain, where an antiferromagnetic exchange between next-nearest neighbors (nnn) is assumed to compete with a nearest-neighbor (nn) exchange interaction of either sign. The long time response of the model to a weak, oscillating magnetic field is investigated in the framework of a decoupling approximation for three-spin correlation functions, which is required to close the system of master equations. The calculation, within such an approximate theoretical scheme, of the dynamic critical exponent z, defined as ${1/\tau} \approx ({1/ {\xi}})^z$ (where \tau is the longest relaxation time and \xi is the correlation length of the chain), suggests that the T=0 single spin-flip Glauber dynamics of the ANNNI chain is in a different universality class than that of the unfrustrated Ising chain.Comment: 5 figures. Phys. Rev. B (accepted July 12, 2007

Dipolar ground state of planar spins on triangular lattices

An infinite triangular lattice of classical dipolar spins is usually considered to have a ferromagnetic ground state. We examine the validity of this statement for finite lattices and in the limit of large lattices. We find that the ground state of rectangular arrays is strongly dependent on size and aspect ratio. Three results emerge that are significant for understanding the ground state properties: i) formation of domain walls is energetically favored for aspect ratios below a critical valu e; ii) the vortex state is always energetically favored in the thermodynamic limit of an infinite number of spins, but nevertheless such a configuration may not be observed even in very large lattices if the aspect ratio is large; iii) finite range approximations to actual dipole sums may not provide the correct ground sta te configuration because the ferromagnetic state is linearly unstable and the domain wall energy is negative for any finite range cutoff.Comment: Several short parts have been rewritten. Accepted for publication as a Rapid Communication in Phys. Rev.

Surface magnetic canting in a ferromagnet

The surface magnetic canting (SMC) of a semi-infinite film with ferromagnetic exchange interaction and competing bulk and surface anisotropies is investigated via a nonlinear mapping formulation of mean-field theory previously developed by our group [L. Trallori et al., Int. J. Mod. Phys. B 10, 1935-1988 (1996)], and extended to the case where an external magnetic field is applied to the system. When the field H is parallel to the film plane, the condition for SMC is found to be the same as that recently reported by Popov and Pappas [Phys. Rev. B 64, 184401 (2001)]. The case of a field H applied perpendicularly to the film plane is also investigated. In both cases, the zero-temperature equilibrium configuration is easily determined by our theoretical approach.Comment: 4 pages, 3 figure

Helmet CPAP to Treat Acute Hypoxemic Respiratory Failure in Patients with COVID-19 : a Management Strategy Proposal

Since the beginning of March 2020, the coronavirus disease 2019 (COVID-19) pandemic has caused more than 13,000 deaths in Europe, almost 54% of which has occurred in Italy. The Italian healthcare system is experiencing a stressful burden, especially in terms of intensive care assistance. In fact, the main clinical manifestation of COVID-19 patients is represented by an acute hypoxic respiratory failure secondary to bilateral pulmonary infiltrates, that in many cases, results in an acute respiratory distress syndrome and requires an invasive ventilator support. A precocious respiratory support with non-invasive ventilation or high flow oxygen should be avoided to limit the droplets' air-dispersion and the healthcare workers' contamination. The application of a continuous positive airway pressure (CPAP) by means of a helmet can represent an effective alternative to recruit diseased alveolar units and improve hypoxemia. It can also limit the room contamination, improve comfort for the patients, and allow for better clinical assistance with long-term tolerability. However, the initiation of a CPAP is not free from pitfalls. It requires a careful titration and monitoring to avoid a delayed intubation. Here, we discuss the rationale and some important considerations about timing, criteria, and monitoring requirements for patients with COVID-19 respiratory failure requiring a CPAP treatment

Static density response of one-dimensional soft bosons across the clustering transition

One-dimensional bosons interacting via a soft-shoulder potential are investigated at zero temperature. The flatness of the potential at short distances introduces a typical length, such that, at relatively high densities and sufficiently strong interactions, clusters are formed, even in the presence of a completely repulsive potential. We evaluate the static density response function of this system across the transition from the liquid to the cluster liquid phases. Such quantity reveals the density modulations induced by a weak periodic external potential, and is maximal at the clustering wavevector. It is known that this response function is proportional to the static structure factor in the classical regime at high temperature, while for this zero-temperature quantum systems, we extract it from the dynamical structure factor evaluated with quantum Monte Carlo methods.Comment: 7 pages, 3 figures. Proceedings of the "Recent Progress in Many-Body Theories" international conference, Pohang, South Korea, 201

A Machine Learning Approach to Monitor the Emergence of Late Intrauterine Growth Restriction

Late intrauterine growth restriction (IUGR) is a fetal pathological condition characterized by chronic hypoxia secondary to placental insufficiency, resulting in an abnormal rate of fetal growth. This pathology has been associated with increased fetal and neonatal morbidity and mortality. In standard clinical practice, late IUGR diagnosis can only be suspected in the third trimester and ultimately confirmed at birth. This study presents a radial basis function support vector machine (RBF-SVM) classification based on quantitative features extracted from fetal heart rate (FHR) signals acquired using routine cardiotocography (CTG) in a population of 160 healthy and 102 late IUGR fetuses. First, the individual performance of each time, frequency, and nonlinear feature was tested. To improve the unsatisfactory results of univariate analysis we firstly adopted a Recursive Feature Elimination approach to select the best subset of FHR-based parameters contributing to the discrimination of healthy vs. late IUGR fetuses. A fine tuning of the RBF-SVM model parameters resulted in a satisfactory classification performance in the training set (accuracy 0.93, sensitivity 0.93, specificity 0.84). Comparable results were obtained when applying the model on a totally independent testing set. This investigation supports the use of a multivariate approach for the in utero identification of late IUGR condition based on quantitative FHR features encompassing different domains. The proposed model allows describing the relationships among features beyond the traditional linear approaches, thus improving the classification performance. This framework has the potential to be proposed as a screening tool for the identification of late IUGR fetuses