Higher Critical Points Research Articles

Transition care in patients with IBD: The pediatric and the adult gastroenterologist's perspective. Results from a national survey

BackgroundTransition is a crucial process in the care of IBD patients, although it remains largely heterogeneous. AimsTo provide an overview of the transition process in Italy and to investigate the perspective of the paediatric and adult physicians. MethodsAn online survey was developed by the Italian Group for Inflammatory Bowel Diseases (IG-IBD) and the Italian Society of Paediatric Gastroenterology, Hepatology and Nutrition (SIGENP). Results104 physicians (62 paediatric and 42 adult gastroenterologists) participated to the survey. The disease status was ranked with the highest priority among the key elements of the transition process. The age of the patient was perceived with a higher priority by paediatric gastroenterologists than by adult ones (p < 0.01). In most cases, the transition was organized through one or more joint meetings. Only less than 25 % of responders reported to involve other professions during transition. The struggle in leaving paediatric setting was perceived as the main obstacle to an effective transition process. Paediatric IBD gastroenterologists ranked the struggle in leaving the paediatric setting and the attending physician as higher critical point than adult gastroenterologists. ConclusionsThe current survey provided a snapshot of the IBD transition process in Italy. The present findings highlight the need to embed transitional care in healthcare policy.

Alternative blends of CO2 for transcritical refrigeration systems. Experimental approach and energy analysis

As a natural refrigerant, Carbon Dioxide (CO2) has been extended in almost all refrigeration fields due to its environmental friendliness, high availability, and high technological development in the main components of the cycle. However, despite the benefits, CO2 is limited to high-capacity applications due to the cost of components and the complex cycle arrangements to overcome the low coefficient of performance (COP) at high ambient temperatures. A simple but effective method to solve this issue involves mixing CO2 with other refrigerants obtaining a new refrigerant mixture with higher critical points, lower working pressures and low global warming potential (GWP). Depending on the mixture percentage, the mixture flammability can be suppressed, and the performance of the refrigeration plant can be increased.Building on this, this work determines theoretically different CO2­based zeotropic blends as an alternative to pure CO2 with the restrictions of non-flammability, GWP below 150 and higher COP than pure CO2. The results suggest two blends of CO2/R1270 and CO2/R32 that have been prepared and energetically tested in a vertical display cooler using pure CO2 as a reference. The results revealed that CO2-blends reduce energy consumption by up to 17.2 % at the ambient temperature of 25 °C and up to 12.2 % at 30 °C. Moreover, the results with CO2-blends were closest to those obtained with pure R1270 and better than R134a under the same operating conditions.

Pairs of nontrivial solutions to concave-linear-convex type elliptic problems

We obtain a pair of nontrivial solutions for a class of concave-linear-convex type elliptic problems that are either critical or subcritical. The solutions we find are neither local minimizers nor of mountain pass type in general. They are higher critical points in the sense that they each have a higher critical group that is nontrivial. This fact is crucial for showing that our solutions are nontrivial. We also prove some intermediate results of independent interest on the localization and homotopy invariance of critical groups of functionals involving critical Sobolev exponents.

Liquid network connectivity regulates the stability and composition of biomolecular condensates with many components

One of the key mechanisms used by cells to control the spatiotemporal organization of their many components is the formation and dissolution of biomolecular condensates through liquid-liquid phase separation (LLPS). Using a minimal coarse-grained model that allows us to simulate thousands of interacting multivalent proteins, we investigate the physical parameters dictating the stability and composition of multicomponent biomolecular condensates. We demonstrate that the molecular connectivity of the condensed-liquid network-i.e., the number of weak attractive protein-protein interactions per unit of volume-determines the stability (e.g., in temperature, pH, salt concentration) of multicomponent condensates, where stability is positively correlated with connectivity. While the connectivity of scaffolds (biomolecules essential for LLPS) dominates the phase landscape, introduction of clients (species recruited via scaffold-client interactions) fine-tunes it by transforming the scaffold-scaffold bond network. Whereas low-valency clients that compete for scaffold-scaffold binding sites decrease connectivity and stability, those that bind to alternate scaffold sites not required for LLPS or that have higher-than-scaffold valencies form additional scaffold-client-scaffold bridges increasing stability. Proteins that establish more connections (via increased valencies, promiscuous binding, and topologies that enable multivalent interactions) support the stability of and are enriched within multicomponent condensates. Importantly, proteins that increase the connectivity of multicomponent condensates have higher critical points as pure systems or, if pure LLPS is unfeasible, as binary scaffold-client mixtures. Hence, critical points of accessible systems (i.e., with just a few components) might serve as a unified thermodynamic parameter to predict the composition of multicomponent condensates.

