Phase transition behaviours near the triple point for Pb-free (1 - x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 piezoceramics

NASA Astrophysics Data System (ADS)

Gao, Jinghui; Dai, Ye; Hu, Xinghao; Ke, Xiaoqin; Zhong, Lisheng; Li, Shengtao; Zhang, Lixue; Wang, Yu; Wang, Dong; Wang, Yan; Liu, Yongbin; Xiao, Hu; Ren, Xiaobing

2016-08-01

The reason for the large electromechanical response in Pb-free piezoceramic Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 (BZT-BCT) still remains controversial, and a central issue is whether or not the multi-phase-coexisting point (triple point) in the phase diagram is a thermodynamic tricritical point. In this letter, we study the phase transition behaviour for the ferro-para transitions of BZT-BCT specimens in the vicinity of a triple point. Our results show that latent heat and thermal hysteresis approach zero, while the permittivity peak value is maximized close to the triple-point composition, which suggests that the triple point exhibits nearly tricritical transition behaviours in the BZT-BCT system. Further, the TEM result shows that the domain width is minimized with composition approaching the triple point, which indicates a reduction of the domain wall energy possibly relevant to the tricriticality of the triple point. A sixth-order Landau energy modeling shows that the triple tricritical point provides a free-energy state of near-vanishing polarization anisotropy and thus enhances the piezoelectric response for such a material system.

Nonequilibrium Phase Transitions and a Nonequilibrium Critical Point from Anti-de Sitter Space and Conformal Field Theory Correspondence

NASA Astrophysics Data System (ADS)

Nakamura, Shin

2012-09-01

We find novel phase transitions and critical phenomena that occur only outside the linear-response regime of current-driven nonequilibrium states. We consider the strongly interacting (3+1)-dimensional N=4 large-Nc SU(Nc) supersymmetric Yang-Mills theory with a single flavor of fundamental N=2 hypermultiplet as a microscopic theory. We compute its nonlinear nonballistic quark-charge conductivity by using the AdS/CFT correspondence. We find that the system exhibits a novel nonequilibrium first-order phase transition where the conductivity jumps and the sign of the differential conductivity flips at finite current density. A nonequilibrium critical point is discovered at the end point of the first-order regime. We propose a nonequilibrium steady-state analogue of thermodynamic potential in terms of the gravity-dual theory in order to define the transition point. Nonequilibrium analogues of critical exponents are proposed as well. The critical behavior of the conductivity is numerically confirmed on the basis of these proposals. The present work provides a new example of nonequilibrium phase transitions and nonequilibrium critical points.

Winding numbers of nodal points in Fe-based superconductors

NASA Astrophysics Data System (ADS)

Chichinadze, Dmitry V.; Chubukov, Andrey V.

2018-03-01

We analyze the nodal points in multiorbital Fe-based superconductors from a topological perspective. We consider the s+- gap structure with accidental nodes, and the d -wave gap with nodes along the symmetry directions. In both cases, the nodal points can be moved by varying an external parameter, e.g., a degree of interpocket pairing. Eventually, the nodes merge and annihilate via a Lifshitz-type transition. We discuss the Lifshitz transition in Fe-based superconductors from a topological point of view. We show, both analytically and numerically, that the merging nodal points have winding numbers of opposite sign. This is consistent with the general reasoning that the total winding number is a conserved quantity in the Lifshitz transition.

Spin-flop quasi-first order phase transition and putative tricritical point in Gd3Co

NASA Astrophysics Data System (ADS)

Samatham, S. Shanmukharao; Barua, Soumendu; Suresh, K. G.

2017-12-01

Magnetic nature of Gd3Co is investigated using detailed measurements of temperature and field dependent magnetization. The antiferromagnetic phase is field-instable due to prevailing ferromagnetic exchange correlations above Néel temperature TN ∼ 130K . Below TN , with gradually increasing magnetic fields, the compound undergoes a quasi-first order phase transition from AFM to spin-flop over region and eventually acquires ferromagnetic phase in higher fields. Further the point at which the quasi-first order transition ends and second order transition sets in is the tricritical point, TTCP ∼ 125.6K , HTCP ∼ 4.4kOe .

Ecosystem thresholds, tipping points, and critical transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Munson, Seth M.; Reed, Sasha C.; Peñuelas, Josep

Terrestrial ecosystems in a time of change: thresholds, tipping points, and critical transitions; an organized session at the American Geophysical Union Fall Meeting in New Orleans, Louisiana, USA, December 2017

Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

NASA Technical Reports Server (NTRS)

Obara, C. J.; Holmes, B. J.

1985-01-01

Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.

Lifshitz Transitions, Type-II Dirac and Weyl Fermions, Event Horizon and All That

NASA Astrophysics Data System (ADS)

Volovik, G. E.; Zhang, K.

2017-12-01

The type-II Weyl and type-II Dirac points emerge in semimetals and also in relativistic systems. In particular, the type-II Weyl fermions may emerge behind the event horizon of black holes. In this case the horizon with Painlevé-Gullstrand metric serves as the surface of the Lifshitz transition. This relativistic analogy allows us to simulate the black hole horizon and Hawking radiation using the fermionic superfluid with supercritical velocity, and the Dirac and Weyl semimetals with the interface separating the type-I and type-II states. The difference between such type of the artificial event horizon and that which arises in acoustic metric is discussed. At the Lifshitz transition between type-I and type-II fermions the Dirac lines may also emerge, which are supported by the combined action of topology and symmetry. The type-II Weyl and Dirac points also emerge as the intermediate states of the topological Lifshitz transitions. Different configurations of the Fermi surfaces, involved in such Lifshitz transition, are discussed. In one case the type-II Weyl point connects the Fermi pockets and the Lifshitz transition corresponds to the transfer of the Berry flux between the Fermi pockets. In the other case the type-II Weyl point connects the outer and inner Fermi surfaces. At the Lifshitz transition the Weyl point is released from both Fermi surfaces. They loose their Berry flux, which guarantees the global stability, and without the topological support the inner surface disappears after shrinking to a point at the second Lifshitz transition. These examples reveal the complexity and universality of topological Lifshitz transitions, which originate from the ubiquitous interplay of a variety of topological characters of the momentum-space manifolds. For the interacting electrons, the Lifshitz transitions may lead to the formation of the dispersionless (flat) band with zero energy and singular density of states, which opens the route to room-temperature superconductivity. Originally, the idea of the enhancement of T_c due to flat band has been put forward by the nuclear physics community, and this also demonstrates the close connections between different areas of physics.

Large magnetoresistance dips and perfect spin-valley filter induced by topological phase transitions in silicene

NASA Astrophysics Data System (ADS)

Prarokijjak, Worasak; Soodchomshom, Bumned

2018-04-01

Spin-valley transport and magnetoresistance are investigated in silicene-based N/TB/N/TB/N junction where N and TB are normal silicene and topological barriers. The topological phase transitions in TB's are controlled by electric, exchange fields and circularly polarized light. As a result, we find that by applying electric and exchange fields, four groups of spin-valley currents are perfectly filtered, directly induced by topological phase transitions. Control of currents, carried by single, double and triple channels of spin-valley electrons in silicene junction, may be achievable by adjusting magnitudes of electric, exchange fields and circularly polarized light. We may identify that the key factor behind the spin-valley current filtered at the transition points may be due to zero and non-zero Chern numbers. Electrons that are allowed to transport at the transition points must obey zero-Chern number which is equivalent to zero mass and zero-Berry's curvature, while electrons with non-zero Chern number are perfectly suppressed. Very large magnetoresistance dips are found directly induced by topological phase transition points. Our study also discusses the effect of spin-valley dependent Hall conductivity at the transition points on ballistic transport and reveals the potential of silicene as a topological material for spin-valleytronics.

An aggregate method to calibrate the reference point of cumulative prospect theory-based route choice model for urban transit network

NASA Astrophysics Data System (ADS)

Zhang, Yufeng; Long, Man; Luo, Sida; Bao, Yu; Shen, Hanxia

2015-12-01

Transit route choice model is the key technology of public transit systems planning and management. Traditional route choice models are mostly based on expected utility theory which has an evident shortcoming that it cannot accurately portray travelers' subjective route choice behavior for their risk preferences are not taken into consideration. Cumulative prospect theory (CPT), a brand new theory, can be used to describe travelers' decision-making process under the condition of uncertainty of transit supply and risk preferences of multi-type travelers. The method to calibrate the reference point, a key parameter to CPT-based transit route choice model, determines the precision of the model to a great extent. In this paper, a new method is put forward to obtain the value of reference point which combines theoretical calculation and field investigation results. Comparing the proposed method with traditional method, it shows that the new method can promote the quality of CPT-based model by improving the accuracy in simulating travelers' route choice behaviors based on transit trip investigation from Nanjing City, China. The proposed method is of great significance to logical transit planning and management, and to some extent makes up the defect that obtaining the reference point is solely based on qualitative analysis.

Static quadrupolar susceptibility for a Blume-Emery-Griffiths model based on the mean-field approximation

NASA Astrophysics Data System (ADS)

Pawlak, A.; Gülpınar, G.; Erdem, R.; Ağartıoğlu, M.

2015-12-01

The expressions for the dipolar and quadrupolar susceptibilities are obtained within the mean-field approximation in the Blume-Emery-Griffiths model. Temperature as well as crystal field dependences of the susceptibilities are investigated for two different phase diagram topologies which take place for K/J=3 and K/J=5.0.Their behavior near the second and first order transition points as well as multi-critical points such as tricritical, triple and critical endpoint is presented. It is found that in addition to the jumps connected with the phase transitions there are broad peaks in the quadrupolar susceptibility. It is indicated that these broad peaks lie on a prolongation of the first-order line from a triple point to a critical point ending the line of first-order transitions between two distinct paramagnetic phases. It is argued that the broad peaks are a reminiscence of very strong quadrupolar fluctuations at the critical point. The results reveal the fact that near ferromagnetic-paramagnetic phase transitions the quadrupolar susceptibility generally shows a jump whereas near the phase transition between two distinct paramagnetic phases it is an edge-like.

Reflection technique for thermal mapping of semiconductors

DOEpatents

Walter, Martin J.

1989-06-20

Semiconductors may be optically tested for their temperatures by illuminating them with tunable monochromatic electromagnetic radiation and observing the light reflected off of them. A transition point will occur when the wavelength of the light corresponds with the actual band gap energy of the semiconductor. At the transition point, the image of the semiconductor will appreciably darken as the light is transmitted through it, rather than being reflected off of it. The wavelength of the light at the transition point corresponds to the actual band gap energy and the actual temperature of the semiconductor.

Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holmlid, Leif, E-mail: holmlid@chem.gu.se; Kotzias, Bernhard

Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H{sub 2N}(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H{sub 4}(0) andmore » H{sub 3}(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H{sub 2N}(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected.« less

Breakdown of the Migdal approximation at Lifshitz transitions with giant zero-point motion in the H3S superconductor.

PubMed

Jarlborg, Thomas; Bianconi, Antonio

2016-04-20

While 203 K high temperature superconductivity in H3S has been interpreted by BCS theory in the dirty limit here we focus on the effects of hydrogen zero-point-motion and the multiband electronic structure relevant for multigap superconductivity near Lifshitz transitions. We describe how the topology of the Fermi surfaces evolves with pressure giving different Lifshitz-transitions. A neck-disrupting Lifshitz-transition (type 2) occurs where the van Hove singularity, vHs, crosses the chemical potential at 210 GPa and new small 2D Fermi surface portions appear with slow Fermi velocity where the Migdal-approximation becomes questionable. We show that the neglected hydrogen zero-point motion ZPM, plays a key role at Lifshitz transitions. It induces an energy shift of about 600 meV of the vHs. The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Γ point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations. The maximum Tc = 203 K occurs at 160 GPa where EF/ω0 = 1 in the small Fermi surface pocket at Γ. A Feshbach-like resonance between a possible BEC-BCS condensate at Γ and the BCS condensate in different k-space spots is proposed.

Exotic Lifshitz transitions in topological materials

NASA Astrophysics Data System (ADS)

Volovik, G. E.

2018-01-01

Topological Lifshitz transitions involve many types of topological structures in momentum and frequency-momentum spaces, such as Fermi surfaces, Dirac lines, Dirac and Weyl points, etc., each of which has its own stability-supporting topological invariant ( N_1, N_2, N_3, {\\tilde N}_3, etc.). The topology of the shape of Fermi surfaces and Dirac lines and the interconnection of objects of different dimensionalities produce a variety of Lifshitz transition classes. Lifshitz transitions have important implications for many areas of physics. To give examples, transition-related singularities can increase the superconducting transition temperature; Lifshitz transitions are the possible origin of the small masses of elementary particles in our Universe, and a black hole horizon serves as the surface of the Lifshitz transition between vacua with type-I and type-II Weyl points.

Unconventional quantum criticality emerging as a new common language of transition-metal compounds, heavy-fermion systems, and organic conductors.

PubMed

Imada, Masatoshi; Misawa, Takahiro; Yamaji, Youhei

2010-04-28

We analyze and overview some of the different types of unconventional quantum criticalities by focusing on two origins. One origin of the unconventionality is the proximity to first-order transitions. The border between the first-order and continuous transitions is described by a quantum tricritical point (QTCP) for symmetry breaking transitions. One of the characteristic features of the quantum tricriticality is the concomitant divergence of an order parameter and uniform fluctuations, in contrast to the conventional quantum critical point (QCP). The interplay of these two fluctuations generates unconventionality. Several puzzling non-Fermi-liquid properties in experiments are taken to be accounted for by the resultant universality, as in the cases of Y bRh(2)Si(2), CeRu(2)Si(2) and β-Y bAlB(4). Another more dramatic unconventionality appears again at the border of the first-order and continuous transitions, but in this case for topological transitions such as metal-insulator and Lifshitz transitions. This border, the marginal quantum critical point (MQCP), belongs to an unprecedented universality class with diverging uniform fluctuations at zero temperature. The Ising universality at the critical end point of the first-order transition at nonzero temperatures transforms to the marginal quantum criticality when the critical temperature is suppressed to zero. The MQCP has a unique feature with a combined character of symmetry breaking and topological transitions. In the metal-insulator transitions, the theoretical results are supported by experimental indications for V(2 - x)Cr(x)O(3) and an organic conductor κ-(ET)(2)Cu[N(CN)(2)]Cl. Identifying topological transitions also reveals how non-Fermi liquid appears as a phase in metals. The theory also accounts for the criticality of a metamagnetic transition in ZrZn(2), by interpreting it as an interplay of Lifshitz transition and correlation effects. We discuss the common underlying physics in these examples.

New Transition in the Vortex Liquid State: intrinsic limit of the irreversibility line

NASA Astrophysics Data System (ADS)

Kwok, Wai-Kwong; Paulius, Lisa; Figueras, Jordi

2005-03-01

We have carried out angular dependent magneto-transport measurements on optimally doped, untwinned YBCO crystals irradiated with high energy heavy ions to determine the onset of vortex line tension in the vortex liquid state. The matching field was controlled and kept at a low level to partially preserve the first order vortex lattice melting transition. A Bose glass transition is observed below the lower critical point which then transforms into a first order phase transition near 5 Tesla. The locus of points which indicate the onset of vortex line tension overlaps with the Bose glass transition line at low fields and then deviates at higher fields, indicating a new transition line in the vortex liquid state. This new line in the vortex liquid phase extends beyond the upper critical point.This work was supported by the U.S. Department of Energy, BES, Materials Science under Contract No. W-31-109-ENG-38 at Argonne National Laboratory.

Entanglement entropy of the Q≥4 quantum Potts chain.

PubMed

Lajkó, Péter; Iglói, Ferenc

2017-01-01

The entanglement entropy S is an indicator of quantum correlations in the ground state of a many-body quantum system. At a second-order quantum phase-transition point in one dimension S generally has a logarithmic singularity. Here we consider quantum spin chains with a first-order quantum phase transition, the prototype being the Q-state quantum Potts chain for Q>4 and calculate S across the transition point. According to numerical, density matrix renormalization group results at the first-order quantum phase transition point S shows a jump, which is expected to vanish for Q→4^{+}. This jump is calculated in leading order as ΔS=lnQ[1-4/Q-2/(QlnQ)+O(1/Q^{2})].

Patient-related factors influence stiffness of the soft tissue complex during intraoperative gap balancing in cruciate-retaining total knee arthroplasty.

PubMed

Heesterbeek, P J C; Haffner, N; Wymenga, A B; Stifter, J; Ritschl, P

2017-09-01

How much force is needed to pre-tension the ligaments during total knee arthroplasty? The goal of this study was to determine this force for extension and flexion, and for both compartments, and to identify predicting patient-related factors. Eighty patients [55 females, mean age 71 (SD 9.7)] were recruited and had a navigated cruciate-retaining total knee arthroplasty. Distraction of the medial and lateral compartments of the extension and flexion gap (90°) with an instrumented bi-compartmental double-spring tensioner took place after finishing the bone cuts. Applied forces and resulting gap distances were recorded by the navigation system, resulting in a force-elongation curve. Lines were fitted with the intersection defined as the stiffness transition point. The slopes (N/mm) represented the stiffness of the ligamentous complex. Linear multiple regression analysis was performed to identify predicting factors. The amount of force at the stiffness transition point was on average 52.3 (CI 95 50.7-53.9), 54.5 (CI 95 52.7-56.3), 48.3 (CI 95 46.2-50.2), and 59.3 (CI 95 57.0-61.6) N for the medial and lateral extension and flexion gap, respectively, and varied considerably between patients. The force at the stiffness transition point was significantly different between extension and flexion and both compartments (P < 0.05). Stiffness of the ligaments statistically significantly helped to predict the amount of force at the stiffness transition point, as well as body mass index, gender, and varus-valgus alignment. The amount of force at the stiffness transition point varies between 48 and 59 N, depending on flexion/extension and compartment. Patient-related factors influence the stiffness transition point and can help predict the stiffness transition point. When forces higher than 60 N are used for gap distraction, the ligamentous sleeve of the knee might be over-tensioned. Prognostic study, Level I-high-quality prospective cohort study with >80 % follow-up, and all patients enrolled at same time point in disease.

Correlation and nonlocality measures as indicators of quantum phase transitions in several critical systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altintas, Ferdi, E-mail: ferdialtintas@ibu.edu.tr; Eryigit, Resul, E-mail: resul@ibu.edu.tr

2012-12-15

We have investigated the quantum phase transitions in the ground states of several critical systems, including transverse field Ising and XY models as well as XY with multiple spin interactions, XXZ and the collective system Lipkin-Meshkov-Glick models, by using different quantumness measures, such as entanglement of formation, quantum discord, as well as its classical counterpart, measurement-induced disturbance and the Clauser-Horne-Shimony-Holt-Bell function. Measurement-induced disturbance is found to detect the first and second order phase transitions present in these critical systems, while, surprisingly, it is found to fail to signal the infinite-order phase transition present in the XXZ model. Remarkably, the Clauser-Horne-Shimony-Holt-Bellmore » function is found to detect all the phase transitions, even when quantum and classical correlations are zero for the relevant ground state. - Highlights: Black-Right-Pointing-Pointer The ability of correlation measures to detect quantum phase transitions has been studied. Black-Right-Pointing-Pointer Measurement induced disturbance fails to detect the infinite order phase transition. Black-Right-Pointing-Pointer CHSH-Bell function detects all phase transitions even when the bipartite density matrix is uncorrelated.« less

19 CFR 123.64 - Baggage in transit through the United States between ports in Canada or in Mexico.

Code of Federal Regulations, 2010 CFR

2010-04-01

... between ports in Canada or in Mexico. 123.64 Section 123.64 Customs Duties U.S. CUSTOMS AND BORDER... MEXICO Baggage § 123.64 Baggage in transit through the United States between ports in Canada or in Mexico. (a) Procedure. Baggage in transit from point to point in Canada or Mexico through the United States...

Changes in academic adjustment and relational self-worth across the transition to middle school.

PubMed

Ryan, Allison M; Shim, Sungok Serena; Makara, Kara A

2013-09-01

Moving from elementary to middle school is a time of great transition for many early adolescents. The present study examined students' academic adjustment and relational self-worth at 6-month intervals for four time points spanning the transition from elementary school to middle school (N = 738 at time 1; 53 % girls; 54 % African American, 46 % European American). Grade point average (G.P.A.), intrinsic value for schoolwork, self-worth around teachers, and self-worth around friends were examined at every time point. The overall developmental trajectory indicated that G.P.A. and intrinsic value for schoolwork declined. The overall decline in G.P.A. was due to changes at the transition and across the first year in middle school. Intrinsic value declined across all time points. Self-worth around teachers was stable. The developmental trends were the same regardless of gender or ethnicity except for self-worth around friends, which was stable for European American students and increased for African American students due to an ascent at the transition into middle school. Implications for the education of early adolescents in middle schools are discussed.

Research activities at the Center for Modeling of Turbulence and Transition

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing

1993-01-01

The main research activities at the Center for Modeling of Turbulence and Transition (CMOTT) are described. The research objective of CMOTT is to improve and/or develop turbulence and transition models for propulsion systems. The flows of interest in propulsion systems can be both compressible and incompressible, three dimensional, bounded by complex wall geometries, chemically reacting, and involve 'bypass' transition. The most relevant turbulence and transition models for the above flows are one- and two-equation eddy viscosity models, Reynolds stress algebraic- and transport-equation models, pdf models, and multiple-scale models. All these models are classified as one-point closure schemes since only one-point (in time and space) turbulent correlations, such as second moments (Reynolds stresses and turbulent heat fluxes) and third moments, are involved. In computational fluid dynamics, all turbulent quantities are one-point correlations. Therefore, the study of one-point turbulent closure schemes is the focus of our turbulence research. However, other research, such as the renormalization group theory, the direct interaction approximation method, and numerical simulations are also pursued to support the development of turbulence modeling.

