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28,765 result(s) for "Critical point"
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HACCP : a food industry briefing
\"Readers of this accessible book - now in a revised and updated new edition - are taken on a conceptual journey which passes every milestone and important feature of the HACCP landscape at a pace which is comfortable and productive. The information and ideas contained in the book will enable food industry managers and executives to take their new-found knowledge into the workplace for use in the development and implementation of HACCP systems appropriate for their products and manufacturing processes.The material is structured so that the reader can quickly assimilate the essentials of the topic. Clearly presented, this HACCP briefing includes checklists, bullet points, flow charts, schematic diagrams for quick reference, and at the start of each section the authors have provided useful key points summary boxes. HACCP: a Food Industry Briefing is an introductory-level text for readers who are unfamiliar with the subject either because they have never come across it or because they need to be reminded. The book will also make a valuable addition to material used in staff training and is an excellent core text for HACCP courses\"-- Provided by publisher.
Enhancement and maximum in the isobaric specific-heat capacity measurements of deeply supercooled water using ultrafast calorimetry
Knowledge of the temperature dependence of the isobaric specific heat (Cp) upon deep supercooling can give insights regarding the anomalous properties of water. If a maximum in Cp exists at a specific temperature, as in the isothermal compressibility, it would further validate the liquid–liquid critical point model that can explain the anomalous increase in thermodynamic response functions. The challenge is that the relevant temperature range falls in the region where ice crystallization becomes rapid, which has previously excluded experiments. Here, we have utilized a methodology of ultrafast calorimetry by determining the temperature jump from femtosecond X-ray pulses after heating with an infrared laser pulse and with a sufficiently long time delay between the pulses to allow measurements at constant pressure. Evaporative cooling of ∼15-μm diameter droplets in vacuum enabled us to reach a temperature down to ∼228 K with a small fraction of the droplets remaining unfrozen. We observed a sharp increase in Cp, from 88 J/mol/K at 244 K to about 218 J/mol/K at 229 K where a maximum is seen. The Cp maximum is at a similar temperature as the maxima of the isothermal compressibility and correlation length. From the Cp measurement, we estimated the excess entropy and self-diffusion coefficient of water and these properties decrease rapidly below 235 K.
Liquid water is a dynamic polydisperse branched polymer
We developed the RexPoN force field for water based entirely on quantum mechanics. It predicts the properties of water extremely accurately, with T melt = 273.3 K (273.15 K) and properties at 298 K: ΔHvap = 10.36 kcal/mol (10.52), density = 0.9965 g/cm³ (0.9965), entropy = 68.4 J/mol/K (69.9), and dielectric constant = 76.1 (78.4), where experimental values are in parentheses. Upon heating from 0.0 K (ice) to 273.0 K (still ice), the average number of strong hydrogen bonds (SHBs, rOO ≤ 2.93 Å) decreases from 4.0 to 3.3, but upon melting at 273.5 K, the number of SHBs drops suddenly to 2.3, decreasing slowly to 2.1 at 298 K and 1.6 at 400 K. The lifetime of the SHBs is 90.3 fs at 298 K, increasing monotonically for lower temperature. These SHBs connect to form multibranched polymer chains (151 H₂O per chain at 298 K), where branch points have 3 SHBs and termination points have 1 SHB. This dynamic fluctuating branched polymer view of water provides a dramatically modified paradigm for understanding the properties of water. It may explain the 20-nm angular correlation lengths at 298 K and the critical point at 227 K in supercooled water. Indeed, the 15% jump in the SHB lifetime at 227 K suggests that the supercooled critical point may correspond to a phase transition temperature of the dynamic polymer structure. This paradigm for water could have a significant impact on the properties for protein, DNA, and other materials in aqueous media.