Direct measurement of the upper critical field in cuprate superconductors.

In the quest to increase the critical temperature Tc of cuprate superconductors, it is essential to identify the factors that limit the strength of superconductivity. The upper critical field Hc2 is a fundamental measure of that strength, yet there is no agreement on its magnitude and doping dependence in cuprate superconductors. Here we show that the thermal conductivity can be used to directly detect Hc2 in the cuprates YBa2Cu3Oy, YBa2Cu4O8 and Tl2Ba2CuO6+δ, allowing us to map out Hc2 across the doping phase diagram. It exhibits two peaks, each located at a critical point where the Fermi surface of YBa2Cu3Oy is known to undergo a transformation. Below the higher critical point, the condensation energy, obtained directly from Hc2, suffers a sudden 20-fold collapse. This reveals that phase competition—associated with Fermi-surface reconstruction and charge-density-wave order—is a key limiting factor in the superconductivity of cuprates.

Dicke–Hepp–Lieb superradiant phase transition and independent modes model in quantum optomechanics

We show that in the strong coupling linear regime, the dispersive opto-mechanical Hamiltonian system can undergo a Dicke–Hepp–Lieb superradiant phase transition with two critical points. The higher critical point is the usual second order Dicke superradiant phase transition while the lower critical point is a new effect showing similarity to the usual Dicke superradiance. We also show that the mechanical mode near its quantum ground state completely decouples from the optical mode and the optical mode shows similarity to the Bogoluibov like excitations.

Comparative study of tetragonal Cu 2In 7Se 11.5 and trigonal CuIn 5Se 8 by spectroscopic ellipsometry

A comparative study of chalcopyrite-related Cu 2In 7Se 11.5 and CuIn 5Se 8 crystals by spectroscopic ellipsometry is presented. Their complex dielectric function ɛ( ω) = ɛ 1( ω) + iɛ 2( ω) has been determined in the 0.8–4.7 eV photon energy range. The spectral dependence of ɛ 1( ω) and ɛ 2( ω) as well as the complex refractive index, the absorption coefficient and the normal-incidence reflectivity for tetragonal Cu 2In 7Se 11.5 and trigonal CuIn 5Se 8 crystals have been modelled using the Adachi's model for interband transitions. The results are in a good agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap ( E 0) and higher critical points ( E 1 A , E 1 B ), have been determined using the simulated annealing algorithm. The results show that the tetragonal CuIn 3Se 5, the tetragonal Cu 2In 7Se 11.5 and the trigonal CuIn 5Se 8 crystals belong to different phases of the Cu 4In 2 n Se 2+3 n system, n = 6, n = 7 and n = 10, respectively.

Ab-Initio Studies of Electronic and Spectroscopic Properties of MgO, ZnO and CdO

We present ab-initio calculations of excited-state properties within single-particle and two-particle approaches in comparison with corresponding experimental results. For the theoretical treatment of the electronic structure, we compute eigenvalues and eigenfunctions by using a spatially nonlocal exchange-correlation potential. From this starting point, quasiparticle energies within the fully frequency-dependent G(0)W(0) approximation are obtained. By solving the Bethe-Salpeter equation, we evaluate optical properties, including the electron-hole attraction and the local-field effects. The results are compared with experimental spectra from soft X-ray emission, as well as from X-ray photoelectron spectroscopy or ellipsometry measurements. In more detail, we compute the valence-band densities of states, bound excitons, and the dielectric function. For the latter, we discuss both the absorption edge and higher critical points.

Analysis of the optical properties of Cu(In1−xGax)3Se5 crystals

Analysis of the optical properties of bulk Cu(In1−xGax)3Se5 mixed crystals synthesized from the elements as a function of the Ga content is presented. Measurements of the complex dielectric function ε(ω)=ε1(ω)+iε2(ω) were performed at room temperature in the photon energy range of 0.8–4.7 eV using a variable angle of incidence ellipsometer. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived. The structure observed in the dielectric functions attributed to the interband transitions E0, E1A, and E1B has been modeled using a modification of the Adachi’s model. The results are in excellent agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap and higher critical points, have been determined using the simulated annealing algorithm. The values of E0 and E1A are found to increase linearly with the increasing Ga content.