Measurement of a solid-state triple point at the metal-insulator transition in VO2.

PubMed

Park, Jae Hyung; Coy, Jim M; Kasirga, T Serkan; Huang, Chunming; Fei, Zaiyao; Hunter, Scott; Cobden, David H

2013-08-22

First-order phase transitions in solids are notoriously challenging to study. The combination of change in unit cell shape, long range of elastic distortion and flow of latent heat leads to large energy barriers resulting in domain structure, hysteresis and cracking. The situation is worse near a triple point, where more than two phases are involved. The well-known metal-insulator transition in vanadium dioxide, a popular candidate for ultrafast optical and electrical switching applications, is a case in point. Even though VO2 is one of the simplest strongly correlated materials, experimental difficulties posed by the first-order nature of the metal-insulator transition as well as the involvement of at least two competing insulating phases have led to persistent controversy about its nature. Here we show that studying single-crystal VO2 nanobeams in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision. Our results include the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature, Ttr = Tc, which we determine to be 65.0 ± 0.1 °C. The findings have profound implications for the mechanism of the metal-insulator transition in VO2, but they also demonstrate the importance of this approach for mastering phase transitions in many other strongly correlated materials, such as manganites and iron-based superconductors.

An algorithm for minimum-cost set-point ordering in a cryogenic wind tunnel

NASA Technical Reports Server (NTRS)

Tripp, J. S.

1981-01-01

An algorithm for minimum cost ordering of set points in a cryogenic wind tunnel is developed. The procedure generates a matrix of dynamic state transition costs, which is evaluated by means of a single-volume lumped model of the cryogenic wind tunnel and the use of some idealized minimum-costs, which is evaluated by means of a single-volume lumped model of the cryogenic wind tunnel and the use of some idealized minimum-cost state-transition control strategies. A branch and bound algorithm is employed to determine the least costly sequence of state transitions from the transition-cost matrix. Some numerical results based on data for the National Transonic Facility are presented which show a strong preference for state transitions that consume to coolant. Results also show that the choice of the terminal set point in an open odering can produce a wide variation in total cost.

Testing the renormalisation group theory of cooperative transitions at the lambda point of helium

NASA Technical Reports Server (NTRS)

Lipa, J. A.; Li, Q.; Chui, T. C. P.; Marek, D.

1988-01-01

The status of high resolution tests of the renormalization group theory of cooperative phase transitions performed near the lambda point of helium is described. The prospects for performing improved tests in space are discussed.

Network traffic behaviour near phase transition point

NASA Astrophysics Data System (ADS)

Lawniczak, A. T.; Tang, X.

2006-03-01

We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.

Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3

NASA Astrophysics Data System (ADS)

Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.

2018-05-01

Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our recent studies on the compound LaCrGe3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.

Strain-induced topological magnon phase transitions: applications to kagome-lattice ferromagnets

NASA Astrophysics Data System (ADS)

Owerre, S. A.

2018-06-01

A common feature of topological insulators is that they are characterized by topologically invariant quantity such as the Chern number and the index. This quantity distinguishes a nontrivial topological system from a trivial one. A topological phase transition may occur when there are two topologically distinct phases, and it is usually defined by a gap closing point where the topologically invariant quantity is ill-defined. In this paper, we show that the magnon bands in the strained (distorted) kagome-lattice ferromagnets realize an example of a topological magnon phase transition in the realistic parameter regime of the system. When spin–orbit coupling (SOC) is neglected (i.e. no Dzyaloshinskii–Moriya interaction), we show that all three magnon branches are dispersive with no flat band, and there exists a critical point where tilted Dirac and semi-Dirac point coexist in the magnon spectra. The critical point separates two gapless magnon phases as opposed to the usual phase transition. Upon the inclusion of SOC, we realize a topological magnon phase transition point at the critical strain , where D and J denote the perturbative SOC and the Heisenberg spin exchange interaction respectively. It separates two distinct topological magnon phases with different Chern numbers for and for . The associated anomalous thermal Hall conductivity develops an abrupt change at , due to the divergence of the Berry curvature in momentum space. The proposed topological magnon phase transition is experimentally feasible by applying external perturbations such as uniaxial strain or pressure.

Synthesis of Key Points from the OSEP Early Childhood Transition FAQ (SPP/APR Indicators C-8, B-11 and B-12)

ERIC Educational Resources Information Center

Diefendorf, M.; Henson, J.; Lucas, A.; Whaley, K.

2010-01-01

This document is a synthesis of the key points provided in the Office of Special Education Programs (OSEP) Early Childhood Transition FAQs: SPP/APR indicators C-8 and B-12 released on December 1, 2009. It was developed to assist states with the implementation of effective transition policies and practices. The following is included: (1) Transition…

Finite-connectivity spin-glass phase diagrams and low-density parity check codes.

PubMed

Migliorini, Gabriele; Saad, David

2006-02-01

We obtain phase diagrams of regular and irregular finite-connectivity spin glasses. Contact is first established between properties of the phase diagram and the performance of low-density parity check (LDPC) codes within the replica symmetric (RS) ansatz. We then study the location of the dynamical and critical transition points of these systems within the one step replica symmetry breaking theory (RSB), extending similar calculations that have been performed in the past for the Bethe spin-glass problem. We observe that the location of the dynamical transition line does change within the RSB theory, in comparison with the results obtained in the RS case. For LDPC decoding of messages transmitted over the binary erasure channel we find, at zero temperature and rate , an RS critical transition point at while the critical RSB transition point is located at , to be compared with the corresponding Shannon bound . For the binary symmetric channel we show that the low temperature reentrant behavior of the dynamical transition line, observed within the RS ansatz, changes its location when the RSB ansatz is employed; the dynamical transition point occurs at higher values of the channel noise. Possible practical implications to improve the performance of the state-of-the-art error correcting codes are discussed.

Analytic Description of Critical Point Nuclei in a Spherical-Axially Deformed Shape Phase Transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iachello, F.

2001-07-30

An approximate solution at the critical point of the spherical to axially deformed shape phase transition in nuclei is presented. The eigenvalues of the Hamiltonian are expressed in terms of zeros of Bessel functions of irrational order.

Physical implication of transition voltage in organic nano-floating-gate nonvolatile memories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shun; Gao, Xu, E-mail: wangsd@suda.edu.cn, E-mail: gaoxu@suda.edu.cn; Zhong, Ya-Nan

High-performance pentacene-based organic field-effect transistor nonvolatile memories, using polystyrene as a tunneling dielectric and Au nanoparticles as a nano-floating-gate, show parallelogram-like transfer characteristics with a featured transition point. The transition voltage at the transition point corresponds to a threshold electric field in the tunneling dielectric, over which stored electrons in the nano-floating-gate will start to leak out. The transition voltage can be modulated depending on the bias configuration and device structure. For p-type active layers, optimized transition voltage should be on the negative side of but close to the reading voltage, which can simultaneously achieve a high ON/OFF ratio andmore » good memory retention.« less

Finite-density transition line for QCD with 695 MeV dynamical fermions

NASA Astrophysics Data System (ADS)

Greensite, Jeff; Höllwieser, Roman

2018-06-01

We apply the relative weights method to SU(3) gauge theory with staggered fermions of mass 695 MeV at a set of temperatures in the range 151 ≤T ≤267 MeV , to obtain an effective Polyakov line action at each temperature. We then apply a mean field method to search for phase transitions in the effective theory at finite densities. The result is a transition line in the plane of temperature and chemical potential, with an end point at high temperature, as expected, but also a second end point at a lower temperature. We cannot rule out the possibilities that a transition line reappears at temperatures lower than the range investigated, or that the second end point is absent for light quarks.

Mach stem formation in outdoor measurements of acoustic shocks.

PubMed

Leete, Kevin M; Gee, Kent L; Neilsen, Tracianne B; Truscott, Tadd T

2015-12-01

Mach stem formation during outdoor acoustic shock propagation is investigated using spherical oxyacetylene balloons exploded above pavement. The location of the transition point from regular to irregular reflection and the path of the triple point are experimentally resolved using microphone arrays and a high-speed camera. The transition point falls between recent analytical work for weak irregular reflections and an empirical relationship derived from large explosions.

Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.

Some Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our earlier studies on the compound LaCrGe 3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change ofmore » order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.« less

Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe 3

DOE PAGES

Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; ...

2017-08-25

Some Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our earlier studies on the compound LaCrGe 3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change ofmore » order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.« less

Quantum tricritical point in the temperature-pressure-magnetic field phase diagram of CeTiGe 3

DOE PAGES

Kaluarachchi, Udhara S.; Taufour, Valentin; Bud'ko, Sergey L.; ...

2018-01-22

We report the temperature-pressure-magnetic eld phase diagram of the ferromagnetic Kondolattice CeTiGe 3 determined by means of electrical resistivity measurements. Measurements up to ~5.8GPa reveal a rich phase diagram with multiple phase transitions. At ambient pressure, CeTiGe 3 orders ferromagnetically at T C =14 K. Application of pressure suppresses T C, but a pressure induced ferromagnetic quantum criticality is avoided by the appearance of two new successive transitions for p>4.1GPa that are probably antiferromagnetic in nature. These two transitions are suppressed under pressure, with the lower temperature phase being fully suppressed above 5.3GPa. The critical pressures for the presumed quantummore » phase transitions are p1≅4.1GPa and p2≅5.3GPa. Above 4.1GPa, application of magnetic eld shows a tricritical point evolving into a wing structure phase with a quantum tricritical point at 2.8T at 5.4GPa, where the rst order antiferromagneticferromagnetic transition changes into the second order antiferromagnetic-ferromagnetic transition.« less

Dynamic phase transitions of the Blume-Emery-Griffiths model under an oscillating external magnetic field by the path probability method

NASA Astrophysics Data System (ADS)

Ertaş, Mehmet; Keskin, Mustafa

2015-03-01

By using the path probability method (PPM) with point distribution, we study the dynamic phase transitions (DPTs) in the Blume-Emery-Griffiths (BEG) model under an oscillating external magnetic field. The phases in the model are obtained by solving the dynamic equations for the average order parameters and a disordered phase, ordered phase and four mixed phases are found. We also investigate the thermal behavior of the dynamic order parameters to analyze the nature dynamic transitions as well as to obtain the DPT temperatures. The dynamic phase diagrams are presented in three different planes in which exhibit the dynamic tricritical point, double critical end point, critical end point, quadrupole point, triple point as well as the reentrant behavior, strongly depending on the values of the system parameters. We compare and discuss the dynamic phase diagrams with dynamic phase diagrams that were obtained within the Glauber-type stochastic dynamics based on the mean-field theory.

Quantum transitions through cosmological singularities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bramberger, Sebastian F.; Lehners, Jean-Luc; Hertog, Thomas

2017-07-01

In a quantum theory of cosmology spacetime behaves classically only in limited patches of the configuration space on which the wave function of the universe is defined. Quantum transitions can connect classical evolution in different patches. Working in the saddle point approximation and in minisuperspace we compute quantum transitions connecting inflationary histories across a de Sitter like throat or a singularity. This supplies probabilities for how an inflating universe, when evolved backwards, transitions and branches into an ensemble of histories on the opposite side of a quantum bounce. Generalising our analysis to scalar potentials with negative regions we identify saddlemore » points describing a quantum transition between a classically contracting, crunching ekpyrotic phase and an inflationary universe.« less

Quantum transitions through cosmological singularities

NASA Astrophysics Data System (ADS)

Bramberger, Sebastian F.; Hertog, Thomas; Lehners, Jean-Luc; Vreys, Yannick

2017-07-01

In a quantum theory of cosmology spacetime behaves classically only in limited patches of the configuration space on which the wave function of the universe is defined. Quantum transitions can connect classical evolution in different patches. Working in the saddle point approximation and in minisuperspace we compute quantum transitions connecting inflationary histories across a de Sitter like throat or a singularity. This supplies probabilities for how an inflating universe, when evolved backwards, transitions and branches into an ensemble of histories on the opposite side of a quantum bounce. Generalising our analysis to scalar potentials with negative regions we identify saddle points describing a quantum transition between a classically contracting, crunching ekpyrotic phase and an inflationary universe.

Refined geometric transition and qq-characters

NASA Astrophysics Data System (ADS)

Kimura, Taro; Mori, Hironori; Sugimoto, Yuji

2018-01-01

We show the refinement of the prescription for the geometric transition in the refined topological string theory and, as its application, discuss a possibility to describe qq-characters from the string theory point of view. Though the suggested way to operate the refined geometric transition has passed through several checks, it is additionally found in this paper that the presence of the preferred direction brings a nontrivial effect. We provide the modified formula involving this point. We then apply our prescription of the refined geometric transition to proposing the stringy description of doubly quantized Seiberg-Witten curves called qq-characters in certain cases.

Role of dimensionality in Axelrod's model for the dissemination of culture

NASA Astrophysics Data System (ADS)

Klemm, Konstantin; Eguíluz, Víctor M.; Toral, Raúl; Miguel, Maxi San

2003-09-01

We analyze a model of social interaction in one- and two-dimensional lattices for a moderate number of features. We introduce an order parameter as a function of the overlap between neighboring sites. In a one-dimensional chain, we observe that the dynamics is consistent with a second-order transition, where the order parameter changes continuously and the average domain diverges at the transition point. However, in a two-dimensional lattice the order parameter is discontinuous at the transition point characteristic of a first-order transition between an ordered and a disordered state.

Non-equilibrium phase transitions in a driven-dissipative system of interacting bosons

NASA Astrophysics Data System (ADS)

Young, Jeremy T.; Foss-Feig, Michael; Gorshkov, Alexey V.; Maghrebi, Mohammad F.

2017-04-01

Atomic, molecular, and optical systems provide unique opportunities to study simple models of driven-dissipative many-body quantum systems. Typically, one is interested in the resultant steady state, but the non-equilibrium nature of the physics involved presents several problems in understanding its behavior theoretically. Recently, it has been shown that in many of these models, it is possible to map the steady-state phase transitions onto classical equilibrium phase transitions. In the language of Keldysh field theory, this relation typically only becomes apparent after integrating out massive fields near the critical point, leaving behind a single massless field undergoing near-equilibrium dynamics. In this talk, we study a driven-dissipative XXZ bosonic model and discover critical points at which two fields become gapless. Each critical point separates three different possible phases: a uniform phase, an anti-ferromagnetic phase, and a limit cycle phase. Furthermore, a description in terms of an equilibrium phase transition does not seem possible, so the associated phase transitions appear to be inherently non-equilibrium.

Strain-induced topological magnon phase transitions: applications to kagome-lattice ferromagnets.

PubMed

Owerre, S A

2018-06-20

A common feature of topological insulators is that they are characterized by topologically invariant quantity such as the Chern number and the [Formula: see text] index. This quantity distinguishes a nontrivial topological system from a trivial one. A topological phase transition may occur when there are two topologically distinct phases, and it is usually defined by a gap closing point where the topologically invariant quantity is ill-defined. In this paper, we show that the magnon bands in the strained (distorted) kagome-lattice ferromagnets realize an example of a topological magnon phase transition in the realistic parameter regime of the system. When spin-orbit coupling (SOC) is neglected (i.e. no Dzyaloshinskii-Moriya interaction), we show that all three magnon branches are dispersive with no flat band, and there exists a critical point where tilted Dirac and semi-Dirac point coexist in the magnon spectra. The critical point separates two gapless magnon phases as opposed to the usual phase transition. Upon the inclusion of SOC, we realize a topological magnon phase transition point at the critical strain [Formula: see text], where D and J denote the perturbative SOC and the Heisenberg spin exchange interaction respectively. It separates two distinct topological magnon phases with different Chern numbers for [Formula: see text] and for [Formula: see text]. The associated anomalous thermal Hall conductivity develops an abrupt change at [Formula: see text], due to the divergence of the Berry curvature in momentum space. The proposed topological magnon phase transition is experimentally feasible by applying external perturbations such as uniaxial strain or pressure.

Modelling Phase Transition Phenomena in Fluids

DTIC Science & Technology

2015-07-01

Sublimation line r @@I Triple point ? Vapourisation liner @@I Critical point -Fusion line Solid Liquid Gas Figure 1: Schematic of a phase diagram means that the...velocity field can be set zero, and only the balance of energy constitutes the Stefan model. In contrast to this the liquid - gas phase transitions...defined by requiring that the phase-transition line is crossed in a direction from solid to liquid or from liquid to gas (vapour) phases. The term T∗ δs is

Davies Critical Point and Tunneling

NASA Astrophysics Data System (ADS)

La, Hoseong

2012-04-01

From the point of view of tunneling, the physical meaning of the Davies critical point of a second-order phase transition in the black hole thermodynamics is clarified. At the critical point, the nonthermal contribution vanishes so that the black hole radiation is entirely thermal. It separates two phases: one with radiation enhanced by the nonthermal contribution, the other suppressed by the nonthermal contribution. We show this in both charged and rotating black holes. The phase transition is also analyzed in the cases in which emissions of charges and angular momenta are incorporated.

Quantum coherence of planar spin models with Dzyaloshinsky-Moriya interaction

NASA Astrophysics Data System (ADS)

Radhakrishnan, Chandrashekar; Ermakov, Igor; Byrnes, Tim

2017-07-01

The quantum coherence of one-dimensional planar spin models with Dzyaloshinsky-Moriya interaction is investigated. The anisotropic XY model, the isotropic XX model, and the transverse field model are studied in the large N limit using two qubit reduced density matrices and two point correlation functions. From our investigations we find that the coherence as measured using Jensen-Shannon divergence can be used to detect quantum phase transitions and quantum critical points. The derivative of coherence shows nonanalytic behavior at critical points, leading to the conclusion that these transitions are of second order. Further, we show that the presence of Dzyaloshinsky-Moriya coupling suppresses the phase transition due to residual ferromagnetism, which is caused by spin canting.

Vortex flow hysteresis

NASA Technical Reports Server (NTRS)

Cunningham, A. M., Jr.

1986-01-01

An experimental study was conducted to quantify the hysteresis associated with various vortex flow transition points and to determine the effect of planform geometry. The transition points observed consisted of the appearance (or disappearance) of trailing edge vortex burst and the transition to (or from) flat plate or totally separated flows. Flow visualization with smoke injected into the vortices was used to identify the transitions on a series of semi-span models tested in a low speed tunnel. The planforms tested included simple deltas (55 deg to 80 deg sweep), cranked wings with varying tip panel sweep and dihedral, and a straked wing. High speed movies at 1000 frames per second were made of the vortex flow visualization in order to better understand the dynamics of vortex flow, burst and transition.

Shear-induced criticality near a liquid-solid transition of colloidal suspensions

NASA Astrophysics Data System (ADS)

Miyama, Masamichi J.; Sasa, Shin-Ichi

2011-02-01

We investigate colloidal suspensions under shear flow through numerical experiments. By measuring the time-correlation function of a bond-orientational order parameter, we find a divergent time scale near a transition point from a disordered fluid phase to an ordered fluid phase, where the order is characterized by a nonzero value of the bond-orientational order parameter. We also present a phase diagram in the (ρ,γ˙ex) plane, where ρ is the density of the colloidal particles and γ˙ex is the shear rate of the solvent. The transition line in the phase diagram terminates at the equilibrium transition point, while a critical region near the transition line vanishes continuously as γ˙ex→0.

Navy Stock Point Local Unique Computer Programs: An Analysis for Transition and Management Under the Stock Point ADP Replacement (SPAR) Project.

DTIC Science & Technology

1987-03-01

Project (SPAR). An impor- tant issue of the replacement will be the conversion of existing co uter software to allow transition from the current... issue of the replacement will be the conversion of existing computer software to allow transition from the current hardware environment to the replacement...36 G. LOCAL PROGRAM C1/C2 CONVERSION CONTRACT . . . 38 5 H. LOCAL PROGRAM COMMONALITY ISSUES ....... 41 I. SUMMARY

A path-integral approach to the problem of time

NASA Astrophysics Data System (ADS)

Amaral, M. M.; Bojowald, Martin

2018-01-01

Quantum transition amplitudes are formulated for model systems with local internal time, using intuition from path integrals. The amplitudes are shown to be more regular near a turning point of internal time than could be expected based on existing canonical treatments. In particular, a successful transition through a turning point is provided in the model systems, together with a new definition of such a transition in general terms. Some of the results rely on a fruitful relation between the problem of time and general Gribov problems.

Absorbing phase transitions in deterministic fixed-energy sandpile models

NASA Astrophysics Data System (ADS)

Park, Su-Chan

2018-03-01

We investigate the origin of the difference, which was noticed by Fey et al. [Phys. Rev. Lett. 104, 145703 (2010), 10.1103/PhysRevLett.104.145703], between the steady state density of an Abelian sandpile model (ASM) and the transition point of its corresponding deterministic fixed-energy sandpile model (DFES). Being deterministic, the configuration space of a DFES can be divided into two disjoint classes such that every configuration in one class should evolve into one of absorbing states, whereas no configurations in the other class can reach an absorbing state. Since the two classes are separated in terms of toppling dynamics, the system can be made to exhibit an absorbing phase transition (APT) at various points that depend on the initial probability distribution of the configurations. Furthermore, we show that in general the transition point also depends on whether an infinite-size limit is taken before or after the infinite-time limit. To demonstrate, we numerically study the two-dimensional DFES with Bak-Tang-Wiesenfeld toppling rule (BTW-FES). We confirm that there are indeed many thresholds. Nonetheless, the critical phenomena at various transition points are found to be universal. We furthermore discuss a microscopic absorbing phase transition, or a so-called spreading dynamics, of the BTW-FES, to find that the phase transition in this setting is related to the dynamical isotropic percolation process rather than self-organized criticality. In particular, we argue that choosing recurrent configurations of the corresponding ASM as an initial configuration does not allow for a nontrivial APT in the DFES.

Absorbing phase transitions in deterministic fixed-energy sandpile models.