Pure nematic quantum critical point accompanied by a superconducting dome
When a symmetry-breaking phase of matter is suppressed to a quantum critical point (QCP) at absolute zero, quantum-mechanical fluctuations proliferate. Such fluctuations can lead to unconventional superconductivity, as evidenced by the superconducting domes often found near magnetic QCPs in correlated materials. Experimentally, however, it remains much less clear whether the superconductivity can be promoted around QCPs of the electronic nematic phase, characterized by rotational symmetry breaking. Here, we demonstrate from systematic elastoresistivity measurements that nonmagnetic FeSe1−x Teₓ exhibits an electronic nematic QCP showing diverging nematic susceptibility. This finding establishes two nematic QCPs in FeSe-based superconductors with contrasting accompanying phase diagrams. In FeSe1−x Teₓ, a superconducting dome is centered at the QCP, whereas FeSe1−x Sₓ shows no QCP-associated enhancement of superconductivity. We find that this difference is related to the relative strength of nematic and spin fluctuations. Our results in FeSe1−x Teₓ present the unprecedented case in support of the superconducting dome being associated with the QCP of pure electronic nematic order, which does not intertwine with any other long-range orders.
Fermionic quantum critical point of spinless fermions on a honeycomb lattice
Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of the Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recent discovery (Huffman and Chandrasekharan 2014 Phys. Rev. B 89 111101) of the absence of the fermion sign problem in this model, we study the fermionic quantum critical point using the continuous-time quantum Monte Carlo method with a worm-sampling technique. We estimate the transition point with the critical exponents and . Compatible results for the transition point are also obtained with infinite projected entangled-pair states.
THE COMPLEXITY OF SPHERICAL p-SPIN MODELS—A SECOND MOMENT APPROACH
Recently, Auffinger, Ben Arous and Černý initiated the study of critical points of the Hamiltonian in the spherical pure p-spin spin glass model, and established connections between those and several notions from the physics literature. Denoting the number of critical values less than Nu by CrtN(u), they computed the asymptotics of $\\frac{1}{\\mathrm{N}} \\ \\mathrm{log}\\left(\\mathrm{\\mathbb{E}}\\mathrm{C}\\mathrm{r}{\\mathrm{t}}_{\\mathrm{N}}\\right(\\mathrm{u}\\left)\\right)$, as N, the dimension of the sphere, goes to ∞. We compute the asymptotics of the corresponding second moment and show that, for p ≥ 3 and sufficiently negative u, it matches the first moment: 𝔼{(CrtN(u))2}/(𝔼{CrtN(u)})2 → 1. As an immediate consequence we obtain that CrtN(u)/𝔼{CrtN(u)} → 1, in L2, and thus in probability. For any u for which 𝔼CrtN(u) does not tend to 0 we prove that the moments match on an exponential scale.
Critical point for Bose–Einstein condensation of excitons in graphite
An exciton is an electron–hole pair bound by attractive Coulomb interaction. Short-lived excitons have been detected by a variety of experimental probes in numerous contexts. An excitonic insulator, a collective state of such excitons, has been more elusive. Here, thanks to Nernst measurements in pulsed magnetic fields, we show that in graphite there is a critical temperature (T = 9.2 K) and a critical magnetic field (B = 47 T) for Bose–Einstein condensation of excitons. At this critical field, hole and electron Landau subbands simultaneously cross the Fermi level and allow exciton formation. By quantifying the effective mass and the spatial separation of the excitons in the basal plane, we show that the degeneracy temperature of the excitonic fluid corresponds to this critical temperature. This identification would explain why the field-induced transition observed in graphite is not a universal feature of three-dimensional electron systems pushed beyond the quantum limit.