Quantum confinement in layer-by-layer deposited colloidal HgTe nanocrystals determined by spectroscopic ellipsometry

We report spectroscopic ellipsometry studies in the energy range of 0.5–5 eV on samples of 1–10 bilayers of polymer and HgTe nanocrystals, which exhibit strong transitions at higher critical points in the dispersion relation. We show that the dispersion relation for nanocrystals can be modelled with the same concepts for critical points as used in semiconductor bulk optics. We find an energy shift of up to 0.4 eV of the critical points to higher energies compared to the HgTe bulk properties, caused by quantum confinement in the nanocrystals, which increases with decreasing nanocrystal size.

Dielectric functions and fundamental band gaps of Cu2In4Se7, CuGa3Se5 and CuGa5Se8 crystals

Room temperature pseudodielectric function spectra ε(ω) = ε1 (ω) + iε2(ω) of the ordered defects compounds Cu2In4Se7, CuGa3Se5 and CuGa5Se8 have been measured by spectroscopic ellipsometry. The values of refractive index n and extinction coefficient k are given. The structures observed in ε(ω) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E0) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGaxSey samples is deduced.

Effect of quantum confinement on higher transitions in HgTe nanocrystals

Spectroscopic ellipsometry measurements on 1–10 bilayers of HgTe nanocrystals and polymer were performed in the spectral range from 0.5to5eV. The experiments show that the band model, respectively, band energy shifts due to quantization, can be applied onto nanocrystals with as few as five unit cells in diameter. These nanocrystals exhibit strong transitions at higher critical points. The critical point energies shift up to 0.4eV. It turns out that transitions between bands which are closer to the Fermi energy and have a smaller carrier mass are more strongly affected by quantum confinement.

Resonant Raman spectroscopy on InN

AbstractThe novel use of resonant Raman spectroscopy to elucidate the band gap of InN is illustrated in a study of MBE‐grown films. This technique can distinguish between electronic transitions related to the InN from transitions related to defects and impurities that are so typical for current InN material. Using excitation energies from 1.49 eV (830 nm) to 2.54 eV (488 nm), we identify a critical point in the InN band structure within ≈200–300 meV below 1.5 eV. The origin of this critical point, whether band gap or higher critical point, is discussed. Furthermore, Raman results are presented on the temperature dependence of the InN phonons. Analysis of the data provides information on phonon lifetimes and decay mechanisms, important to assess whether hot phonon effects need to be considered in future InN devices. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Raman spectroscopy study of InN

We report on the Raman analysis of InN films grown by molecular beam epitaxy (MBE), RF sputtering and remote-plasma enhanced chemical vapor deposition (RPE-CVD). Varying the excitation wavelength, information on the homogeneity of the InN films and the free carrier concentration is extracted. The use of UV Raman spectroscopy to probe excess nitrogen in the InN films via a Raman band located around 2300 cm −1 is illustrated. RF sputtered InN was found to contain significantly more excess nitrogen than MBE and RPE-CVD grown InN. The use of resonant Raman scattering spectroscopy to contribute information to the current controversy of the InN band gap is proposed and first results are presented. Resonant Raman scattering under 1.49 eV excitation suggests the presence of a critical point in the InN band structure within 200–300 meV of this laser excitation energy. Further investigations will be needed to clarify whether this is the band gap or a higher critical point in the band structure.

Specific features of depolarized and polarized light scattering in a solution with a layering isolated region

Intensities of depolarized and polarized light scattering in guaiacol-glycerin solutions with layering isolated regions are measured. It is shown that (a) the depolarized scattering intensity is the same above the higher critical point (HCP) and below the lower critical point (LCP), and (b) the polarized scattering intensity below LCP is higher, the higher the HCP. An empirical formula is offered to describe the polarized scattered light intensity. No increase in the single depolarized scattering intensity is found approaching LCP and HCP.

Optical Properties of InS under High Pressure

AbstractPressure effects are studied on the fundamental indirect gap (Eg), direct gap (B0), and next higher critical point (B) in InS single crystals by using a diamond‐anvil cell for the first time. A synchronized decrease of their energies is observed with pressure increasing up to 2 GPa. This unusual behavior is inferred partly due to a softening of InIn bond under pressure.