PubMed

Park, Su-Chan

2018-03-01

We investigate the origin of the difference, which was noticed by Fey et al. [Phys. Rev. Lett. 104, 145703 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.145703], between the steady state density of an Abelian sandpile model (ASM) and the transition point of its corresponding deterministic fixed-energy sandpile model (DFES). Being deterministic, the configuration space of a DFES can be divided into two disjoint classes such that every configuration in one class should evolve into one of absorbing states, whereas no configurations in the other class can reach an absorbing state. Since the two classes are separated in terms of toppling dynamics, the system can be made to exhibit an absorbing phase transition (APT) at various points that depend on the initial probability distribution of the configurations. Furthermore, we show that in general the transition point also depends on whether an infinite-size limit is taken before or after the infinite-time limit. To demonstrate, we numerically study the two-dimensional DFES with Bak-Tang-Wiesenfeld toppling rule (BTW-FES). We confirm that there are indeed many thresholds. Nonetheless, the critical phenomena at various transition points are found to be universal. We furthermore discuss a microscopic absorbing phase transition, or a so-called spreading dynamics, of the BTW-FES, to find that the phase transition in this setting is related to the dynamical isotropic percolation process rather than self-organized criticality. In particular, we argue that choosing recurrent configurations of the corresponding ASM as an initial configuration does not allow for a nontrivial APT in the DFES.

Mixed-order phase transition in a two-step contagion model with a single infectious seed.

PubMed

Choi, Wonjun; Lee, Deokjae; Kahng, B

2017-02-01

Percolation is known as one of the most robust continuous transitions, because its occupation rule is intrinsically local. As one of the ways to break the robustness, occupation is allowed to more than one species of particles and they occupy cooperatively. This generalized percolation model undergoes a discontinuous transition. Here we investigate an epidemic model with two contagion steps and characterize its phase transition analytically and numerically. We find that even though the order parameter jumps at a transition point r_{c}, then increases continuously, it does not exhibit any critical behavior: the fluctuations of the order parameter do not diverge at r_{c}. However, critical behavior appears in mean outbreak size, which diverges at the transition point in a manner that the ordinary percolation shows. Such a type of phase transition is regarded as a mixed-order phase transition. We also obtain scaling relations of cascade outbreak statistics when the order parameter jumps at r_{c}.

Anomalous critical slowdown at a first order phase transition in single polymer chains.

PubMed

Zhang, Shuangshuang; Qi, Shuanhu; Klushin, Leonid I; Skvortsov, Alexander M; Yan, Dadong; Schmid, Friederike

2017-08-14

Using Brownian dynamics, we study the dynamical behavior of a polymer grafted onto an adhesive surface close to the mechanically induced adsorption-stretching transition. Even though the transition is first order (in the infinite chain length limit, the stretching degree of the chain jumps discontinuously), the characteristic relaxation time is found to grow according to a power law as the transition point is approached. We present a dynamic effective interface model which reproduces these observations and provides an excellent quantitative description of the simulation data. The generic nature of the theoretical model suggests that the unconventional mixing of features that are characteristic for first-order transitions (a jump in an order parameter) and features that are characteristic of critical points (an anomalous slowdown) may be a common phenomenon in force-driven phase transitions of macromolecules.

Cocrystal Transition Points: Role of Cocrystal Solubility, Drug Solubility, and Solubilizing Agents.

PubMed

Lipert, Maya P; Rodríguez-Hornedo, Naír

2015-10-05

In this manuscript we bring together concepts that are relevant to the solubilization and thermodynamic stability of cocrystals in the presence of drug solubilizing agents. Simple equations are derived that allow calculation of cocrystal solubilization and transition point solubility. Analysis of 10 cocrystals in 6 different solubilizing agents shows that cocrystal solubilization is quantitatively predicted from drug solubilization. Drug solubilizing agents such as surfactants and lipid-based media are also shown to induce cocrystal transition points, where drug and cocrystal solubilities are equal, and above which the cocrystal solubility advantage over drug is eliminated. We have discovered that cocrystal solubility at the transition point (S*) is independent of solubilizing agent, and can be predicted from knowledge of only the aqueous solubilities of drug and cocrystal. For 1:1 cocrystals, S* = (Scocrystal,aq)(2)/Sdrug,aq. S* is a key indicator of cocrystal thermodynamic stability and establishes the upper solubility limit below which cocrystal is more soluble than the constituent drug. These findings have important implications to tailor cocrystal solubility and stability in pharmaceutical formulations from commonly available drug solubility descriptors.

Mixed-order phase transition in a minimal, diffusion-based spin model.

PubMed

Fronczak, Agata; Fronczak, Piotr

2016-07-01

In this paper we exactly solve, within the grand canonical ensemble, a minimal spin model with the hybrid phase transition. We call the model diffusion based because its Hamiltonian can be recovered from a simple dynamic procedure, which can be seen as an equilibrium statistical mechanics representation of a biased random walk. We outline the derivation of the phase diagram of the model, in which the triple point has the hallmarks of the hybrid transition: discontinuity in the average magnetization and algebraically diverging susceptibilities. At this point, two second-order transition curves meet in equilibrium with the first-order curve, resulting in a prototypical mixed-order behavior.

Electronic topological transitions in Zn under compression

NASA Astrophysics Data System (ADS)

Kechin, Vladimir V.

2001-01-01

The electronic structure of hcp Zn under pressure up to 10 GPa has been calculated self-consistently by means of the scalar relativistic tight-binding linear muffin-tin orbital method. The calculations show that three electronic topological transitions (ETT's) occur in Zn when the c/a axial ratio diminishes under compression. One transition occurs at c/a~=1.82 when the ``needles'' appear around the symmetry point K of the Brillouin zone. The other two transitions occur at c/a~=3, when the ``butterfly'' and ``cigar'' appear simultaneously both around the L point. It has been shown that these ETT's are responsible for a number of anomalies observed in Zn at compression.

Hybrid phase transition into an absorbing state: Percolation and avalanches

NASA Astrophysics Data System (ADS)

Lee, Deokjae; Choi, S.; Stippinger, M.; Kertész, J.; Kahng, B.

2016-04-01

Interdependent networks are more fragile under random attacks than simplex networks, because interlayer dependencies lead to cascading failures and finally to a sudden collapse. This is a hybrid phase transition (HPT), meaning that at the transition point the order parameter has a jump but there are also critical phenomena related to it. Here we study these phenomena on the Erdős-Rényi and the two-dimensional interdependent networks and show that the hybrid percolation transition exhibits two kinds of critical behaviors: divergence of the fluctuations of the order parameter and power-law size distribution of finite avalanches at a transition point. At the transition point global or "infinite" avalanches occur, while the finite ones have a power law size distribution; thus the avalanche statistics also has the nature of a HPT. The exponent βm of the order parameter is 1 /2 under general conditions, while the value of the exponent γm characterizing the fluctuations of the order parameter depends on the system. The critical behavior of the finite avalanches can be described by another set of exponents, βa and γa. These two critical behaviors are coupled by a scaling law: 1 -βm=γa .

Kerr-AdS analogue of triple point and solid/liquid/gas phase transition

NASA Astrophysics Data System (ADS)

Altamirano, Natacha; Kubizňák, David; Mann, Robert B.; Sherkatghanad, Zeinab

2014-02-01

We study the thermodynamic behavior of multi-spinning d = 6 Kerr-anti de Sitter black holes in the canonical ensemble of fixed angular momenta J1 and J2. We find, dependent on the ratio q = J2/J1, qualitatively different interesting phenomena known from the ‘every day thermodynamics’ of simple substances. For q = 0 the system exhibits recently observed reentrant large/small/large black hole phase transitions, but for 0 < q ≪ 1 we find an analogue of a ‘solid/liquid’ phase transition. Furthermore, for q ∈ (0.00905, 0.0985) the system displays the presence of a large/intermediate/small black hole phase transition with two critical and one triple (or tricritical) points. This behavior is reminiscent of the solid/liquid/gas phase transition except that the coexistence line of small and intermediate black holes does not continue for an arbitrary value of pressure (similar to the solid/liquid coexistence line) but rather terminates at one of the critical points. Finally, for q > 0.0985 we observe the ‘standard liquid/gas behavior’ of the Van der Waals fluid.

Resonance and Capture of Jupiter Comets

NASA Astrophysics Data System (ADS)

Koon, W. S.; Lo, M. W.; Marsden, J. E.; Ross, S. D.

A number of Jupiter family comets such as Oterma and Gehrels 3 make a rapid transition from heliocentric orbits outside the orbit of Jupiter to heliocentric orbits inside the orbit of Jupiter and vice versa. During this transition, the comet can be captured temporarily by Jupiter for one to several orbits around Jupiter. The interior heliocentric orbit is typically close to the 3:2 resonance while the exterior heliocentric orbit is near the 2:3 resonance. An important feature of the dynamics of these comets is that during the transition, the orbit passes close to the libration points L_1 and L_2, two of the equilibrium points for the restricted three-body problem for the Sun-Jupiter system. Studying the libration point invariant manifold structures for L_1 and L_2 is a starting point for understanding the capture and resonance transition of these comets. For example, the recently discovered heteroclinic connection between pairs of unstable periodic orbits (one around the L_1 and the other around L_2) implies a complicated dynamics for comets in a certain energy range. Furthermore, the stable and unstable invariant manifold `tubes' associated to libration point periodic orbits, of which the heteroclinic connections are a part, are phase space conduits transporting material to and from Jupiter and between the interior and exterior of Jupiter's orbit.

Multiple tipping points and optimal repairing in interacting networks

PubMed Central

Majdandzic, Antonio; Braunstein, Lidia A.; Curme, Chester; Vodenska, Irena; Levy-Carciente, Sary; Eugene Stanley, H.; Havlin, Shlomo

2016-01-01

Systems composed of many interacting dynamical networks—such as the human body with its biological networks or the global economic network consisting of regional clusters—often exhibit complicated collective dynamics. Three fundamental processes that are typically present are failure, damage spread and recovery. Here we develop a model for such systems and find a very rich phase diagram that becomes increasingly more complex as the number of interacting networks increases. In the simplest example of two interacting networks we find two critical points, four triple points, ten allowed transitions and two ‘forbidden' transitions, as well as complex hysteresis loops. Remarkably, we find that triple points play the dominant role in constructing the optimal repairing strategy in damaged interacting systems. To test our model, we analyse an example of real interacting financial networks and find evidence of rapid dynamical transitions between well-defined states, in agreement with the predictions of our model. PMID:26926803

Thermodynamics and glassy phase transition of regular black holes

NASA Astrophysics Data System (ADS)

Javed, Wajiha; Yousaf, Z.; Akhtar, Zunaira

2018-05-01

This paper is aimed to study thermodynamical properties of phase transition for regular charged black holes (BHs). In this context, we have considered two different forms of BH metrics supplemented with exponential and logistic distribution functions and investigated the recent expansion of phase transition through grand canonical ensemble. After exploring the corresponding Ehrenfest’s equation, we found the second-order background of phase transition at critical points. In order to check the critical behavior of regular BHs, we have evaluated some corresponding explicit relations for the critical temperature, pressure and volume and draw certain graphs with constant values of Smarr’s mass. We found that for the BH metric with exponential configuration function, the phase transition curves are divergent near the critical points, while glassy phase transition has been observed for the Ayón-Beato-García-Bronnikov (ABGB) BH in n = 5 dimensions.

Engineering Surface Critical Behavior of (2 +1 )-Dimensional O(3) Quantum Critical Points

NASA Astrophysics Data System (ADS)

Ding, Chengxiang; Zhang, Long; Guo, Wenan

2018-06-01

Surface critical behavior (SCB) refers to the singularities of physical quantities on the surface at the bulk phase transition. It is closely related to and even richer than the bulk critical behavior. In this work, we show that three types of SCB universality are realized in the dimerized Heisenberg models at the (2 +1 )-dimensional O(3) quantum critical points by engineering the surface configurations. The ordinary transition happens if the surface is gapped in the bulk disordered phase, while the gapless surface state generally leads to the multicritical special transition, even though the latter is precluded in classical phase transitions because the surface is in the lower critical dimension. An extraordinary transition is induced by the ferrimagnetic order on the surface of the staggered Heisenberg model, in which the surface critical exponents violate the results of the scaling theory and thus seriously challenge our current understanding of extraordinary transitions.

Nontrivial Critical Fixed Point for Replica-Symmetry-Breaking Transitions.

PubMed

Charbonneau, Patrick; Yaida, Sho

2017-05-26

The transformation of the free-energy landscape from smooth to hierarchical is one of the richest features of mean-field disordered systems. A well-studied example is the de Almeida-Thouless transition for spin glasses in a magnetic field, and a similar phenomenon-the Gardner transition-has recently been predicted for structural glasses. The existence of these replica-symmetry-breaking phase transitions has, however, long been questioned below their upper critical dimension, d_{u}=6. Here, we obtain evidence for the existence of these transitions in d

Absolute frequency of cesium 6S-8S 822 nm two-photon transition by a high-resolution scheme.

PubMed

Wu, Chien-Ming; Liu, Tze-Wei; Wu, Ming-Hsuan; Lee, Ray-Kuang; Cheng, Wang-Yau

2013-08-15

We present an alternative scheme for determining the frequencies of cesium (Cs) atom 6S-8S Doppler-free transitions. With the use of a single electro-optical crystal, we simultaneously narrow the laser linewidth, lock the laser frequency, and resolve a narrow spectrum point by point. The error budget for this scheme is presented, and we prove that the transition frequency obtained from the Cs cell at room temperature and with one-layer μ-metal shielding is already very near that for the condition of zero collision and zero magnetic field. We point out that a sophisticated linewidth measurement could be a good guidance for choosing a suitable Cs cell for better frequency accuracy.

Bio-optical profile data report coastal transition zone program, R/V Point Sur, June 15-28, 1987

NASA Technical Reports Server (NTRS)

Davis, Curtiss O.; Rhea, W. Joseph

1990-01-01

Twenty vertical profiles of the bio-optical properties of the ocean were made during a research cruise on the R/V Point Sur, June 15 to 28, 1987, as part of the Coastal Transition Zone Program off Point Arena, California. Extracted chlorophyll values were also measured at some stations to provide calibration data for the in situ fluorometer. This summary provides investigators with an overview of the data collected. The entire data set is available in digital form.

Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk.

PubMed

Guttal, Vishwesha; Raghavendra, Srinivas; Goel, Nikunj; Hoarau, Quentin

2016-01-01

Complex systems inspired analysis suggests a hypothesis that financial meltdowns are abrupt critical transitions that occur when the system reaches a tipping point. Theoretical and empirical studies on climatic and ecological dynamical systems have shown that approach to tipping points is preceded by a generic phenomenon called critical slowing down, i.e. an increasingly slow response of the system to perturbations. Therefore, it has been suggested that critical slowing down may be used as an early warning signal of imminent critical transitions. Whether financial markets exhibit critical slowing down prior to meltdowns remains unclear. Here, our analysis reveals that three major US (Dow Jones Index, S&P 500 and NASDAQ) and two European markets (DAX and FTSE) did not exhibit critical slowing down prior to major financial crashes over the last century. However, all markets showed strong trends of rising variability, quantified by time series variance and spectral function at low frequencies, prior to crashes. These results suggest that financial crashes are not critical transitions that occur in the vicinity of a tipping point. Using a simple model, we argue that financial crashes are likely to be stochastic transitions which can occur even when the system is far away from the tipping point. Specifically, we show that a gradually increasing strength of stochastic perturbations may have caused to abrupt transitions in the financial markets. Broadly, our results highlight the importance of stochastically driven abrupt transitions in real world scenarios. Our study offers rising variability as a precursor of financial meltdowns albeit with a limitation that they may signal false alarms.

Interprofessional simulation to improve patient participation in transitional care.

PubMed

Dyrstad, Dagrunn Nåden; Storm, Marianne

2017-06-01

Educating and training healthcare professionals is known to improve the quality of transitional care for older adults. Arranging interprofessional meetings for healthcare professionals might be useful to improve patient participation skills in transitional care. To describe the learning activities used in The Meeting Point programme, focusing on patient participation in transitional care, and assess whether they increase healthcare professionals' awareness of and competencies relating to patient participation in the transitional care of older patients. Data were collected as part of an educational intervention programme, The Meeting Point, including three seminars on 'Patient participation in the transitional care of older patients' and four follow-up meetings. Participants were nurses, care assistants, doctors, physiotherapists, patient coordinators and administrative personnel from hospital, nursing homes and home-based care services. The Meeting Point was organised around four pillars: introduction, teaching session, group work activity and plenary discussion. Qualitative data included log reports, summaries of meetings, notes from group work activities, and reports from participants and from follow-up meetings. Feedback from participants shows that they were satisfied with meeting healthcare professionals from other units of care. A film scenario was perceived relevant for group work activity and useful in focusing participants' attention to patient participation. Follow-up meetings show that some nursing home wards, the emergency department and one medical ward at the hospital continued with ongoing work to improve quality of care. Efforts included implementation of an observational waiting room with comfortable chairs, planning for discharge in hospital admission, a daily patient flow registration system and motivational interviewing during admission to nursing home. The description of the learning activities used at The Meeting Point seminars shows that they were useful to increase awareness of and competencies on patient participation in transitional care. © 2016 Nordic College of Caring Science.

Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk

PubMed Central

Hoarau, Quentin

2016-01-01

Complex systems inspired analysis suggests a hypothesis that financial meltdowns are abrupt critical transitions that occur when the system reaches a tipping point. Theoretical and empirical studies on climatic and ecological dynamical systems have shown that approach to tipping points is preceded by a generic phenomenon called critical slowing down, i.e. an increasingly slow response of the system to perturbations. Therefore, it has been suggested that critical slowing down may be used as an early warning signal of imminent critical transitions. Whether financial markets exhibit critical slowing down prior to meltdowns remains unclear. Here, our analysis reveals that three major US (Dow Jones Index, S&P 500 and NASDAQ) and two European markets (DAX and FTSE) did not exhibit critical slowing down prior to major financial crashes over the last century. However, all markets showed strong trends of rising variability, quantified by time series variance and spectral function at low frequencies, prior to crashes. These results suggest that financial crashes are not critical transitions that occur in the vicinity of a tipping point. Using a simple model, we argue that financial crashes are likely to be stochastic transitions which can occur even when the system is far away from the tipping point. Specifically, we show that a gradually increasing strength of stochastic perturbations may have caused to abrupt transitions in the financial markets. Broadly, our results highlight the importance of stochastically driven abrupt transitions in real world scenarios. Our study offers rising variability as a precursor of financial meltdowns albeit with a limitation that they may signal false alarms. PMID:26761792

The phase transitions between Z n × Z n bosonic topological phases in 1 + 1D, and a constraint on the central charge for the critical points between bosonic symmetry protected topological phases

DOE PAGES

Tsui, Lokman; Huang, Yen-Ta; Jiang, Hong-Chen; ...

2017-03-27

The study of continuous phase transitions triggered by spontaneous symmetry breaking has brought revolutionary ideas to physics. Recently, through the discovery of symmetry protected topological phases, it is realized that continuous quantum phase transition can also occur between states with the same symmetry but different topology. Here in this paper we study a specific class of such phase transitions in 1+1 dimensions – the phase transition between bosonic topological phases protected by Z n × Z n. We find in all cases the critical point possesses two gap opening relevant operators: one leads to a Landau-forbidden symmetry breaking phase transitionmore » and the other to the topological phase transition. We also obtained a constraint on the central charge for general phase transitions between symmetry protected bosonic topological phases in 1+1D.« less

The phase transitions between Z n × Z n bosonic topological phases in 1 + 1D, and a constraint on the central charge for the critical points between bosonic symmetry protected topological phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsui, Lokman; Huang, Yen-Ta; Jiang, Hong-Chen

The study of continuous phase transitions triggered by spontaneous symmetry breaking has brought revolutionary ideas to physics. Recently, through the discovery of symmetry protected topological phases, it is realized that continuous quantum phase transition can also occur between states with the same symmetry but different topology. Here in this paper we study a specific class of such phase transitions in 1+1 dimensions – the phase transition between bosonic topological phases protected by Z n × Z n. We find in all cases the critical point possesses two gap opening relevant operators: one leads to a Landau-forbidden symmetry breaking phase transitionmore » and the other to the topological phase transition. We also obtained a constraint on the central charge for general phase transitions between symmetry protected bosonic topological phases in 1+1D.« less

[Transition from pediatric to adult health care services for adolescents with chronic diseases: Recommendations from the Adolescent Branch from Sociedad Chilena de Pediatría].

PubMed

Zubarew, Tamara; Correa, Loreto; Bedregal, Paula; Besoain, Carolina; Reinoso, Alejandro; Velarde, Macarena; Valenzuela, María Teresa; Inostroza, Carolina

2017-01-01

The Adolescent Branch from Sociedad Chilena de Pediatría supports the implementation of planned programs for transition from child to adult health centers, oriented to adolescents with chronic diseases, in order to ensure an appropriate follow-up and a high-quality health care. Recommendations for care are set out in the FONIS and VRI PUC project carried out by the Division of Pediatrics of the Universidad Católica de Chile: “Transition process from pediatric to adult services: perspectives of adolescents with chronic diseases, caregivers and health professionals”, whose goal was to describe the experience, barriers, critical points, and facilitators in the transition process. Critical points detected in this study were: existence of a strong bond between adolescents, caregivers and the pediatric team, resistance to transition, difficulty developing autonomy and self-management among adolescents; invisibility of the process of adolescence; and lack of communication between pediatric and adult team during the transfer. According to these needs, barriers and critical points, and based on published international experiences, recommendations are made for implementation of gradual and planned transition processes, with emphasis on the design and implementation of transition policies, establishment of multidisciplinary teams and transition planning. We discuss aspects related to coordination of teams, transfer timing, self-care and autonomy, transition records, adolescent and family participation, need for emotional support, ethical aspects involved, importance of confidentiality, need for professional training, and the need for evaluation and further research on the subject.