Solid–liquid critical behavior of water in nanopores
Nanoconfined liquid water can transform into low-dimensional ices whose crystalline structures are dissimilar to any bulk ices and whose melting point may significantly rise with reducing the pore size, as revealed by computer simulation and confirmed by experiment. One of the intriguing, and as yet unresolved, questions concerns the observation that the liquid water may transform into a low-dimensional ice either via a first-order phase change or without any discontinuity in thermodynamic and dynamic properties, which suggests the existence of solid–liquid critical points in this class of nanoconfined systems. Here we explore the phase behavior of a model of water in carbon nanotubes in the temperature–pressure–diameter space by molecular dynamics simulation and provide unambiguous evidence to support solid–liquid critical phenomena of nanoconfined water. Solid–liquid first-order phase boundaries are determined by tracing spontaneous phase separation at various temperatures. All of the boundaries eventually cease to exist at the critical points and there appear loci of response function maxima, or the Widom lines, extending to the supercritical region. The finite-size scaling analysis of the density distribution supports the presence of both first-order and continuous phase changes between solid and liquid. At around the Widom line, there are microscopic domains of two phases, and continuous solid–liquid phase changes occur in such a way that the domains of one phase grow and those of the other evanesce as the thermodynamic state departs from the Widom line.
Evaluating the Anisotropy of Drilling Mechanical Characteristics of Rock in the Process of Digital Drilling
The engineering behaviour of rock is strongly associated with the anisotropy, which exists at different scales for construction safety and evaluation of rock properties. It is also well known that the anisotropy of the drilling mechanical characteristics in the rock cutting process has an essential effect on the drilling efficiency and cost. For this purpose, an effort was made to characterize the anisotropy of the drilling mechanical characteristics of rocks in the rock drilling process. The drilling strength and specific energy at the cutting point are considered to characterize the drilling process in three different directions according to the drilling response model. A drilling characteristic-based index is proposed to evaluate the anisotropy of rock. Drilling tests were conducted in three directions for six types of rock to study the anisotropy variation along the borehole depth. The anisotropy evolution result along the borehole suggested that this critical point is identified as the cutting point, dividing the drilling process into two stages of cutting and frictional contact. The cutting point also shows anisotropic features. The anisotropic ranking of tested rocks was obtained. Based on how the drilling parameters depend on the unconfined compressive strength, the reliability of the proposed anisotropy index is examined by comparison with the strength anisotropy index. The comparative result demonstrates that the proposed method can provide a reliable determination for rock anisotropy by using the drilling strength. The work performed in this paper provides a very useful approach for evaluating the anisotropy of rock and provides a good understanding of the drilling mechanical characteristics in rock drilling.HighlightsThe anisotropy of the drilling mechanical characteristics of rocks is characterized in the rock drilling process.The drilling strength and specific energy at the cutting point are considered to characterize the drilling process in three different directions.A drilling characteristic-based index is proposed to evaluate the anisotropy of rock.Drilling tests are conducted in three directions for six types of rock to study the anisotropy variation along the borehole depth.
Enhanced Superconductivity near the Pressure-Tuned Quantum Critical Point of Charge-Density-Wave Order in Cu1-δTe (δ = 0.016)
We have investigated the evolution of CDW states and structural phases in a Cu-deficient Cu1-δTe (δ = 0.016) by employing high-pressure experiments and first-principles calculations. Raman scattering results reveal that the vulcanite structure at ambient pressure starts to change into the Cu-deficient rickardite (r-CuTe) structure from 6.7 GPa, which then becomes fully stabilized above 8.3 GPa. Resistivity data show that TCDW1 (≈333 K) is systematically suppressed under high pressure, reaching zero at 5.9 GPa. In the pressure range of 5.2–8.2 GPa, a sharp resistivity drop due to superconductivity occurs at the onset temperature TC = ~2.0–3.2 K. The maximum TC = 3.2 K achieved at 5.6 GPa is clearly higher than that of CuTe (2.3 K), suggesting the importance of charge fluctuation in the vicinity of CDW suppression. At 7.5 GPa, another resistivity anomaly appears due to the emergence of a second CDW (CDW2) ordering at TCDW2 = ~176 K, which exhibits a gradual increase to ~203 K with pressure increase up to 11.3 GPa. First-principles calculations on the Cu-deficient Cu11Te12 with the r-CuTe structure show that including on-site Coulomb repulsion is essential for incurring an unstable phonon mode relevant for stabilizing the CDW2 order. These results point out the important role of charge fluctuation in optimizing the pressure-induced superconductivity and that of Coulomb interaction in creating the competing CDW order in the Cu-deficient CuTe system.