Transmutation of a trans-series: the Gross-Witten-Wadia phase transition

NASA Astrophysics Data System (ADS)

Ahmed, Anees; Dunne, Gerald V.

2017-11-01

We study the change in the resurgent asymptotic properties of a trans-series in two parameters, a coupling g 2 and a gauge index N, as a system passes through a large N phase transition, using the universal example of the Gross-Witten-Wadia third-order phase transition in the unitary matrix model. This transition is well-studied in the immediate vicinity of the transition point, where it is characterized by a double-scaling limit Painlevé II equation, and also away from the transition point using the pre-string difference equation. Here we present a complementary analysis of the transition at all coupling and all finite N, in terms of a differential equation, using the explicit Tracy-Widom mapping of the Gross-Witten-Wadia partition function to a solution of a Painlevé III equation. This mapping provides a simple method to generate trans-series expansions in all parameter regimes, and to study their transmutation as the parameters are varied. For example, at any finite N the weak coupling expansion is divergent, with a non-perturbative trans-series completion; on the other hand, the strong coupling expansion is convergent, and yet there is still a non-perturbative trans-series completion. We show how the different instanton terms `condense' at the transition point to match with the double-scaling limit trans-series. We also define a uniform large N strong-coupling expansion (a non-linear analogue of uniform WKB), which is much more precise than the conventional large N expansion through the transition region, and apply it to the evaluation of Wilson loops.

Classification of Phase Transitions by Microcanonical Inflection-Point Analysis

NASA Astrophysics Data System (ADS)

Qi, Kai; Bachmann, Michael

2018-05-01

By means of the principle of minimal sensitivity we generalize the microcanonical inflection-point analysis method by probing derivatives of the microcanonical entropy for signals of transitions in complex systems. A strategy of systematically identifying and locating independent and dependent phase transitions of any order is proposed. The power of the generalized method is demonstrated in applications to the ferromagnetic Ising model and a coarse-grained model for polymer adsorption onto a substrate. The results shed new light on the intrinsic phase structure of systems with cooperative behavior.

Squeezing via two-photon transitions

NASA Astrophysics Data System (ADS)

Savage, C. M.; Walls, D. F.

1986-05-01

The squeezing spectrum for a cavity field mode interacting with an ensemble of three-level 'Lambda-configuration' atoms by an effective two-photon transition is calculated. The advantage of the three-level Lambda system as a squeezing medium, that is, optical nonlinearity without atomic saturation, has recently been pointed out by Reid, Walls, and Dalton. Perfect squeezing is predicted at the turning points for dispersive optical bistability and good squeezing for a range of other cases. Three-level ladder atoms interacting by an effective two-photon transition are also shown to give perfect squeezing in the dispersive limit.

Problem-Solving Phase Transitions During Team Collaboration.

PubMed

Wiltshire, Travis J; Butner, Jonathan E; Fiore, Stephen M

2018-01-01

Multiple theories of problem-solving hypothesize that there are distinct qualitative phases exhibited during effective problem-solving. However, limited research has attempted to identify when transitions between phases occur. We integrate theory on collaborative problem-solving (CPS) with dynamical systems theory suggesting that when a system is undergoing a phase transition it should exhibit a peak in entropy and that entropy levels should also relate to team performance. Communications from 40 teams that collaborated on a complex problem were coded for occurrence of problem-solving processes. We applied a sliding window entropy technique to each team's communications and specified criteria for (a) identifying data points that qualify as peaks and (b) determining which peaks were robust. We used multilevel modeling, and provide a qualitative example, to evaluate whether phases exhibit distinct distributions of communication processes. We also tested whether there was a relationship between entropy values at transition points and CPS performance. We found that a proportion of entropy peaks was robust and that the relative occurrence of communication codes varied significantly across phases. Peaks in entropy thus corresponded to qualitative shifts in teams' CPS communications, providing empirical evidence that teams exhibit phase transitions during CPS. Also, lower average levels of entropy at the phase transition points predicted better CPS performance. We specify future directions to improve understanding of phase transitions during CPS, and collaborative cognition, more broadly. Copyright © 2017 Cognitive Science Society, Inc.

Aluminum oxide in stellar spectra - An infrared electronic transition

NASA Technical Reports Server (NTRS)

Luck, R. E.; Lambert, D. L.

1974-01-01

Review of recent research on the possibility of detecting the infrared electronic transition of aluminum oxide in the spectra of cool stars. It is shown that this transition may be of considerable significance for the study of Mira-type variables. Specific targets of further laboratory investigation of the transition are pointed out.

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

Here, we apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models - the square and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-one Ising (BSI) model, and the 2D XY model, and examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow exploration of different phases and symmetry-breaking, but can distinguish phase transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which ismore » particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the 'charge' correlations (vorticity) in the BSI model (XY model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the 'antoencoder method', and demonstrate that it too can be trained to capture phase transitions and critical points.« less

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

DOE PAGES

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

2017-06-19

Here, we apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models - the square and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-one Ising (BSI) model, and the 2D XY model, and examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow exploration of different phases and symmetry-breaking, but can distinguish phase transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which ismore » particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the 'charge' correlations (vorticity) in the BSI model (XY model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the 'antoencoder method', and demonstrate that it too can be trained to capture phase transitions and critical points.« less

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

NASA Astrophysics Data System (ADS)

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

2017-06-01

We apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models—the square- and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-1 Ising (BSI) model, and the two-dimensional X Y model—and we examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow the exploration of different phases and symmetry-breaking, but they can distinguish phase-transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which is particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the "charge" correlations (vorticity) in the BSI model (X Y model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the "autoencoder method," and we demonstrate that it too can be trained to capture phase transitions and critical points.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taufour, Valentin; Kaluarachchi, Udhara S.; Kogan, Vladimir G.

Here, we consider the phase diagram of a ferromagnetic system driven to a quantum phase transition with a tuning parameter $p$. Before being suppressed, the transition becomes of the first order at a tricritical point, from which wings emerge under application of the magnetic field H in the T $-$ p $-$ H phase diagram. We show that the edge of the wings merge with tangent slopes at the tricritical point.

Managing Turning Points and Transitions in Childhood and Parenthood--Insights from Families with Disabled Children in Norway

ERIC Educational Resources Information Center

Ytterhus, Borgunn; Wendelborg, Christian; Lundeby, Hege

2008-01-01

This article explores turning points and transitions emerging in the life course of children with disabilities and their parents. Through in-depth interviews with parents we found that a change appears in disabled children's social participation and belonging, at approximately eight years of age for children with learning difficulties and at…

Opportunity and Transition: Veterans Find Growth and Healing at College of Menominee Nation

ERIC Educational Resources Information Center

Benton, Sherrole

2017-01-01

The College of Menominee Nation (CMN) in Keshena, Wisconsin, is an intersection of educational services and community programs. CMN offers avenues for community members to connect in different ways. The campus can be a place of transition: a point of departure and a point of return. High school students and young adults can begin their education…

Effectively managing consumer fuel price driven transit demand.

DOT National Transportation Integrated Search

2013-05-01

This study presents a literature review of transit demand elasticities with respect to gas prices, describes features of a transit service area population that may be more sensitive to fuel prices, identifies where stress points in the family of tran...

Early warning signals for critical transitions in a thermoacoustic system

PubMed Central

Gopalakrishnan, E. A.; Sharma, Yogita; John, Tony; Dutta, Partha Sharathi; Sujith, R. I.

2016-01-01

Dynamical systems can undergo critical transitions where the system suddenly shifts from one stable state to another at a critical threshold called the tipping point. The decrease in recovery rate to equilibrium (critical slowing down) as the system approaches the tipping point can be used to identify the proximity to a critical transition. Several measures have been adopted to provide early indications of critical transitions that happen in a variety of complex systems. In this study, we use early warning indicators to predict subcritical Hopf bifurcation occurring in a thermoacoustic system by analyzing the observables from experiments and from a theoretical model. We find that the early warning measures perform as robust indicators in the presence and absence of external noise. Thus, we illustrate the applicability of these indicators in an engineering system depicting critical transitions. PMID:27767065

Organization of the Tropical Convective Cloud Population by Humidity and the Critical Transition to Heavy Precipitation

NASA Astrophysics Data System (ADS)

Igel, M.

2015-12-01

The tropical atmosphere exhibits an abrupt statistical switch between non-raining and heavily raining states as column moisture increases across a wide range of length scales. Deep convection occurs at values of column humidity above the transition point and induces drying of moist columns. With a 1km resolution, large domain cloud resolving model run in RCE, what will be made clear here for the first time is how the entire tropical convective cloud population is affected by and feeds back to the pickup in heavy precipitation. Shallow convection can act to dry the low levels through weak precipitation or vertical redistribution of moisture, or to moisten toward a transition to deep convection. It is shown that not only can deep convection dehydrate the entire column, it can also dry just the lower layer through intense rain. In the latter case, deep stratiform cloud then forms to dry the upper layer through rain with anomalously high rates for its value of column humidity until both the total column moisture falls below the critical transition point and the upper levels are cloud free. Thus, all major tropical cloud types are shown to respond strongly to the same critical phase-transition point. This mutual response represents a potentially strong organizational mechanism for convection, and the frequency of and logical rules determining physical evolutions between these convective regimes will be discussed. The precise value of the point in total column moisture at which the transition to heavy precipitation occurs is shown to result from two independent thresholds in lower-layer and upper-layer integrated humidity.

Search for Pauli exclusion principle violating atomic transitions and electron decay with a p-type point contact germanium detector

DOE PAGES

Abgrall, N.; Arnquist, I. J.; Avignone, F. T.; ...

2016-11-11

Here, a search for Pauli-exclusion-principle-violating K α electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the Kimballton Underground Research Facility. A lower limit on the transition lifetime of 5.8 × 10 30 s at 90% C.L. was set by looking for a peak at 10.6 keV resulting from the X-ray and Auger electrons present following the transition. A similar analysis was done to look for the decay of atomic K-shell electrons into neutrinos, resulting in a lower limit of 6.8 × 10 30 s at 90% C.L. Itmore » is estimated that the Majorana Demonstrator, a 44 kg array of p-type point contact detectors that will search for the neutrinoless double-beta decay of 76Ge, could improve upon these exclusion limits by an order of magnitude after three years of operation.« less

Fermion-induced quantum criticality with two length scales in Dirac systems

NASA Astrophysics Data System (ADS)

Torres, Emilio; Classen, Laura; Herbut, Igor F.; Scherer, Michael M.

2018-03-01

The quantum phase transition to a Z3-ordered Kekulé valence bond solid in two-dimensional Dirac semimetals is governed by a fermion-induced quantum critical point, which renders the putatively discontinuous transition continuous. We study the resulting universal critical behavior in terms of a functional RG approach, which gives access to the scaling behavior on the symmetry-broken side of the phase transition, for general dimensions and number of Dirac fermions. In particular, we investigate the emergence of the fermion-induced quantum critical point for spacetime dimensions 2

Faraday instability in a near-critical fluid under weightlessness.

PubMed

Gandikota, G; Chatain, D; Amiroudine, S; Lyubimova, T; Beysens, D

2014-01-01

Experiments on near-critical hydrogen have been conducted under magnetic compensation of gravity to investigate the Faraday instability that arises at the liquid-vapor interface under zero-gravity conditions. We investigated such instability in the absence of stabilizing gravity. Under such conditions, vibration orients the interface and can destabilize it. The experiments confirm the existence of Faraday waves and demonstrate a transition from a square to a line pattern close to the critical point. They also show a transition very close to the critical point from Faraday to periodic layering of the vapor-liquid interface perpendicular to vibration. It was seen that the Faraday wave instability is favored when the liquid-vapor density difference is large enough (fluid far from the critical point), whereas periodic layering predominates for small difference in the liquid and vapor densities (close to the critical point). It was observed for the Faraday wave instability that the wavelength of the instability decreases as one approaches the critical point. The experimental results demonstrate good agreement to the dispersion relation for zero gravity except for temperatures very close to the critical point where a transition from a square pattern to a line pattern is detected, similarly to what is observed under 1g conditions.

Multiple reentrant phase transitions and triple points in Lovelock thermodynamics

NASA Astrophysics Data System (ADS)

Frassino, Antonia M.; Kubizňák, David; Mann, Robert B.; Simovic, Fil

2014-09-01

We investigate the effects of higher curvature corrections from Lovelock gravity on the phase structure of asymptotically AdS black holes, treating the cosmological constant as a thermodynamic pressure. We examine how various thermodynamic phenomena, such as Van der Waals behaviour, reentrant phase transitions (RPT), and tricritical points are manifest for U(1) charged black holes in Gauss-Bonnet and 3rd-order Lovelock gravities. We furthermore observe a new phenomenon of `multiple RPT' behaviour, in which for fixed pressure the small/large/small/large black hole phase transition occurs as the temperature of the system increases. We also find that when the higher-order Lovelock couplings are related in a particular way, a peculiar isolated critical point emerges for hyperbolic black holes and is characterized by non-standard critical exponents.

Accidental degeneracy in photonic bands and topological phase transitions in two-dimensional core-shell dielectric photonic crystals.

PubMed

Xu, Lin; Wang, Hai-Xiao; Xu, Ya-Dong; Chen, Huan-Yang; Jiang, Jian-Hua

2016-08-08

A simple core-shell two-dimensional photonic crystal is studied where the triangular lattice symmetry and the C₆ point group symmetry give rich physics in accidental touching points of photonic bands. We systematically evaluate different types of accidental nodal points at the Brillouin zone center for transverse-magnetic harmonic modes when the geometry and permittivity of the core-shell material are continuously tuned. The accidental nodal points can have different dispersions and topological properties (i.e., Berry phases). These accidental nodal points can be the critical states lying between a topological phase and a normal phase of the photonic crystal. They are thus very important for the study of topological photonic states. We show that, without breaking time-reversal symmetry, by tuning the geometry of the core-shell material, a phase transition into the photonic quantum spin Hall insulator can be achieved. Here the "spin" is defined as the orbital angular momentum of a photon. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics.

Nonsymmorphic cubic Dirac point and crossed nodal rings across the ferroelectric phase transition in LiOsO3

NASA Astrophysics Data System (ADS)

Yu, Wing Chi; Zhou, Xiaoting; Chuang, Feng-Chuan; Yang, Shengyuan A.; Lin, Hsin; Bansil, Arun

2018-05-01

Crystalline symmetries can generate exotic band-crossing features, which can lead to unconventional fermionic excitations with interesting physical properties. We show how a cubic Dirac point—a fourfold-degenerate band-crossing point with cubic dispersion in a plane and a linear dispersion in the third direction—can be stabilized through the presence of a nonsymmorphic glide mirror symmetry in the space group of the crystal. Notably, the cubic Dirac point in our case appears on a threefold axis, even though it has been believed previously that such a point can only appear on a sixfold axis. We show that a cubic Dirac point involving a threefold axis can be realized close to the Fermi level in the nonferroelectric phase of LiOsO3. Upon lowering temperature, LiOsO3 has been shown experimentally to undergo a structural phase transition from the nonferroelectric phase to the ferroelectric phase with spontaneously broken inversion symmetry. Remarkably, we find that the broken symmetry transforms the cubic Dirac point into three mutually crossed nodal rings. There also exist several linear Dirac points in the low-energy band structure of LiOsO3, each of which is transformed into a single nodal ring across the phase transition.

Accounting for professionalism: an innovative point system to assess resident professionalism.

PubMed

Malakoff, Gary L; Payne, Catherine L; Staton, Lisa J; Kolade, Victor O; Panda, Mukta

2014-01-01

Professionalism is a core competency for residency required by the Accreditation Council of Graduate Medical Education. We sought a means to objectively assess professionalism among internal medicine and transitional year residents. We established a point system to document unprofessional behaviors demonstrated by internal medicine and transitional year residents along with opportunities to redeem such negative points by deliberate positive professional acts. The intent of the policy is to assist residents in becoming aware of what constitutes unprofessional behavior and to provide opportunities for remediation by accruing positive points. A committee of core faculty and department leadership including the program director and clinic nurse manager determines professionalism points assigned. Negative points might be awarded for tardiness to mandatory or volunteered for events without a valid excuse, late evaluations or other paperwork required by the department, non-attendance at meetings prepaid by the department, and inappropriate use of personal days or leave. Examples of actions through which positive points can be gained to erase negative points include delivery of a mentored pre-conference talk, noon conference, medical student case/shelf review session, or a written reflection. Between 2009 and 2012, 83 residents have trained in our program. Seventeen categorical internal medicine and two transitional year residents have been assigned points. A total of 55 negative points have been assigned and 19 points have been remediated. There appears to be a trend of fewer negative points and more positive points being assigned over each of the past three academic years. Commitment to personal professional behavior is a lifelong process that residents must commit to during their training. A professionalism policy, which employs a point system, has been instituted in our programs and may be a novel tool to promote awareness and underscore the merits of the professionalism competency.

Magnetic-field induced quantum critical points of valence transition in Ce- and Yb-based heavy fermions

NASA Astrophysics Data System (ADS)

Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques

2009-03-01

Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn5 and metamagnetic transition in YbXCu4 for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL100, (2008) 236401.

"Trying to Push Things through": Forms and Bounds of Agency in Transitions of School-Age Young People

ERIC Educational Resources Information Center

Aaltonen, Sanna

2013-01-01

The conventional approach to youth transitions has focused on particular transitional points taking place after the completion of compulsory education. This paper focuses on the ways in which institutional regulations, individual agency, and emotions are related in bringing about such significant transitions that take place outside the traditional…

Phases of higher spin black holes: Hawking-Page, transitions between black holes, and a critical point

NASA Astrophysics Data System (ADS)

Bañados, Máximo; Düring, Gustavo; Faraggi, Alberto; Reyes, Ignacio A.

2017-08-01

We study the thermodynamic phase diagram of three-dimensional s l (N ;R ) higher spin black holes. By analyzing the semiclassical partition function we uncover a rich structure that includes Hawking-Page transitions to the AdS3 vacuum, first order phase transitions among black hole states, and a second order critical point. Our analysis is explicit for N =4 but we extrapolate some of our conclusions to arbitrary N . In particular, we argue that even N is stable in the ensemble under consideration but odd N is not.

Motion transitions of falling plates via quasisteady aerodynamics.

PubMed

Hu, Ruifeng; Wang, Lifeng

2014-07-01

In this paper, we study the dynamics of freely falling plates based on the Kirchhoff equation and the quasisteady aerodynamic model. Motion transitions among fluttering, tumbling along a cusp-like trajectory, irregular, and tumbling along a straight trajectory are obtained by solving the dynamical equations. Phase diagrams spanning between the nondimensional moment of inertia and aerodynamic coefficients or aspect ratio are built to identify regimes for these falling styles. We also investigate the stability of fixed points and bifurcation scenarios. It is found that the transitions are all heteroclinic bifurcations and the influence of the fixed-point stability is local.

Ground-state fidelity and bipartite entanglement in the Bose-Hubbard model.

PubMed

Buonsante, P; Vezzani, A

2007-03-16

We analyze the quantum phase transition in the Bose-Hubbard model borrowing two tools from quantum-information theory, i.e., the ground-state fidelity and entanglement measures. We consider systems at unitary filling comprising up to 50 sites and show for the first time that a finite-size scaling analysis of these quantities provides excellent estimates for the quantum critical point. We conclude that fidelity is particularly suited for revealing a quantum phase transition and pinning down the critical point thereof, while the success of entanglement measures depends on the mechanisms governing the transition.

Polaronic and dressed molecular states in orbital Feshbach resonances

NASA Astrophysics Data System (ADS)

Xu, Junjun; Qi, Ran

2018-04-01

We consider the impurity problem in an orbital Feshbach resonance (OFR), with a single excited clock state | e ↑⟩ atom immersed in a Fermi sea of electronic ground state | g ↓⟩. We calculate the polaron effective mass and quasi-particle residue, as well as the polaron to molecule transition. By including one particle-hole excitation in the molecular state, we find significant correction to the transition point. This transition point moves toward the BCS side for increasing particle densities, which suggests that the corresponding many-body physics is similar to a narrow resonance.

Applying threshold concepts to conservation management of dryland ecosystems: Case studies on the Colorado Plateau

USGS Publications Warehouse

Bowker, Matthew A.; Miller, Mark E.; Garman, Steven L.; Belote, Travis; Guntenspergen, Glenn R.

2014-01-01

Ecosystems may occupy functionally distinct alternative states, some of which are more or less desirable from a management standpoint. Transitions from state to state are usually associated with a particular trigger or sequence of triggers, such as the addition or subtraction of a disturbance. Transitions are often not linear, rather it is common to see an abrupt transition come about even though the trigger increases only incrementally; these are examples of threshold behaviors. An ideal monitoring program, such as the National Park Service’s Inventory and Monitoring Program, would quantify triggers, and be able to inform managers when measurements of a trigger are approaching a threshold so that management action can avoid an unwanted state transition. Unfortunately, both triggers and the threshold points at which state transitions occur are generally only partially known. Using case studies, we advance a general procedure to help identify triggers and estimate where threshold dynamics may occur. Our procedure is as follows: (1) Operationally define the ecosystem type being considered; we suggest that the ecological site concept of the Natural Resource Conservation Service is a useful system, (2) Using all available a priori knowledge to develop a state-and-transition model (STM), which defines possible ecosystem states, plausible transitions among them and likely triggers, (3) Validate the STM by verifying the existence of its states to the greatest degree possible, (4) Use the STM model to identify transitions and triggers likely to be detectable by a monitoring program, and estimate to the greatest degree possible the value of a measurable indicator of a trigger at the point that a state transition is imminent (tipping point), and values that may indicate when management intervention should be considered (assessment points). We illustrate two different methods for attaining these goals using a data-rich case study in Canyonlands National Park, and a data-poor case study in Wupatki National Monument. In the data-rich case, STMs are validated and revised, and tipping and assessment points are estimated using statistical analysis of data. In the data-poor case, we develop an iterative expert opinion survey approach to validate the degree of confidence in an STM, revise the model, identify lack of confidence in specific model components, and create reasonable first approximations of tipping and assessment points, which can later be refined when more data are available. Our goal should be to develop the best set of models possible given the level of information available to support decisions, which is often not much. The approach presented here offers a flexible means of achieving this goal, and determining specific research areas in need of study.

Resilience of Greek Youth at an Educational Transition Point: The Role of Locus of Control and Coping Strategies as Resources

ERIC Educational Resources Information Center

Leontopoulou, Sophia

2006-01-01

Variable--and person--focused approaches were applied to study the resilient outcomes of 326 Greek male and female 1st year university students at a major educational transition point. Results indicated that resilience was related to both cognitive and behavioural psychosocial resources in late adolescence. Locus of control emerged as an important…

Distinguishing 6 Population Subgroups by Timing and Characteristics of the Menopausal Transition

PubMed Central

Huang, Xiaobi; Harlow, Siobán D.; Elliott, Michael R.

2012-01-01

Changes in women’s menstrual bleeding patterns precede the onset of menopause. In this paper, the authors identify population subgroups based on menstrual characteristics of the menopausal transition experience. Using the TREMIN data set (1943–1979), the authors apply a Bayesian change-point model with 8 parameters for each woman that summarize change in menstrual bleeding patterns during the menopausal transition. The authors then use estimates from this model to classify menstrual patterns into subgroups using a K-medoids algorithm. They identify 6 subgroups of women whose transition experience can be distinguished by age at onset, variability of the menstrual cycle, and duration of the early transition. These results suggest that for most women, mean and variance change points are well aligned with proposed bleeding markers of the menopausal transition, but for some women they are not clearly associated. Increasing understanding of population differences in the transition experience may lead to new insights into ovarian aging. Because of age inclusion criteria, most longitudinal studies of the menopausal transition probably include only a subset of the 6 subgroups of women identified in this paper, suggesting a potential bias in the understanding of both the menopausal transition and the linkage between the transition and chronic disease. PMID:22138039

Laser-Induced Melting of Co-C Eutectic Cells as a New Research Tool

NASA Astrophysics Data System (ADS)

van der Ham, E.; Ballico, M.; Jahan, F.

2015-08-01

A new laser-based technique to examine heat transfer and energetics of phase transitions in metal-carbon fixed points and potentially to improve the quality of phase transitions in furnaces with poor uniformity is reported. Being reproducible below 0.1 K, metal-carbon fixed points are increasingly used as reference standards for the calibration of thermocouples and radiation thermometers. At NMIA, the Co-C eutectic point is used for the calibration of thermocouples, with the fixed point traceable to the International Temperature Scale (ITS-90) using radiation thermometry. For thermocouple use, these cells are deep inside a high-uniformity furnace, easily obtaining excellent melting plateaus. However, when used with radiation thermometers, the essential large viewing cone to the crucible restricts the furnace depth and introduces large heat losses from the front furnace zone, affecting the quality of the phase transition. Short laser bursts have been used to illuminate the cavity of a conventional Co-C fixed-point cell during various points in its melting phase transition. The laser is employed to partially melt the metal at the rear of the crucible providing a liquid-solid interface close to the region being observed by the reference pyrometer. As the laser power is known, a quantitative estimate of can be made for the Co-C latent heat of fusion. Using a single laser pulse during a furnace-induced melt, a plateau up to 8 min is observed before the crucible resumes a characteristic conventional melt curve. Although this plateau is satisfyingly flat, well within 100 mK, it is observed that the plateau is laser energy dependent and elevates from the conventional melt "inflection-point" value.

The α-γ-ɛ triple point and phase boundaries of iron under shock compression

NASA Astrophysics Data System (ADS)

Li, Jun; Wu, Qiang; Xue, Tao; Geng, Huayun; Yu, Jidong; Jin, Ke; Li, Jiabo; Tan, Ye; Xi, Feng

2017-07-01

The phase transition of iron under shock compression has attracted much attention in recent decades because of its importance in fields such as condensed matter physics, geophysics, and metallurgy. At room temperature, the transition of iron from the α-phase (bcc) to the ɛ-phase (hpc) occurs at a stress of 13 GPa. At high temperature, a triple point followed by transformation to the γ-phase (fcc) is expected. However, the details of the high-temperature phase transitions of iron are still under debate. Here, we investigate the phase-transition behavior of polycrystalline iron under compression from room temperature to 820 K. The results show that the shock-induced phase transition is determined unequivocally from the measured three-wave-structure profiles, which clearly consist of an elastic wave, a plastic wave, and a phase-transition wave. The phase transition is temperature-dependent, with an average rate Δσtr/ΔT of -6.91 MPa/K below 700 K and -34.7 MPa/K at higher temperatures. The shock α-ɛ and α-γ phase boundaries intersect at 10.6 ± 0.53 GPa and 763 K, which agrees with the α-ɛ-γ triple point from early shock wave experiments and recent laser-heated diamond-anvil cell resistivity and in situ X-ray diffraction data but disagrees with the shock pressure-temperature phase diagram reported in 2009 by Zaretsky [J. Appl. Phys. 106, 023510 (2009)].

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaluarachchi, Udhara S.; Taufour, Valentin; Bud'ko, Sergey L.

We report the temperature-pressure-magnetic eld phase diagram of the ferromagnetic Kondolattice CeTiGe 3 determined by means of electrical resistivity measurements. Measurements up to ~5.8GPa reveal a rich phase diagram with multiple phase transitions. At ambient pressure, CeTiGe 3 orders ferromagnetically at T C =14 K. Application of pressure suppresses T C, but a pressure induced ferromagnetic quantum criticality is avoided by the appearance of two new successive transitions for p>4.1GPa that are probably antiferromagnetic in nature. These two transitions are suppressed under pressure, with the lower temperature phase being fully suppressed above 5.3GPa. The critical pressures for the presumed quantummore » phase transitions are p1≅4.1GPa and p2≅5.3GPa. Above 4.1GPa, application of magnetic eld shows a tricritical point evolving into a wing structure phase with a quantum tricritical point at 2.8T at 5.4GPa, where the rst order antiferromagneticferromagnetic transition changes into the second order antiferromagnetic-ferromagnetic transition.« less

Robustness of critical points in a complex adaptive system: Effects of hedge behavior

NASA Astrophysics Data System (ADS)

Liang, Yuan; Huang, Ji-Ping

2013-08-01

In our recent papers, we have identified a class of phase transitions in the market-directed resource-allocation game, and found that there exists a critical point at which the phase transitions occur. The critical point is given by a certain resource ratio. Here, by performing computer simulations and theoretical analysis, we report that the critical point is robust against various kinds of human hedge behavior where the numbers of herds and contrarians can be varied widely. This means that the critical point can be independent of the total number of participants composed of normal agents, herds and contrarians, under some conditions. This finding means that the critical points we identified in this complex adaptive system (with adaptive agents) may also be an intensive quantity, similar to those revealed in traditional physical systems (with non-adaptive units).

Method for contour extraction for object representation

DOEpatents

Skourikhine, Alexei N.; Prasad, Lakshman

2005-08-30

Contours are extracted for representing a pixelated object in a background pixel field. An object pixel is located that is the start of a new contour for the object and identifying that pixel as the first pixel of the new contour. A first contour point is then located on the mid-point of a transition edge of the first pixel. A tracing direction from the first contour point is determined for tracing the new contour. Contour points on mid-points of pixel transition edges are sequentially located along the tracing direction until the first contour point is again encountered to complete tracing the new contour. The new contour is then added to a list of extracted contours that represent the object. The contour extraction process associates regions and contours by labeling all the contours belonging to the same object with the same label.

From the granular Leidenfrost state to buoyancy-driven convection.

PubMed

Rivas, Nicolas; Thornton, Anthony R; Luding, Stefan; van der Meer, Devaraj

2015-04-01

Grains inside a vertically vibrated box undergo a transition from a density-inverted and horizontally homogeneous state, referred to as the granular Leidenfrost state, to a buoyancy-driven convective state. We perform a simulational study of the precursors of such a transition and quantify their dynamics as the bed of grains is progressively fluidized. The transition is preceded by transient convective states, which increase their correlation time as the transition point is approached. Increasingly correlated convective flows lead to density fluctuations, as quantified by the structure factor, that also shows critical behavior near the transition point. The amplitude of the modulations in the vertical velocity field are seen to be best described by a quintic supercritical amplitude equation with an additive noise term. The validity of such an amplitude equation, and previously observed collective semiperiodic oscillations of the bed of grains, suggests a new interpretation of the transition analogous to a coupled chain of vertically vibrated damped oscillators. Increasing the size of the container shows metastability of convective states, as well as an overall invariant critical behavior close to the transition.

Glassy behavior and dynamic tweed in defect-free multiferroics

NASA Astrophysics Data System (ADS)

Wang, Xiaofei; Salje, Ekhard K. H.; Sun, Jun; Ding, Xiangdong

2018-01-01

Multiferroics often show significant elastic fluctuations even when the transition is strongly stepwise. Molecular dynamics simulations of a generic toy model show the appearance of tweed nanostructures (cross hatched patterns) in the paraelastic phase just above the transition point. This tweed lowers the elastic modulus C12 when approaching the transition temperature. The spatial and temporal correlations of the tweed structure follow the Vogel-Fulcher relationship, and the Vogel-Fulcher temperature is slightly below the transition temperature Ttrans, preventing this glassy state to freeze completely. Spatial correlations of shear strain show that the size of tweed patches reaches about eight lattice spacings near Ttrans. Cross- and rod-shaped diffuse scattering, similar to that in relaxors, emerges around {hh0}* and {h00}* Bragg reflections. The viscosity of the sample increases dramatically at the transition point with a significant precursor increase in the tweed regime.

A preliminary investigation of boundary-layer transition along a flat plate with adverse pressure gradient

NASA Technical Reports Server (NTRS)

Von Doenhoff, Albert E

1938-01-01

Boundary-layer surveys were made throughout the transition region along a smooth flat plate placed in an airstream of practically zero turbulence and with an adverse pressure gradient. The boundary-layer Reynolds number at the laminar separation point was varied from 1,800 to 2,600. The test data, when considered in the light of certain theoretical deductions, indicated that transition probably began with separation of the laminar boundary layer. The extent of the transition region, defined as the distance from a calculated laminar separation point to the position of the first fully developed turbulent boundary-layer profile, could be expressed as a constant Reynolds number run of approximately 70,000. Some speculations are presented concerning the application of the foregoing concepts, after certain assumptions have been made, to the problem of the connection between transition on the upper surface of an airfoil at high angles of attack and the maximum lift.

A Bayesian Interpretation of First-Order Phase Transitions

NASA Astrophysics Data System (ADS)

Davis, Sergio; Peralta, Joaquín; Navarrete, Yasmín; González, Diego; Gutiérrez, Gonzalo

2016-03-01

In this work we review the formalism used in describing the thermodynamics of first-order phase transitions from the point of view of maximum entropy inference. We present the concepts of transition temperature, latent heat and entropy difference between phases as emergent from the more fundamental concept of internal energy, after a statistical inference analysis. We explicitly demonstrate this point of view by making inferences on a simple game, resulting in the same formalism as in thermodynamical phase transitions. We show that analogous quantities will inevitably arise in any problem of inferring the result of a yes/no question, given two different states of knowledge and information in the form of expectation values. This exposition may help to clarify the role of these thermodynamical quantities in the context of different first-order phase transitions such as the case of magnetic Hamiltonians (e.g. the Potts model).

Nonequilibrium Second-Order Phase Transition in a Cooper-Pair Insulator.

PubMed

Doron, A; Tamir, I; Mitra, S; Zeltzer, G; Ovadia, M; Shahar, D

2016-02-05

In certain disordered superconductors, upon increasing the magnetic field, superconductivity terminates with a direct transition into an insulating phase. This phase is comprised of localized Cooper pairs and is termed a Cooper-pair insulator. The current-voltage characteristics measured in this insulating phase are highly nonlinear and, at low temperatures, exhibit abrupt current jumps. Increasing the temperature diminishes the jumps until the current-voltage characteristics become continuous. We show that a direct correspondence exists between our system and systems that undergo an equilibrium, second-order, phase transition. We illustrate this correspondence by comparing our results to the van der Waals equation of state for the liquid-gas mixture. We use the similarities to identify a critical point where an out of equilibrium second-order-like phase transition occurs in our system. Approaching the critical point, we find a power-law behavior with critical exponents that characterizes the transition.

Instability of Insulators near Quantum Phase Transitions

NASA Astrophysics Data System (ADS)

Doron, A.; Tamir, I.; Levinson, T.; Ovadia, M.; Sacépé, B.; Shahar, D.

2017-12-01

Thin films of amorphous indium oxide undergo a magnetic field driven superconducting to insulator quantum phase transition. In the insulating phase, the current-voltage characteristics show large current discontinuities due to overheating of electrons. We show that the onset voltage for the discontinuities vanishes as we approach the quantum critical point. As a result, the insulating phase becomes unstable with respect to any applied voltage making it, at least experimentally, immeasurable. We emphasize that unlike previous reports of the absence of linear response near quantum phase transitions, in our system, the departure from equilibrium is discontinuous. Because the conditions for these discontinuities are satisfied in most insulators at low temperatures, and due to the decay of all characteristic energy scales near quantum phase transitions, we believe that this instability is general and should occur in various systems while approaching their quantum critical point. Accounting for this instability is crucial for determining the critical behavior of systems near the transition.

Quantum phase transition from mixed atom-molecule phase to pure molecule phase: Characteristic scaling laws and Berry-curvature signature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Shengchang; Graduate School, China Academy of Engineering Physics, Beijing 100088; Fu Libin

2011-08-15

We investigate the quantum phase transition in an ultracold atom-molecule conversion system. It is found that the system undergoes a phase transition from a mixed atom-molecule phase to a pure molecule phase when the energy bias exceeds a critical value. By constructing a coherent state as variational state, we get a good approximation of the quantum ground state of the system. Using this variational state, we deduce the critical point analytically. We then discuss the scaling laws characterizing the transition and obtain the corresponding critical exponents. Furthermore, the Berry curvature signature of the transition is studied. In particular, we findmore » that the derivatives of the Berry curvature with respect to total particle number intersect at the critical point. The underlying mechanism of this finding is discussed as well.« less

Anomalous critical behavior in the polymer collapse transition of three-dimensional lattice trails.

PubMed

Bedini, Andrea; Owczarek, Aleksander L; Prellberg, Thomas

2012-07-01

Trails (bond-avoiding walks) provide an alternative lattice model of polymers to self-avoiding walks, and adding self-interaction at multiply visited sites gives a model of polymer collapse. Recently a two-dimensional model (triangular lattice) where doubly and triply visited sites are given different weights was shown to display a rich phase diagram with first- and second-order collapse separated by a multicritical point. A kinetic growth process of trails (KGTs) was conjectured to map precisely to this multicritical point. Two types of low-temperature phases, a globule phase and a maximally dense phase, were encountered. Here we investigate the collapse properties of a similar extended model of interacting lattice trails on the simple cubic lattice with separate weights for doubly and triply visited sites. Again we find first- and second-order collapse transitions dependent on the relative sizes of the doubly and triply visited energies. However, we find no evidence of a low-temperature maximally dense phase with only the globular phase in existence. Intriguingly, when the ratio of the energies is precisely that which separates the first-order from the second-order regions anomalous finite-size scaling appears. At the finite-size location of the rounded transition clear evidence exists for a first-order transition that persists in the thermodynamic limit. This location moves as the length increases, with its limit apparently at the point that maps to a KGT. However, if one fixes the temperature to sit at exactly this KGT point, then only a critical point can be deduced from the data. The resolution of this apparent contradiction lies in the breaking of crossover scaling and the difference in the shift and transition width (crossover) exponents.

Quantum multicriticality in disordered Weyl semimetals

NASA Astrophysics Data System (ADS)

Luo, Xunlong; Xu, Baolong; Ohtsuki, Tomi; Shindou, Ryuichi

2018-01-01

In electronic band structure of solid-state material, two band-touching points with linear dispersion appear in pairs in the momentum space. When they annihilate each other, the system undergoes a quantum phase transition from a three-dimensional (3D) Weyl semimetal (WSM) phase to a band insulator phase such as a Chern band insulator (CI) phase. The phase transition is described by a new critical theory with a "magnetic dipole"-like object in the momentum space. In this paper, we reveal that the critical theory hosts a novel disorder-driven quantum multicritical point, which is encompassed by three quantum phases: a renormalized WSM phase, a CI phase, and a diffusive metal (DM) phase. Based on the renormalization group argument, we first clarify scaling properties around the band-touching points at the quantum multicritical point as well as all phase boundaries among these three phases. Based on numerical calculations of localization length, density of states, and critical conductance distribution, we next prove that a localization-delocalization transition between the CI phase with a finite zero-energy density of states (zDOS) and DM phase belongs to an ordinary 3D unitary class. Meanwhile, a localization-delocalization transition between the Chern insulator phase with zero zDOS and a renormalized WSM phase turns out to be a direct phase transition whose critical exponent ν =0.80 ±0.01 . We interpret these numerical results by a renormalization group analysis on the critical theory.

Tricritical point of the f -electron antiferromagnet US b 2 driven by high magnetic fields

DOE PAGES

Stillwell, R. L.; Liu, I. -L.; Harrison, Neil; ...

2017-01-12

In pulsed magnetic fields up to 65 T and at temperatures below the Néel transition, our magnetization and magnetostriction measurements reveal a field-induced metamagneticlike transition that is suggestive of an antiferromagnetic to ferrimagnetic ordering. Our data also suggest a change in the nature of this metamagneticlike transition from second- to first-order-like near a tricritical point at T tc ~ 145K and H c ~ 52 T. At high fields for H > H c we found a decreased magnetic moment roughly half of the moment determined by neutron powder diffraction. Lastly, we propose that the decreased moment and lack ofmore » saturation at high fields indicate the presence of a field-induced ferrimagnetic state above the tricritical point of the H-T phase diagram for USb 2.« less

Analysis of the thermal expansivity near the tricritical point in dilute chromium alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yurtseven, H., E-mail: hamit@metu.edu.tr; Tari, Ö., E-mail: ozlemilgin@arel.edu.tr

Chromium (Cr) undergoes a first order Neel transition as an antiferromagnetic material. When V, Mo and Mn atoms are substituted in the Cr lattice, a weak first order Neel transition in pure Cr changes toward a second order transition and a possible tricritical point in CrV occurs close to 0.2 at %V, as observed experimentally from the measurements of the thermal expansivity at various temperatures. In this study, we analyze the experimental data for the thermal expansivity from the literature as a function of temperature using the power - law formula for Cr alloys (Cr - 0.1V, 0.2V, 0.5V andmore » Cr - 0.1Mn, Cr - 0.2Mo, 0.3Mo, 0.4Mo). Our results are interpreted near the tricritical point in dilute chromium alloys.« less

Quantum criticality and first-order transitions in the extended periodic Anderson model

NASA Astrophysics Data System (ADS)

Hagymási, I.; Itai, K.; Sólyom, J.

2013-03-01

We investigate the behavior of the periodic Anderson model in the presence of d-f Coulomb interaction (Udf) using mean-field theory, variational calculation, and exact diagonalization of finite chains. The variational approach based on the Gutzwiller trial wave function gives a critical value of Udf and two quantum critical points (QCPs), where the valence susceptibility diverges. We derive the critical exponent for the valence susceptibility and investigate how the position of the QCP depends on the other parameters of the Hamiltonian. For larger values of Udf, the Kondo regime is bounded by two first-order transitions. These first-order transitions merge into a triple point at a certain value of Udf. For even larger Udf valence skipping occurs. Although the other methods do not give a critical point, they support this scenario.

Magnification of signatures of a topological phase transition by quantum zero point motion

NASA Astrophysics Data System (ADS)

Lopes, Pedro L. e. S.; Ghaemi, Pouyan

2015-08-01

We show that the zero point motion of a vortex in superconducting doped topological insulators leads to significant changes in the electronic spectrum at the topological phase transition in this system. This topological phase transition is tuned by the doping level, and the corresponding effects are manifest in the density of states at energies which are on the order of the vortex fluctuation frequency. Although the electronic energy gap in the spectrum generated by a stationary vortex is but a small fraction of the bulk superconducting gap, the vortex fluctuation frequency may be much larger. As a result, this quantum zero point motion can induce a discontinuous change in the spectral features of the system at the topological vortex phase transition to energies which are well within the resolution of scanning tunneling microscopy. This discontinuous change is exclusive to superconducting systems in which we have a topological phase transition. Moreover, the phenomena studied in this paper present effects of Magnus forces on the vortex spectrum which are not present in the ordinary s -wave superconductors. Finally, we demonstrate explicitly that the vortex in this system is equivalent to a Kitaev chain. This allows for the mapping of the vortex fluctuating scenario in three dimensions into similar one-dimensional situations in which one may search for other novel signatures of topological phase transitions.

Accessing the exceptional points of parity-time symmetric acoustics

PubMed Central

Shi, Chengzhi; Dubois, Marc; Chen, Yun; Cheng, Lei; Ramezani, Hamidreza; Wang, Yuan; Zhang, Xiang

2016-01-01

Parity-time (PT) symmetric systems experience phase transition between PT exact and broken phases at exceptional point. These PT phase transitions contribute significantly to the design of single mode lasers, coherent perfect absorbers, isolators, and diodes. However, such exceptional points are extremely difficult to access in practice because of the dispersive behaviour of most loss and gain materials required in PT symmetric systems. Here we introduce a method to systematically tame these exceptional points and control PT phases. Our experimental demonstration hinges on an active acoustic element that realizes a complex-valued potential and simultaneously controls the multiple interference in the structure. The manipulation of exceptional points offers new routes to broaden applications for PT symmetric physics in acoustics, optics, microwaves and electronics, which are essential for sensing, communication and imaging. PMID:27025443

Momentum-dependent hybridization gap and dispersive in-gap state of the Kondo semiconductor SmB6

NASA Astrophysics Data System (ADS)

Miyazaki, Hidetoshi; Hajiri, Tetsuya; Ito, Takahiro; Kunii, Satoru; Kimura, Shin-ichi

2012-08-01

We report the temperature-dependent three-dimensional angle-resolved photoemission spectra of the Kondo semiconductor SmB6. We found a difference in the temperature dependence of the peaks at the X and Γ points, due to hybridization between the Sm 5d conduction band and the nearly localized Sm 4f state. The peak intensity at the X point has the same temperature dependence as the valence transition below 120 K, while that at the Γ point is consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This suggests that the hybridization with the valence transition mainly occurs near the X point, and the initial state of the magnetic excitation is located near the Γ point.

The Department of Defense Shale Oil Task Force. Volume I.

DTIC Science & Technology

1978-10-05

transition from natural crude to synthetic fuels during the time period 1985-2010. The report also points out that shale-derived military mobility fuel is...transition from natural crude to synthetic fuels during the time period 1985-201)1. The report also points out that shale-derived military mobility...with emphasis on comparative economics, environmental and timing considerations. o Industrial considerations. o Research and development on new

Thermodynamic Vortex-Lattice Phase Transitions in Bi_2Sr_2CaCu_2O_8

NASA Astrophysics Data System (ADS)

Majer, Daniel

1996-03-01

Recent measurements by the microscopic Hall-sensor arrays technique of the anomalous second magnetization peak and the magnetization step at the first-order transition in Bi_2Sr_2CaCu_2O8 (BSCCO)(B. Khaykovich, E. Zeldov, D. Majer, T.W. Li, P.H. Kes, and M. Konczykowski, (preprint).) have revealed new evidence, which suggest that these two phenomena are of related origin. The first-order transition(E. Zeldov, D. Majer, M. Konczykowski, V.B. Geshkenbein, V.M. Vinokur, and H. Shtrikman, Nature 375), 373 (1995). at higher temperatures ends at a critical point and it seems that a second-order transition (the fish-tail) continues to lower temperatures. Local magnetization measurements were carried out on several as-grown BSCCO crystals (T_c~= 90 K) and on two crystals annealed in air at 500^circC (over-doped with T_c~= 83.5 K) and at 800^circC (optimally-doped, T_c~= 89 K). The annealing was used to change the oxygen stoichiometry of the crystals and as a consequence their anisotropy. All as-grown crystals from two sources show practically identical phase diagrams. The first-order phase transition lines in the B-T phase diagram of the annealed crystals however, are shifted significantly. In the over-doped crystal the line is shifted to higher fields, and the optimally-doped crystal to lower fields as compared to the as-grown crystals. Theoretical predictions of both the melting and the decoupling transitions in HTSC are anisotropy dependent, and the observed shifts can not be used to distinguish between these theories. However, the temperature dependence of the transition line in the decoupling scenario fits the observed data much better than the melting scenario. The first-order transition step vanishes in all three types of crystals at a critical point which is anisotropy dependent. At lower temperatures the second magnetization peak is observed. The second peak line in the B-T phase diagram of all the crystals measured starts very close to the critical point and is shifted by the same extent as the corresponding first-order transition line. The two lines seem to form one continuous phase transition line that changes from first-order to presumably second-order at the critical point. In collaboration with B. Khaykovich, T.W. Li, P.H. Kes, M. Konczykowski, and E. Zeldov.

Trapping Phenomenon Attenuates the Consequences of Tipping Points for Limit Cycles

NASA Astrophysics Data System (ADS)

Medeiros, Everton S.; Caldas, Iberê L.; Baptista, Murilo S.; Feudel, Ulrike

2017-02-01

Nonlinear dynamical systems may be exposed to tipping points, critical thresholds at which small changes in the external inputs or in the system’s parameters abruptly shift the system to an alternative state with a contrasting dynamical behavior. While tipping in a fold bifurcation of an equilibrium is well understood, much less is known about tipping of oscillations (limit cycles) though this dynamics are the typical response of many natural systems to a periodic external forcing, like e.g. seasonal forcing in ecology and climate sciences. We provide a detailed analysis of tipping phenomena in periodically forced systems and show that, when limit cycles are considered, a transient structure, so-called channel, plays a fundamental role in the transition. Specifically, we demonstrate that trajectories crossing such channel conserve, for a characteristic time, the twisting behavior of the stable limit cycle destroyed in the fold bifurcation of cycles. As a consequence, this channel acts like a “ghost” of the limit cycle destroyed in the critical transition and instead of the expected abrupt transition we find a smooth one. This smoothness is also the reason that it is difficult to precisely determine the transition point employing the usual indicators of tipping points, like critical slowing down and flickering.

50 CFR 14.14 - In-transit shipments.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., POSSESSION, TRANSPORTATION, SALE, PURCHASE, BARTER, EXPORTATION, AND IMPORTATION OF WILDLIFE AND PLANTS....14 In-transit shipments. (a) Wildlife destined for a point within the United States may be imported...

An empirical model for the complex dielectric permittivity of soils as a function of water content

NASA Technical Reports Server (NTRS)

Wang, J. R.; Chmugge, T. J.

1978-01-01

The recent measurements on the dielectric properties of soils shows that the variation of dielectric constant with moisture content depends on soil types. The observed dielectric constant increases only slowly with moisture content up to a transition point. Beyond the transition it increases rapidly with moisture content. The moisture value of transition region was found to be higher for high clay content soils than for sandy soils. Many mixing formulas were compared with, and were found incompatible with, the measured dielectric variations of soil-water mixtures. A simple empirical model was proposed to describe the dielectric behavior of ths soil-water mixtures. The relationship between transition moisture and wilting point provides a means of estimating soil dielectric properties on the basis of texture information.

Quantum Griffiths singularity of superconductor-metal transition in Ga thin films.

PubMed

Xing, Ying; Zhang, Hui-Min; Fu, Hai-Long; Liu, Haiwen; Sun, Yi; Peng, Jun-Ping; Wang, Fa; Lin, Xi; Ma, Xu-Cun; Xue, Qi-Kun; Wang, Jian; Xie, X C

2015-10-30

The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions. Copyright © 2015, American Association for the Advancement of Science.

Transition probability, dynamic regimes, and the critical point of financial crisis

NASA Astrophysics Data System (ADS)

Tang, Yinan; Chen, Ping

2015-07-01

An empirical and theoretical analysis of financial crises is conducted based on statistical mechanics in non-equilibrium physics. The transition probability provides a new tool for diagnosing a changing market. Both calm and turbulent markets can be described by the birth-death process for price movements driven by identical agents. The transition probability in a time window can be estimated from stock market indexes. Positive and negative feedback trading behaviors can be revealed by the upper and lower curves in transition probability. Three dynamic regimes are discovered from two time periods including linear, quasi-linear, and nonlinear patterns. There is a clear link between liberalization policy and market nonlinearity. Numerical estimation of a market turning point is close to the historical event of the US 2008 financial crisis.

Quantum phase transitions in a two-dimensional quantum XYX model: ground-state fidelity and entanglement.

PubMed

Li, Bo; Li, Sheng-Hao; Zhou, Huan-Qiang

2009-06-01

A systematic analysis is performed for quantum phase transitions in a two-dimensional anisotropic spin-1/2 antiferromagnetic XYX model in an external magnetic field. With the help of an innovative tensor network algorithm, we compute the fidelity per lattice site to demonstrate that the field-induced quantum phase transition is unambiguously characterized by a pinch point on the fidelity surface, marking a continuous phase transition. We also compute an entanglement estimator, defined as a ratio between the one-tangle and the sum of squared concurrences, to identify both the factorizing field and the critical point, resulting in a quantitative agreement with quantum Monte Carlo simulation. In addition, the local order parameter is "derived" from the tensor network representation of the system's ground-state wave functions.

A Search for Lost Planets in the Kepler Multi-planet Systems and the Discovery of the Long-period, Neptune-sized Exoplanet Kepler-150 f

NASA Astrophysics Data System (ADS)

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2017-04-01

The vast majority of the 4700 confirmed planets (CPs) and planet candidates discovered by the Kepler mission were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a “Swiss cheese”-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or “lost”). We examine a sample of 114 stars with 3+ CPs to evaluate the effect of this “Swiss cheesing.” A simulation determines that the probability that a transiting planet is lost due to the transit masking is low, but non-negligible, reaching a plateau at ˜3.3% lost in the period range of P = 400-500 days. We then model all planet transits and subtract out the transit signals for each star, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (I.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline’s choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet (Kepler-150 f) and a potential single transit of a likely false positive (FP) (Kepler-208). Kepler-150 f (P = 637.2 days, {R}{{P}}={3.64}-0.39+0.52 R⊕) is confirmed with >99.998% confidence using a combination of the planet multiplicity argument, an FP probability analysis, and a transit duration analysis.

Critical Slowing Down Governs the Transition to Neuron Spiking

PubMed Central

Meisel, Christian; Klaus, Andreas; Kuehn, Christian; Plenz, Dietmar

2015-01-01

Many complex systems have been found to exhibit critical transitions, or so-called tipping points, which are sudden changes to a qualitatively different system state. These changes can profoundly impact the functioning of a system ranging from controlled state switching to a catastrophic break-down; signals that predict critical transitions are therefore highly desirable. To this end, research efforts have focused on utilizing qualitative changes in markers related to a system’s tendency to recover more slowly from a perturbation the closer it gets to the transition—a phenomenon called critical slowing down. The recently studied scaling of critical slowing down offers a refined path to understand critical transitions: to identify the transition mechanism and improve transition prediction using scaling laws. Here, we outline and apply this strategy for the first time in a real-world system by studying the transition to spiking in neurons of the mammalian cortex. The dynamical system approach has identified two robust mechanisms for the transition from subthreshold activity to spiking, saddle-node and Hopf bifurcation. Although theory provides precise predictions on signatures of critical slowing down near the bifurcation to spiking, quantitative experimental evidence has been lacking. Using whole-cell patch-clamp recordings from pyramidal neurons and fast-spiking interneurons, we show that 1) the transition to spiking dynamically corresponds to a critical transition exhibiting slowing down, 2) the scaling laws suggest a saddle-node bifurcation governing slowing down, and 3) these precise scaling laws can be used to predict the bifurcation point from a limited window of observation. To our knowledge this is the first report of scaling laws of critical slowing down in an experiment. They present a missing link for a broad class of neuroscience modeling and suggest improved estimation of tipping points by incorporating scaling laws of critical slowing down as a strategy applicable to other complex systems. PMID:25706912

Metastable liquid-liquid transition in a molecular model of water

NASA Astrophysics Data System (ADS)

Palmer, Jeremy C.; Martelli, Fausto; Liu, Yang; Car, Roberto; Panagiotopoulos, Athanassios Z.; Debenedetti, Pablo G.

2014-06-01

Liquid water's isothermal compressibility and isobaric heat capacity, and the magnitude of its thermal expansion coefficient, increase sharply on cooling below the equilibrium freezing point. Many experimental, theoretical and computational studies have sought to understand the molecular origin and implications of this anomalous behaviour. Of the different theoretical scenarios put forward, one posits the existence of a first-order phase transition that involves two forms of liquid water and terminates at a critical point located at deeply supercooled conditions. Some experimental evidence is consistent with this hypothesis, but no definitive proof of a liquid-liquid transition in water has been obtained to date: rapid ice crystallization has so far prevented decisive measurements on deeply supercooled water, although this challenge has been overcome recently. Computer simulations are therefore crucial for exploring water's structure and behaviour in this regime, and have shown that some water models exhibit liquid-liquid transitions and others do not. However, recent work has argued that the liquid-liquid transition has been mistakenly interpreted, and is in fact a liquid-crystal transition in all atomistic models of water. Here we show, by studying the liquid-liquid transition in the ST2 model of water with the use of six advanced sampling methods to compute the free-energy surface, that two metastable liquid phases and a stable crystal phase exist at the same deeply supercooled thermodynamic condition, and that the transition between the two liquids satisfies the thermodynamic criteria of a first-order transition. We follow the rearrangement of water's coordination shell and topological ring structure along a thermodynamically reversible path from the low-density liquid to cubic ice. We also show that the system fluctuates freely between the two liquid phases rather than crystallizing. These findings provide unambiguous evidence for a liquid-liquid transition in the ST2 model of water, and point to the separation of time scales between crystallization and relaxation as being crucial for enabling it.

Metastable liquid-liquid transition in a molecular model of water.

PubMed

Palmer, Jeremy C; Martelli, Fausto; Liu, Yang; Car, Roberto; Panagiotopoulos, Athanassios Z; Debenedetti, Pablo G

2014-06-19

Liquid water's isothermal compressibility and isobaric heat capacity, and the magnitude of its thermal expansion coefficient, increase sharply on cooling below the equilibrium freezing point. Many experimental, theoretical and computational studies have sought to understand the molecular origin and implications of this anomalous behaviour. Of the different theoretical scenarios put forward, one posits the existence of a first-order phase transition that involves two forms of liquid water and terminates at a critical point located at deeply supercooled conditions. Some experimental evidence is consistent with this hypothesis, but no definitive proof of a liquid-liquid transition in water has been obtained to date: rapid ice crystallization has so far prevented decisive measurements on deeply supercooled water, although this challenge has been overcome recently. Computer simulations are therefore crucial for exploring water's structure and behaviour in this regime, and have shown that some water models exhibit liquid-liquid transitions and others do not. However, recent work has argued that the liquid-liquid transition has been mistakenly interpreted, and is in fact a liquid-crystal transition in all atomistic models of water. Here we show, by studying the liquid-liquid transition in the ST2 model of water with the use of six advanced sampling methods to compute the free-energy surface, that two metastable liquid phases and a stable crystal phase exist at the same deeply supercooled thermodynamic condition, and that the transition between the two liquids satisfies the thermodynamic criteria of a first-order transition. We follow the rearrangement of water's coordination shell and topological ring structure along a thermodynamically reversible path from the low-density liquid to cubic ice. We also show that the system fluctuates freely between the two liquid phases rather than crystallizing. These findings provide unambiguous evidence for a liquid-liquid transition in the ST2 model of water, and point to the separation of time scales between crystallization and relaxation as being crucial for enabling it.

Multiply Degenerate Exceptional Points and Quantum Phase Transitions

NASA Astrophysics Data System (ADS)

Borisov, Denis I.; Ružička, František; Znojil, Miloslav

2015-12-01

The realization of a genuine phase transition in quantum mechanics requires that at least one of the Kato's exceptional-point parameters becomes real. A new family of finite-dimensional and time-parametrized quantum-lattice models with such a property is proposed and studied. All of them exhibit, at a real exceptional-point time t = 0, the Jordan-block spectral degeneracy structure of some of their observables sampled by Hamiltonian H( t) and site-position Q( t). The passes through the critical instant t = 0 are interpreted as schematic simulations of non-equivalent versions of the Big-Bang-like quantum catastrophes.

Triple points and phase diagrams in the extended phase space of charged Gauss-Bonnet black holes in AdS space

NASA Astrophysics Data System (ADS)

Wei, Shao-Wen; Liu, Yu-Xiao

2014-08-01

We study the triple points and phase diagrams in the extended phase space of the charged Gauss-Bonnet black holes in d-dimensional anti-de Sitter space, where the cosmological constant appears as a dynamical pressure of the system and its conjugate quantity is the thermodynamic volume of the black holes. Employing the equation of state T=T(v,P), we demonstrate that the information of the phase transition and behavior of the Gibbs free energy are potential encoded in the T-v (T-rh) line with fixed pressure P. We get the phase diagrams for the charged Gauss-Bonnet black holes with different values of the charge Q and dimension d. The result shows that the small/large black hole phase transitions appear for any d, which is reminiscent of the liquid/gas transition of a Van der Waals type. Moreover, the interesting thermodynamic phenomena, i.e., the triple points and the small/intermediate/large black hole phase transitions are observed for d=6 and Q ∈(0.1705,0.1946).

Effect of correlations on controllability transition in network control

PubMed Central

Nie, Sen; Wang, Xu-Wen; Wang, Bing-Hong; Jiang, Luo-Luo

2016-01-01

The network control problem has recently attracted an increasing amount of attention, owing to concerns including the avoidance of cascading failures of power-grids and the management of ecological networks. It has been proven that numerical control can be achieved if the number of control inputs exceeds a certain transition point. In the present study, we investigate the effect of degree correlation on the numerical controllability in networks whose topological structures are reconstructed from both real and modeling systems, and we find that the transition point of the number of control inputs depends strongly on the degree correlation in both undirected and directed networks with moderately sparse links. More interestingly, the effect of the degree correlation on the transition point cannot be observed in dense networks for numerical controllability, which contrasts with the corresponding result for structural controllability. In particular, for directed random networks and scale-free networks, the influence of the degree correlation is determined by the types of correlations. Our approach provides an understanding of control problems in complex sparse networks. PMID:27063294

An intermittency route to global instability in low-density jets

NASA Astrophysics Data System (ADS)

Murugesan, Meenatchidevi; Zhu, Yuanhang; Li, Larry K. B.

2017-11-01

Above a critical Reynolds number (Re), a low-density jet can become globally unstable, transitioning from a steady state (i.e. a fixed point) to a self-excited oscillatory state (i.e. a limit cycle) via a Hopf bifurcation. In this experimental study, we show that this transition can sometimes involve intermittency. When Re is just slightly above the critical point, intermittent bursts of high-amplitude periodic oscillations emerge amidst a background of low-amplitude aperiodic fluctuations. As Re increases further, these intermittent bursts persist longer in time until they dominate the overall dynamics, causing the jet to transition fully to a periodic limit cycle. We identify this as Type-II Pomeau-Manneville intermittency by quantifying the statistical distribution of the duration of the aperiodic fluctuations at the onset of intermittency. This study shows that the transition to global instability in low-density jets is not always abrupt but can involve an intermediate state with characteristics of both the initial fixed point and the final limit cycle. This work was supported by the Research Grants Council of Hong Kong (Project No. 16235716 and 26202815).

Behavior of supercooled aqueous solutions stemming from hidden liquid-liquid transition in water.

PubMed

Biddle, John W; Holten, Vincent; Anisimov, Mikhail A

2014-08-21

A popular hypothesis that explains the anomalies of supercooled water is the existence of a metastable liquid-liquid transition hidden below the line of homogeneous nucleation. If this transition exists and if it is terminated by a critical point, the addition of a solute should generate a line of liquid-liquid critical points emanating from the critical point of pure metastable water. We have analyzed thermodynamic consequences of this scenario. In particular, we consider the behavior of two systems, H2O-NaCl and H2O-glycerol. We find the behavior of the heat capacity in supercooled aqueous solutions of NaCl, as reported by Archer and Carter [J. Phys. Chem. B 104, 8563 (2000)], to be consistent with the presence of the metastable liquid-liquid transition. We elucidate the non-conserved nature of the order parameter (extent of "reaction" between two alternative structures of water) and the consequences of its coupling with conserved properties (density and concentration). We also show how the shape of the critical line in a solution controls the difference in concentration of the coexisting liquid phases.

Views of Young People With Chronic Conditions on Transition From Pediatric to Adult Health Services

PubMed Central

Hislop, Jenni; Mason, Helen; Parr, Jeremy R.; Vale, Luke; Colver, Allan

2017-01-01

Purpose This study sought to identify and describe the views of young people with chronic conditions about the transition from pediatric to adult services. Methods Q methodology was used to identify young people’s views on transition. A set of 39 statements about transition was developed from an existing literature review and refined in consultation with local groups of young people. Statements were printed onto cards and a purposive sample of 44 young people with chronic health conditions was recruited, 41 remaining in the study. The young people were asked to sort the statement cards onto a Q-sort grid, according to their opinions from “strongly disagree” to “strongly agree.” Factor analysis was used to identify shared points of view (patterns of similarity between individual’s Q-sorts). Results Four distinct views on transition were identified from young people: (1) “a laid-back view of transition;” (2) “anxiety about transition;” (3) “wanting independence and autonomy during transition;” and (4) “valuing social interaction with family, peers, and professionals to assist transition.” Conclusions Successful transition is likely to be influenced by how young people view the process. Discussing and understanding young people’s views and preferences about transition should help clinicians and young people develop personalized planning for transition as a whole, and more specifically the point of transfer, leading to effective and efficient engagement with adult care. PMID:27287962

Views of Young People With Chronic Conditions on Transition From Pediatric to Adult Health Services.

PubMed

Hislop, Jenni; Mason, Helen; Parr, Jeremy R; Vale, Luke; Colver, Allan

2016-09-01

This study sought to identify and describe the views of young people with chronic conditions about the transition from pediatric to adult services. Q methodology was used to identify young people's views on transition. A set of 39 statements about transition was developed from an existing literature review and refined in consultation with local groups of young people. Statements were printed onto cards and a purposive sample of 44 young people with chronic health conditions was recruited, 41 remaining in the study. The young people were asked to sort the statement cards onto a Q-sort grid, according to their opinions from "strongly disagree" to "strongly agree." Factor analysis was used to identify shared points of view (patterns of similarity between individual's Q-sorts). Four distinct views on transition were identified from young people: (1) "a laid-back view of transition;" (2) "anxiety about transition;" (3) "wanting independence and autonomy during transition;" and (4) "valuing social interaction with family, peers, and professionals to assist transition." Successful transition is likely to be influenced by how young people view the process. Discussing and understanding young people's views and preferences about transition should help clinicians and young people develop personalized planning for transition as a whole, and more specifically the point of transfer, leading to effective and efficient engagement with adult care. Copyright © 2016 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.

General phase transition models for vehicular traffic with point constraints on the flow

NASA Astrophysics Data System (ADS)

Dal Santo, E.; Rosini, M. D.; Dymski, N.; Benyahia, M.

2017-12-01

We generalize the phase transition model studied in [R. Colombo. Hyperbolic phase transition in traffic flow.\\ SIAM J.\\ Appl.\\ Math., 63(2):708-721, 2002], that describes the evolution of vehicular traffic along a one-lane road. Two different phases are taken into account, according to whether the traffic is low or heavy. The model is given by a scalar conservation law in the \\emph{free-flow} phase and by a system of two conservation laws in the \\emph{congested} phase. In particular, we study the resulting Riemann problems in the case a local point constraint on the flux of the solutions is enforced.

s± pairing near a Lifshitz transition

DOE PAGES

Mishra, Vivek; Scalapino, Douglas J.; Maier, Thomas A.

2016-08-26

Observations of robust superconductivity in some of the iron based superconductors in the vicinity of a Lifshitz point where a spin density wave instability is suppressed as the hole band drops below the Fermi energy raise questions for spin-fluctuation theories. In this paper we discuss spin-fluctuation pairing for a bilayer Hubbard model, which goes through such a Lifshitz transition. Our results show s± pairing with a transition temperature that peaks beyond the Lifshitz point and a gap function that has essentially the same magnitude but opposite sign on the incipient hole band as it does on the electron band thatmore » has a Fermi surface.« less

A Search for Lost Planets in the Kepler Multi-Planet Systems and the Discovery of the Long-Period, Neptune-Sized Exoplanet Kepler-150 f

NASA Technical Reports Server (NTRS)

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2017-01-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a Swiss cheese-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or lost). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this Swiss cheesing may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at approximately 3.3% lost in the period range of P = 400 - 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipelines choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f (P = 637.2 days, RP = 3.86 R earth) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument.

A SEARCH FOR LOST PLANETS IN THE KEPLER MULTI-PLANET SYSTEMS AND THE DISCOVERY OF A LONG PERIOD, NEPTUNE-SIZED EXOPLANET KEPLER-150 F.

PubMed

Schmitt, Joseph R; Jenkins, Jon M; Fischer, Debra A

2017-04-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a "Swiss cheese"-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or "lost"). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this "Swiss cheesing" may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at ~3.3% lost in the period range of P = 400 - 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline's choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f ( P = 637.2 days, R P = 3.86 R ⊕ ) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument.

A SEARCH FOR LOST PLANETS IN THE KEPLER MULTI-PLANET SYSTEMS AND THE DISCOVERY OF A LONG PERIOD, NEPTUNE-SIZED EXOPLANET KEPLER-150 F

PubMed Central

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2018-01-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a “Swiss cheese”-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or “lost”). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this “Swiss cheesing” may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at ~3.3% lost in the period range of P = 400 – 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline’s choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f (P = 637.2 days, RP = 3.86 R⊕) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument. PMID:29375142

Molecular Simulation of the Free Energy for the Accurate Determination of Phase Transition Properties of Molecular Solids

NASA Astrophysics Data System (ADS)

Sellers, Michael; Lisal, Martin; Brennan, John

2015-06-01

Investigating the ability of a molecular model to accurately represent a real material is crucial to model development and use. When the model simulates materials in extreme conditions, one such property worth evaluating is the phase transition point. However, phase transitions are often overlooked or approximated because of difficulty or inaccuracy when simulating them. Techniques such as super-heating or super-squeezing a material to induce a phase change suffer from inherent timescale limitations leading to ``over-driving,'' and dual-phase simulations require many long-time runs to seek out what frequently results in an inexact location of phase-coexistence. We present a compilation of methods for the determination of solid-solid and solid-liquid phase transition points through the accurate calculation of the chemical potential. The methods are applied to the Smith-Bharadwaj atomistic potential's representation of cyclotrimethylene trinitramine (RDX) to accurately determine its melting point (Tm) and the alpha to gamma solid phase transition pressure. We also determine Tm for a coarse-grain model of RDX, and compare its value to experiment and atomistic counterpart. All methods are employed via the LAMMPS simulator, resulting in 60-70 simulations that total 30-50 ns. Approved for public release. Distribution is unlimited.

Detailed study of the water trimer potential energy surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fowler, J.E.; Schaefer, H.F. III

The potential energy surface of the water trimer has been studied through the use of ab initio quantum mechanical methods. Five stationary points were located, including one minimum and two transition states. All geometries were optimized at levels up to the double-[Zeta] plus polarization plus diffuse (DZP + diff) single and double excitation coupled cluster (CCSD) level of theory. CCSD single energy points were obtained for the minimum, two transition states, and the water monomer using the triple-[Zeta] plus double polarization plus diffuse (TZ2P + diff) basis at the geometries predicted by the DZP + diff CCSD method. Reported aremore » the following: geometrical parameters, total and relative energies, harmonic vibrational frequencies and infrared intensities for the minimum, and zero point vibrational energies for the minimum, two transition states, and three separated water molecules. 27 refs., 5 figs., 10 tabs.« less

Transitions between refrigeration regions in extremely short quantum cycles

NASA Astrophysics Data System (ADS)

Feldmann, Tova; Kosloff, Ronnie

2016-05-01

The relation between the geometry of refrigeration cycles and their performance is explored. The model studied is based on a coupled spin system. Small cycle times, termed sudden refrigerators, develop coherence and inner friction. We explore the interplay between coherence and energy of the working medium employing a family of sudden cycles with decreasing cycle times. At the point of maximum coherence the cycle changes geometry. This region of cycle times is characterized by a dissipative resonance where heat is dissipated both to the hot and cold baths. We rationalize the change of geometry of the cycle as a result of a half-integer quantization which maximizes coherence. From this point on, increasing or decreasing the cycle time, eventually leads to refrigeration cycles. The transition point between refrigerators and short circuit cycles is characterized by a transition from finite to singular dynamical temperature. Extremely short cycle times reach a universal limit where all cycles types are equivalent.

Contrarian behavior in a complex adaptive system

NASA Astrophysics Data System (ADS)

Liang, Y.; An, K. N.; Yang, G.; Huang, J. P.

2013-01-01

Contrarian behavior is a kind of self-organization in complex adaptive systems (CASs). Here we report the existence of a transition point in a model resource-allocation CAS with contrarian behavior by using human experiments, computer simulations, and theoretical analysis. The resource ratio and system predictability serve as the tuning parameter and order parameter, respectively. The transition point helps to reveal the positive or negative role of contrarian behavior. This finding is in contrast to the common belief that contrarian behavior always has a positive role in resource allocation, say, stabilizing resource allocation by shrinking the redundancy or the lack of resources. It is further shown that resource allocation can be optimized at the transition point by adding an appropriate size of contrarians. This work is also expected to be of value to some other fields ranging from management and social science to ecology and evolution.

Transition from regular to irregular reflection of cylindrical converging shock waves over convex obstacles

NASA Astrophysics Data System (ADS)

Vignati, F.; Guardone, A.

2017-11-01

An analytical model for the evolution of regular reflections of cylindrical converging shock waves over circular-arc obstacles is proposed. The model based on the new (local) parameter, the perceived wedge angle, which substitutes the (global) wedge angle of planar surfaces and accounts for the time-dependent curvature of both the shock and the obstacle at the reflection point, is introduced. The new model compares fairly well with numerical results. Results from numerical simulations of the regular to Mach transition—eventually occurring further downstream along the obstacle—point to the perceived wedge angle as the most significant parameter to identify regular to Mach transitions. Indeed, at the transition point, the value of the perceived wedge angle is between 39° and 42° for all investigated configurations, whereas, e.g., the absolute local wedge angle varies in between 10° and 45° in the same conditions.

Dielectric determination of the glass transition temperature (T sub g)

NASA Technical Reports Server (NTRS)

Ries, Heidi R.

1990-01-01

The objective is to determine the glass transition temperature of a polymer using a dielectric dissipation technique. A peak in the dissipation factor versus temperature curve is expected near the glass transition temperature T sub g. It should be noted that the glass transition is gradual rather than abrupt, so that the glass transition temperature T sub g is not clearly identifiable. In this case, the glass transition temperature is defined to be the temperature at the intersection point of the tangent lines to the dissipation factor versus temperature curve above and below the transition region, as illustrated.

Cell population structure prior to bifurcation predicts efficiency of directed differentiation in human induced pluripotent cells.

PubMed

Bargaje, Rhishikesh; Trachana, Kalliopi; Shelton, Martin N; McGinnis, Christopher S; Zhou, Joseph X; Chadick, Cora; Cook, Savannah; Cavanaugh, Christopher; Huang, Sui; Hood, Leroy

2017-02-28

Steering the differentiation of induced pluripotent stem cells (iPSCs) toward specific cell types is crucial for patient-specific disease modeling and drug testing. This effort requires the capacity to predict and control when and how multipotent progenitor cells commit to the desired cell fate. Cell fate commitment represents a critical state transition or "tipping point" at which complex systems undergo a sudden qualitative shift. To characterize such transitions during iPSC to cardiomyocyte differentiation, we analyzed the gene expression patterns of 96 developmental genes at single-cell resolution. We identified a bifurcation event early in the trajectory when a primitive streak-like cell population segregated into the mesodermal and endodermal lineages. Before this branching point, we could detect the signature of an imminent critical transition: increase in cell heterogeneity and coordination of gene expression. Correlation analysis of gene expression profiles at the tipping point indicates transcription factors that drive the state transition toward each alternative cell fate and their relationships with specific phenotypic readouts. The latter helps us to facilitate small molecule screening for differentiation efficiency. To this end, we set up an analysis of cell population structure at the tipping point after systematic variation of the protocol to bias the differentiation toward mesodermal or endodermal cell lineage. We were able to predict the proportion of cardiomyocytes many days before cells manifest the differentiated phenotype. The analysis of cell populations undergoing a critical state transition thus affords a tool to forecast cell fate outcomes and can be used to optimize differentiation protocols to obtain desired cell populations.

Transitional Instability, Psychological Health, and Sexual Risk Taking among College Students

ERIC Educational Resources Information Center

Bowers, Jill R.; Segrin, Chris

2017-01-01

This study examined the effects of transitional instability on college students' (n = 402) psychological distress and sexual risk taking at two different time points over one year. Tested through structural equation models, the data revealed transitional instability had significant positive effects on psychological distress and sexual risk taking…

The Juvenile Transition: A Developmental Switch Point in Human Life History

ERIC Educational Resources Information Center

Del Giudice, Marco; Angeleri, Romina; Manera, Valeria

2009-01-01

This paper presents a new perspective on the transition from early to middle childhood (i.e., human juvenility), investigated in an integrative evolutionary framework. Juvenility is a crucial life history stage, when social learning and interaction with peers become central developmental functions; here it is argued that the "juvenile transition"…

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β -Ga2O3

NASA Astrophysics Data System (ADS)

Mock, Alyssa; Korlacki, Rafał; Briley, Chad; Darakchieva, Vanya; Monemar, Bo; Kumagai, Yoshinao; Goto, Ken; Higashiwaki, Masataka; Schubert, Mathias

2017-12-01

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β -Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

Theory of quantum metal to superconductor transitions in highly conducting systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spivak, B.

2010-04-06

We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure whichmore » is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.« less

Phase transitions in semisupervised clustering of sparse networks

NASA Astrophysics Data System (ADS)

Zhang, Pan; Moore, Cristopher; Zdeborová, Lenka

2014-11-01

Predicting labels of nodes in a network, such as community memberships or demographic variables, is an important problem with applications in social and biological networks. A recently discovered phase transition puts fundamental limits on the accuracy of these predictions if we have access only to the network topology. However, if we know the correct labels of some fraction α of the nodes, we can do better. We study the phase diagram of this semisupervised learning problem for networks generated by the stochastic block model. We use the cavity method and the associated belief propagation algorithm to study what accuracy can be achieved as a function of α . For k =2 groups, we find that the detectability transition disappears for any α >0 , in agreement with previous work. For larger k where a hard but detectable regime exists, we find that the easy/hard transition (the point at which efficient algorithms can do better than chance) becomes a line of transitions where the accuracy jumps discontinuously at a critical value of α . This line ends in a critical point with a second-order transition, beyond which the accuracy is a continuous function of α . We demonstrate qualitatively similar transitions in two real-world networks.

Shock loading and release behavior of silicon nitride

NASA Astrophysics Data System (ADS)

Kawai, Nobuaki; Tsuru, Taiki; Hidaka, Naoto; Liu, Xun; Mashimo, Tsutomu

2015-06-01

Shock-reshock and shock-release experiments were performed on silicon nitride ceramics above and below its phase transition pressure. Experimental results clearly show the occurrence of elastic-plastic transition and phase transition during initial shock loading. The HEL and phase transition stress are determined as 11.6 GPa and 34.5 GPa, respectively. Below the phase transition point, the reshock profile consists of the single shock with short rise time, while the release profile shows the gradual release followed by more rapid one. Above the phase transition point, reshock and release behavior varies with the initial shock stress. In the case of reshock and release from about 40 GPa, the reshock structure is considerably dispersed, while the release structure shows rapid release. In the reshock profile from about 50 GPa, the formation of the shock wave with the small ramped precursor is observed. And, the release response from same condition shows initial gradual release and subsequent quite rapid one. These results would provide the information about how phase transformation kinetics effects on the reshock and release behavior.

Thermodynamic behavior of a phase transition in a model for sympatric speciation

NASA Astrophysics Data System (ADS)

Luz-Burgoa, K.; Moss de Oliveira, S.; Schwämmle, Veit; Sá Martins, J. S.

2006-08-01

We investigate the macroscopic effects of the ingredients that drive the origin of species through sympatric speciation. In our model, sympatric speciation is obtained as we tune up the strength of competition between individuals with different phenotypes. As a function of this control parameter, we can characterize, through the behavior of a macroscopic order parameter, a phase transition from a nonspeciation to a speciation state of the system. The behavior of the first derivative of the order parameter with respect to the control parameter is consistent with a phase transition and exhibits a sharp peak at the transition point. For different resources distribution, the transition point is shifted, an effect similar to pressure in a PVT system. The inverse of the parameter related to a sexual selection strength behaves like an external field in the system and, as thus, is also a control parameter. The macroscopic effects of the biological parameters used in our model are a reminiscent of the behavior of thermodynamic quantities in a phase transition of an equilibrium physical system.

Invalidity of the Fermi liquid theory and magnetic phase transition in quasi-1D dopant-induced armchair-edged graphene nanoribbons

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Davoudiniya, Masoumeh; Yarmohammadi, Mohsen

2018-04-01

Based on theoretically tight-binding calculations considering nearest neighbors and Green's function technique, we show that the magnetic phase transition in both semiconducting and metallic armchair graphene nanoribbons with width ranging from 9.83 Å to 69.3 Å would be observed in the presence of injecting electrons by doping. This transition is explained by the temperature-dependent static charge susceptibility through calculation of the correlation function of charge density operators. This work showed that charge concentration of dopants in such system plays a crucial role in determining the magnetic phase. A variety of multicritical points such as transition temperatures and maximum susceptibility are compared in undoped and doped cases. Our findings show that there exist two different transition temperatures and maximum susceptibility depending on the ribbon width in doped structures. Another remarkable point refers to the invalidity (validity) of the Fermi liquid theory in nanoribbons-based systems at weak (strong) concentration of dopants. The obtained interesting results of magnetic phase transition in such system create a new potential for magnetic graphene nanoribbon-based devices.

Synchrotron radiation topography studies of the phase transition in LaGaO 3 crystals

NASA Astrophysics Data System (ADS)

Yao, G.-D.; Dudley, M.; Wang, Y.; Liu, X.; Liebermann, R. C.

1991-05-01

An investigation of the orthorhombic to rhombohedral phase transformation occurring at 145°C in lanthanum gallate has been conducted using white beam synchrotron X-ray topography (WBSXRT). The existence of the first order transition was confirmed by differential thermal analysis and X-ray diffractometer powder analysis. Subsequent to this, synchrotron white beam Laue patterns were recorded in situ as a function of temperature, during the transition. Before the transition point was reached, (112) orth type reflection twinning was found to be dominant although a small amount of (110) orth type twinning was also observed in the same crystal. Beyond the transition point, not only did the structural change become evident but also reflection twinning on the (110) rhom planes was observed. The scale of this twinning became finer as the temperature was increased beyond the transition temperature. The twinning observed in both the low and high temperature phases gives rise to deformation of the (011) rhom surface plane which creates problems for the potential use of this material as a substrate for growing high Tc superconducting epitaxial layers.

Critical phenomena at the complex tensor ordering phase transition

NASA Astrophysics Data System (ADS)

Boettcher, Igor; Herbut, Igor F.

2018-02-01

We investigate the critical properties of the phase transition towards complex tensor order that has been proposed to occur in spin-orbit-coupled superconductors. For this purpose, we formulate the bosonic field theory for fluctuations of the complex irreducible second-rank tensor order parameter close to the transition. We then determine the scale dependence of the couplings of the theory by means of the perturbative renormalization group (RG). For the isotropic system, we generically detect a fluctuation-induced first-order phase transition. The initial values for the running couplings are determined by the underlying microscopic model for the tensorial order. As an example, we study three-dimensional Luttinger semimetals with electrons at a quadratic band-touching point. Whereas the strong-coupling transition of the model receives substantial fluctuation corrections, the weak-coupling transition at low temperatures is rendered only weakly first order due to the presence of a fixed point in the vicinity of the RG trajectory. If the number of fluctuating complex components of the order parameter is reduced by cubic anisotropy, the theory maps onto the field theory for frustrated magnetism.

Phase diagrams for sticky rods in bulk and in a monolayer from a lattice free-energy functional for anisotropic particles with depletion attractions

NASA Astrophysics Data System (ADS)

Mortazavifar, M.; Oettel, M.

2017-09-01

A density functional of fundamental measure type for a lattice model of anisotropic particles with hard-core repulsions and effective attractions is derived in the spirit of the Asakura-Oosawa model. Through polymeric lattice particles of various size and shape, effective attractions of different strength and range between the colloids can be generated. The functional is applied to the determination of phase diagrams for sticky rods of length L in two dimensions, in three dimensions, and in a monolayer system on a neutral substrate. In all cases, there is a competition between ordering and gas-liquid transitions. In two dimensions, this gives rise to a tricritical point, whereas in three dimensions, the isotropic-nematic transition crosses over smoothly to a gas-nematic liquid transition. The richest phase behavior is found for the monolayer system. For L =2 , two stable critical points are found corresponding to a standard gas-liquid transition and a nematic liquid-liquid transition. For L =3 , the gas-liquid transition becomes metastable.

Phase diagram for a two-dimensional, two-temperature, diffusive XY model.

PubMed

Reichl, Matthew D; Del Genio, Charo I; Bassler, Kevin E

2010-10-01

Using Monte Carlo simulations, we determine the phase diagram of a diffusive two-temperature conserved order parameter XY model. When the two temperatures are equal the system becomes the equilibrium XY model with the continuous Kosterlitz-Thouless (KT) vortex-antivortex unbinding phase transition. When the two temperatures are unequal the system is driven by an energy flow from the higher temperature heat-bath to the lower temperature one and reaches a far-from-equilibrium steady state. We show that the nonequilibrium phase diagram contains three phases: A homogenous disordered phase and two phases with long range, spin texture order. Two critical lines, representing continuous phase transitions from a homogenous disordered phase to two phases of long range order, meet at the equilibrium KT point. The shape of the nonequilibrium critical lines as they approach the KT point is described by a crossover exponent φ=2.52±0.05. Finally, we suggest that the transition between the two phases with long-range order is first-order, making the KT-point where all three phases meet a bicritical point.

Extremal black holes, Stueckelberg scalars and phase transitions

NASA Astrophysics Data System (ADS)

Marrani, Alessio; Miskovic, Olivera; Leon, Paula Quezada

2018-02-01

We calculate the entropy of a static extremal black hole in 4D gravity, non-linearly coupled to a massive Stueckelberg scalar. We find that the scalar field does not allow the black hole to be magnetically charged. We also show that the system can exhibit a phase transition due to electric charge variations. For spherical and hyperbolic horizons, the critical point exists only in presence of a cosmological constant, and if the scalar is massive and non-linearly coupled to electromagnetic field. On one side of the critical point, two extremal solutions coexist: Reissner-Nordström (A)dS black hole and the charged hairy (A)dS black hole, while on the other side of the critical point the black hole does not have hair. A near-critical analysis reveals that the hairy black hole has larger entropy, thus giving rise to a zero temperature phase transition. This is characterized by a discontinuous second derivative of the entropy with respect to the electric charge at the critical point. The results obtained here are analytical and based on the entropy function formalism and the second law of thermodynamics.

Weyl Semimetal to Metal Phase Transitions Driven by Quasiperiodic Potentials

NASA Astrophysics Data System (ADS)

Pixley, J. H.; Wilson, Justin H.; Huse, David A.; Gopalakrishnan, Sarang

2018-05-01

We explore the stability of three-dimensional Weyl and Dirac semimetals subject to quasiperiodic potentials. We present numerical evidence that the semimetal is stable for weak quasiperiodic potentials, despite being unstable for weak random potentials. As the quasiperiodic potential strength increases, the semimetal transitions to a metal, then to an "inverted" semimetal, and then finally to a metal again. The semimetal and metal are distinguished by the density of states at the Weyl point, as well as by level statistics, transport, and the momentum-space structure of eigenstates near the Weyl point. The critical properties of the transitions in quasiperiodic systems differ from those in random systems: we do not find a clear critical scaling regime in energy; instead, at the quasiperiodic transitions, the density of states appears to jump abruptly (and discontinuously to within our resolution).

Quantum phase transitions in the noncommutative Dirac oscillator

NASA Astrophysics Data System (ADS)

Panella, O.; Roy, P.

2014-10-01

We study the (2 + 1)-dimensional Dirac oscillator in a homogeneous magnetic field in the noncommutative plane. It is shown that the effect of noncommutativity is twofold: (i) momentum noncommuting coordinates simply shift the critical value (Bcr) of the magnetic field at which the well known left-right chiral quantum phase transition takes place (in the commuting phase); (ii) noncommutativity in the space coordinates induces a new critical value of the magnetic field, Bcr*, where there is a second quantum phase transition (right-left): this critical point disappears in the commutative limit. The change in chirality associated with the magnitude of the magnetic field is examined in detail for both critical points. The phase transitions are described in terms of the magnetization of the system. Possible applications to the physics of silicene and graphene are briefly discussed.

Phase diagram of the itinerant helical magnet MnSi at high pressures and strong magnetic fields

NASA Astrophysics Data System (ADS)

Stishov, Sergei

We performed a series of resistivity, heat capacity and ultrasound speed measurements of a MnSi single crystal at high pressures and strong magnetic fields [1-3]. Two notable features of the phase transition in MnSi that disappear on pressure increasin are a sharp peak marking the first order phase transition and a shallow maximum, situated slightly above the critical temperature and pointing to the domain of prominent helical fluctuations. The longitudinal and transverse ultrasound speeds and attenuation were measured in a MnSi single crystal in the temperature range of 2-40 K and magnetic fields to 7 Tesla. The magnetic phase transition in MnSi in zero magnetic field is signified by a quasi-discontinuity in the c11 elastic constant, which almost vanishes at the skyrmion - paramagnetic transition at high magnetic fields. The powerful fluctuations at the minima of c11 make the mentioned crossing point of the minima and the phase transition lines similar to a critical end point, where a second order phase transition meets a first order one.

The transition mechanisms of the E to H mode and the H to E mode in an inductively coupled argon-mercury mixture discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiao; Yu, Peng-Cheng; Liu, Yu

2015-10-15

In our experiment, the transition points between the two operational modes of capacitive coupling (E mode) and inductive coupling (H mode) were investigated at a wide range of mercury vapor pressures in an inductively coupled plasma, varying with the input radio-frequency powers and the total filling pressures (10 Pa–30 Pa). The electron temperatures were calculated versus with the mercury vapor pressures for different values of the total filling pressures. The transition power points and electron density also were measured in this study. It is shown that the transition powers, whether the E to H mode transition or the H to E modemore » transition, are lower than that of the argon discharge, and these powers almost increase with the mercury vapor pressure rising. However, the transition electron density follows an inverse relationship with the mercury vapor pressures compared with the transition powers. In addition, at the lower pressures and higher mercury vapor pressures, an inverse hysteresis was observed clearly, which did not appear in the argon gas plasma. We suggest that all these results are attributed to the electron-neutral collision frequency changed with the additional mercury vapor pressures.« less

Proof of Concept: Design and Initial Evaluation of a Device to Measure Gastrointestinal Transit Time.

PubMed

Wagner, Robert H; Savir-Baruch, Bital; Halama, James R; Venu, Mukund; Gabriel, Medhat S; Bova, Davide

2017-09-01

Chronic constipation and gastrointestinal motility disorders constitute a large part of a gastroenterology practice and have a significant impact on a patient's quality of life and lifestyle. In most cases, medications are prescribed to alleviate symptoms without there being an objective measurement of response. Commonly used investigations of gastrointestinal transit times are currently limited to radiopaque markers or electronic capsules. Repeated use of these techniques is limited because of the radiation exposure and the significant cost of the devices. We present the proof of concept for a new device to measure gastrointestinal transit time using commonly available and inexpensive materials with only a small amount of radiotracer. Methods: We assembled gelatin capsules containing a 67 Ga-citrate-radiolabeled grain of rice embedded in paraffin for use as a point-source transit device. It was tested for stability in vitro and subsequently was given orally to 4 healthy volunteers and 10 patients with constipation or diarrhea. Imaging was performed at regular intervals until the device was excreted. Results: The device remained intact and visible as a point source in all subjects until excretion. When used along with a diary of bowel movement times and dates, the device could determine the total transit time. The device could be visualized either alone or in combination with a barium small-bowel follow-through study or a gastric emptying study. Conclusion: The use of a point-source transit device for the determination of gastrointestinal transit time is a feasible alternative to other methods. The device is inexpensive and easy to assemble, requires only a small amount of radiotracer, and remains inert throughout the gastrointestinal tract, allowing for accurate determination of gastrointestinal transit time. Further investigation of the device is required to establish optimum imaging parameters and reference values. Measurements of gastrointestinal transit time may be useful in managing patients with dysmotility and in selecting the appropriate pharmaceutical treatment. © 2017 by the Society of Nuclear Medicine and Molecular Imaging.

Structural phases arising from reconstructive and isostructural transitions in high-melting-point oxides under hydrostatic pressure: A first-principles study

NASA Astrophysics Data System (ADS)

Tian, Hao; Kuang, Xiao-Yu; Mao, Ai-Jie; Yang, Yurong; Xu, Changsong; Sayedaghaee, S. Omid; Bellaiche, L.

2018-01-01

High-melting-point oxides of chemical formula A B O3 with A =Ca , Sr, Ba and B =Zr , Hf are investigated as a function of hydrostatic pressure up to 200 GPa by combining first-principles calculations with a particle swarm optimization method. Ca- and Sr-based systems: (1) first undergo a reconstructive phase transition from a perovskite state to a novel structure that belongs to the post-post-perovskite family and (2) then experience an isostructural transition to a second, also new post-post-perovskite state at higher pressures, via the sudden formation of a specific out-of-plane B -O bond. In contrast, the studied Ba compounds evolve from a perovskite phase to a third novel post-post-perovskite structure via another reconstructive phase transition. The original characteristics of these three different post-post-perovskite states are emphasized. Unusual electronic properties, including significant piezochromic effects and an insulator-metal transition, are also reported and explained.

Anomalies in the coil-stretch transition of flexible polymers

NASA Astrophysics Data System (ADS)

Ghosal, Aishani; Cherayil, Binny J.

2018-03-01

The flow-induced coil-stretch transition of high molecular weight polymers has generally been held to be of first order. But evidence of significant slowing down in the rate at which the polymers relax to equilibrium in the vicinity of the transition suggests that the thermodynamic character of the transition may be less clear-cut. The above slowing down effect is actually characteristic of a second-order transition, and it points to the existence of a broad spectrum of conformational states in the transition region, analogous to the existence of fluctuations of all length scales at a critical point. In this paper, using a path integral approach based on a free-draining finitely extensible chain model, we calculate various polymer properties as a function of elongational flow as a way of exploring different statistical mechanical details of the coil-stretch transition. These properties include the molecular weight dependence of the flow-extension curve of the polymer, the distribution of its steady-state end-to-end distances, and the characteristic relaxation time τR of these distances. Among other findings, our calculations indicate that the coil-stretch transition is discontinuous in the N → ∞ limit, that the effective free energy of the chain is unimodal at all values of the flow, becoming broad and flat in the immediate vicinity of the transition, and that the ratio of τR to the Rouse relaxation time increases abruptly at the transition before eventually reaching a plateau value at large flow strengths. These aspects of the coil-stretch transition place it among a larger class of unconventional nominally first-order single chain transitions that include the adsorption transition of surface-tethered polymers and the escape transition of compressed polymers.

Scaled-Up Nonequilibrium Air Plasmas

DTIC Science & Technology

2009-10-01

surrounding gas. So if we put a needle electrode with DC corona discharge directly into the MW plasma (Figure 7), N2* is produced by electron excitation but...transitions When a high voltage of a few kV is applied to the point electrode , a corona discharge appears on the point, further developing to streamer... electrode tips but with the smaller difference between the field in the middle and near the tips than in corona . This transition to TS pulse probably

Enhancing transit polio vaccination in collaboration with targeted stakeholders in Kaduna State, Nigeria: Lessons learnt: 2014-2015.

PubMed

Musa, Audu; Abba, Bashir; Ningi, Adamu M I; Gali, Emanuel; Bawa, Samuel; Manneh, Fadninding; Mkanda, Pascal; Banda, Richard; Yehuluashet, Yared G; Tegegne, Sisay G; Umeh, Gregory; Nsubuga, Peter; Etsano, Andrew; Shuaib, Faisal; Mohammed, Ado; Vaz, Rui G

2016-10-10

In Kaduna State of Nigeria, the high influx of people from neighboring states with eligible children for polio vaccination represents a significant proportion of the target population. Many of these children are often missed by the vaccination team. The purpose of the study was to determine the contribution of targeted stakeholders in transit polio vaccination. We used the trends of vaccinated children at transit points, motor parks and markets, well as total children vaccinated by transit teams in Chikun, Igabi and Sabon Gari Local Government Areas (LGAs) of Kaduna State, Nigeria, four rounds before and after the introduction of transit polio vaccination with targeted stakeholders in Kaduna State. A total of 87,502 under-5 children were vaccinated by the various transit teams in the three LGAs, which accounted for 3.2% of the total 2,781,162 children vaccinated by the three LGAs. For transit point vaccination, the number of vaccinated children increased from 1026 to 19,289 (302%), while motor park vaccination increased from 1289 to 4106 (318%) and market vaccination increased from 10,488 to 14,511 (138%), four rounds after the introduction of transit polio vaccination with targeted stakeholders. Engagement of targeted stakeholders significantly enhanced transit polio vaccination in Kaduna State, Nigeria. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Critical behavior of dissipative two-dimensional spin lattices

NASA Astrophysics Data System (ADS)

Rota, R.; Storme, F.; Bartolo, N.; Fazio, R.; Ciuti, C.

2017-04-01

We explore critical properties of two-dimensional lattices of spins interacting via an anisotropic Heisenberg Hamiltonian that are subject to incoherent spin flips. We determine the steady-state solution of the master equation for the density matrix via the corner-space renormalization method. We investigate the finite-size scaling and critical exponent of the magnetic linear susceptibility associated with a dissipative ferromagnetic transition. We show that the von Neumann entropy increases across the critical point, revealing a strongly mixed character of the ferromagnetic phase. Entanglement is witnessed by the quantum Fisher information, which exhibits a critical behavior at the transition point, showing that quantum correlations play a crucial role in the transition.

LaCu6-xAgx : A promising host of an elastic quantum critical point

NASA Astrophysics Data System (ADS)

Poudel, L.; Cruz, C. de la; Koehler, M. R.; McGuire, M. A.; Keppens, V.; Mandrus, D.; Christianson, A. D.

2018-05-01

Structural properties of LaCu6-xAgx have been investigated using neutron and x-ray diffraction, and resonant ultrasound spectroscopy (RUS) measurements. Diffraction measurements indicate a continuous structural transition from orthorhombic (Pnma) to monoclinic (P21 / c) structure. RUS measurements show softening of natural frequencies at the structural transition, consistent with the elastic nature of the structural ground state. The structural transition temperatures in LaCu6-xAgx decrease with Ag composition until the monoclinic phase is completely suppressed at xc = 0.225 . All of the evidence is consistent with the presence of an elastic quantum critical point in LaCu6-xAgx .

LaCu 6-xAg x: A promising host of an elastic quantum critical point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poudel, Lekh; Dela Cruz, Clarina R.; Koehler, Michael R.

Structural properties of LaCu 6-xAg x have been investigated using neutron and x-ray diffraction, and resonant ultrasound spectroscopy (RUS) measurements. Diffraction measurements indicate a continuous structural transition from orthorhombic (Pnma) to monoclinic (P2₁/C) structure. RUS measurements show softening of natural frequencies at the structural transition, consistent with the elastic nature of the structural ground state. The structural transition temperatures in LaCu 6-xAg x decrease with Ag composition until the monoclinic phase is completely suppressed at x c=0.225. All of the evidence is consistent with the presence of an elastic quantum critical point in LaCu 6-xAg x.

Information cascade on networks

NASA Astrophysics Data System (ADS)

Hisakado, Masato; Mori, Shintaro

2016-05-01

In this paper, we discuss a voting model by considering three different kinds of networks: a random graph, the Barabási-Albert (BA) model, and a fitness model. A voting model represents the way in which public perceptions are conveyed to voters. Our voting model is constructed by using two types of voters-herders and independents-and two candidates. Independents conduct voting based on their fundamental values; on the other hand, herders base their voting on the number of previous votes. Hence, herders vote for the majority candidates and obtain information relating to previous votes from their networks. We discuss the difference between the phases on which the networks depend. Two kinds of phase transitions, an information cascade transition and a super-normal transition, were identified. The first of these is a transition between a state in which most voters make the correct choices and a state in which most of them are wrong. The second is a transition of convergence speed. The information cascade transition prevails when herder effects are stronger than the super-normal transition. In the BA and fitness models, the critical point of the information cascade transition is the same as that of the random network model. However, the critical point of the super-normal transition disappears when these two models are used. In conclusion, the influence of networks is shown to only affect the convergence speed and not the information cascade transition. We are therefore able to conclude that the influence of hubs on voters' perceptions is limited.

Making a Drama out of Transition: Challenges and Opportunities at Times of Change

ERIC Educational Resources Information Center

Hammond, Nick

2016-01-01

This case study explored how teachers and children perceive challenges and opportunities at transition. Using Forum Theatre (FT), an interactive drama approach, children were able to show aspects of transitions they perceived as challenging and how these barriers may be overcome. FT offered a tangible reference point for children to discuss their…

The Trajectory of Popularity Goal during the Transition to Middle School

ERIC Educational Resources Information Center

Dawes, Molly; Xie, Hongling

2017-01-01

The trajectory of early adolescents' popularity goal during the transition to middle school was examined in a diverse sample of 401 students. Popularity goal was assessed at five time points from the spring semester of fifth grade through the spring semester of seventh grade with the transition to middle school occurring between the fifth and…

On the reversibility of the Meissner effect and the angular momentum puzzle

NASA Astrophysics Data System (ADS)

Hirsch, J. E.

2016-10-01

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay of eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes.

SU-F-T-17: A Feasibility Study for the Transit Dosimetry with a Glass Dosimeter in Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moon, S; Yoon, M; Chung, W

Purpose: Confirming the dose delivered to a patient is important to make sure the treatment quality and safety of the radiotherapy. Measuring a transit dose of the patient during the radiotherapy could be an interesting way to confirm the patient dose. In this study, we evaluated the feasibility of the transit dosimetry with a glass dosimeter in brachytherapy. Methods: We made a phantom that inserted the glass dosimeters and placed under patient lying on a couch for cervix cancer brachytherapy. The 18 glass dosimeters were placed in the phantom arranged 6 per row. A point putting 1cm vertically from themore » source was prescribed as 500.00 cGy. Solid phantoms of 0, 2, 4, 6, 8, 10 cm were placed between the source and the glass dosimeter. The transit dose was measured each thickness using the glass dosimeters and compared with a treatment planning system (TPS). Results: When the transit dose was smaller than 10 cGy, the average of the differences between measured values and calculated values by TPS was 0.50 cGy and the standard deviation was 0.69 cGy. If the transit dose was smaller than 100 cGy, the average of the error was 1.67 ± 4.01 cGy. The error to a point near the prescription point was −14.02 cGy per 500.00 cGy of the prescription dose. Conclusion: The distances from the sources to skin of the patient generally are within 10 cm for cervix cancer cases in brachytherapy. The results of this preliminary study showed the probability of the glass dosimeter as the transit dosimeter in brachytherapy.« less

Dissipation-Induced Anomalous Multicritical Phenomena

NASA Astrophysics Data System (ADS)

Soriente, M.; Donner, T.; Chitra, R.; Zilberberg, O.

2018-05-01

We explore the influence of dissipation on a paradigmatic driven-dissipative model where a collection of two level atoms interact with both quadratures of a quantum cavity mode. The closed system exhibits multiple phase transitions involving discrete and continuous symmetries breaking and all phases culminate in a multicritical point. In the open system, we show that infinitesimal dissipation erases the phase with broken continuous symmetry and radically alters the model's phase diagram. The multicritical point now becomes brittle and splits into two tricritical points where first- and second-order symmetry-breaking transitions meet. A quantum fluctuations analysis shows that, surprisingly, the tricritical points exhibit anomalous finite fluctuations, as opposed to standard tricritical points arising in He 3 -He 4 mixtures. Our work has direct implications for a variety of fields, including cold atoms and ions in optical cavities, circuit-quantum electrodynamics as well as optomechanical systems.

Predicting Transition from Laminar to Turbulent Flow over a Surface

NASA Technical Reports Server (NTRS)

Sturdza, Peter (Inventor); Rajnarayan, Dev (Inventor)

2013-01-01

A prediction of whether a point on a computer-generated surface is adjacent to laminar or turbulent flow is made using a transition prediction technique. A plurality of boundary-layer properties at the point are obtained from a steady-state solution of a fluid flow in a region adjacent to the point. A plurality of instability modes are obtained, each defined by one or more mode parameters. A vector of regressor weights is obtained for the known instability growth rates in a training dataset. For each instability mode in the plurality of instability modes, a covariance vector is determined, which is the covariance of a predicted local growth rate with the known instability growth rates. Each covariance vector is used with the vector of regressor weights to determine a predicted local growth rate at the point. Based on the predicted local growth rates, an n-factor envelope at the point is determined.

System-size convergence of point defect properties: The case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Corsetti, Fabiano; Mostofi, Arash A.

2011-07-01

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Γ-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Γ-point quickly converges to a fixed value which correctly describes the bonding at the defect center. Our calculated transition levels with 1000-atom supercells and Γ-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect center that verifies the canonical Watkins model.

Behavior of supercooled aqueous solutions stemming from hidden liquid–liquid transition in water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biddle, John W.; Holten, Vincent; Anisimov, Mikhail A., E-mail: anisimov@umd.edu

2014-08-21

A popular hypothesis that explains the anomalies of supercooled water is the existence of a metastable liquid–liquid transition hidden below the line of homogeneous nucleation. If this transition exists and if it is terminated by a critical point, the addition of a solute should generate a line of liquid–liquid critical points emanating from the critical point of pure metastable water. We have analyzed thermodynamic consequences of this scenario. In particular, we consider the behavior of two systems, H{sub 2}O-NaCl and H{sub 2}O-glycerol. We find the behavior of the heat capacity in supercooled aqueous solutions of NaCl, as reported by Archermore » and Carter [J. Phys. Chem. B 104, 8563 (2000)], to be consistent with the presence of the metastable liquid–liquid transition. We elucidate the non-conserved nature of the order parameter (extent of “reaction” between two alternative structures of water) and the consequences of its coupling with conserved properties (density and concentration). We also show how the shape of the critical line in a solution controls the difference in concentration of the coexisting liquid phases.« less

Method and apparatus for ultrasonic characterization through the thickness direction of a moving web

DOEpatents

Jackson, Theodore; Hall, Maclin S.

2001-01-01

A method and apparatus for determining the caliper and/or the ultrasonic transit time through the thickness direction of a moving web of material using ultrasonic pulses generated by a rotatable wheel ultrasound apparatus. The apparatus includes a first liquid-filled tire and either a second liquid-filled tire forming a nip or a rotatable cylinder that supports a thin moving web of material such as a moving web of paper and forms a nip with the first liquid-filled tire. The components of ultrasonic transit time through the tires and fluid held within the tires may be resolved and separately employed to determine the separate contributions of the two tire thicknesses and the two fluid paths to the total path length that lies between two ultrasonic transducer surfaces contained within the tires in support of caliper measurements. The present invention provides the benefit of obtaining a transit time and caliper measurement at any point in time as a specimen passes through the nip of rotating tires and eliminates inaccuracies arising from nonuniform tire circumferential thickness by accurately retaining point-to-point specimen transit time and caliper variation information, rather than an average obtained through one or more tire rotations. Morever, ultrasonic transit time through the thickness direction of a moving web may be determined independent of small variations in the wheel axle spacing, tire thickness, and liquid and tire temperatures.

Uniform phases in fluids of hard isosceles triangles: One-component fluid and binary mixtures

NASA Astrophysics Data System (ADS)

Martínez-Ratón, Yuri; Díaz-De Armas, Ariel; Velasco, Enrique

2018-05-01

We formulate the scaled particle theory for a general mixture of hard isosceles triangles and calculate different phase diagrams for the one-component fluid and for certain binary mixtures. The fluid of hard triangles exhibits a complex phase behavior: (i) the presence of a triatic phase with sixfold symmetry, (ii) the isotropic-uniaxial nematic transition is of first order for certain ranges of aspect ratios, and (iii) the one-component system exhibits nematic-nematic transitions ending in critical points. We found the triatic phase to be stable not only for equilateral triangles but also for triangles of similar aspect ratios. We focus the study of binary mixtures on the case of symmetric mixtures: equal particle areas with aspect ratios (κi) symmetric with respect to the equilateral one, κ1κ2=3 . For these mixtures we found, aside from first-order isotropic-nematic and nematic-nematic transitions (the latter ending in a critical point): (i) a region of triatic phase stability even for mixtures made of particles that do not form this phase at the one-component limit, and (ii) the presence of a Landau point at which two triatic-nematic first-order transitions and a nematic-nematic demixing transition coalesce. This phase behavior is analogous to that of a symmetric three-dimensional mixture of rods and plates.

Photometric Analysis and Transit Times of TRAPPIST-1 B and C

NASA Astrophysics Data System (ADS)

Morris, Brett M.; Agol, Eric; Hawley, Suzanne L.

2018-01-01

TRAPPIST-1 hosts seven Earth-sized planets transiting an M8 star. We observed mid-transit times of each of the inner two planets with the Astrophysical Research Consortium (ARC) 3.5 m Telescope at Apache Point Observatory (APO) to help constrain the planet masses with transit timing variations, and we outline a procedure for analyzing transit observations of late-M stars with APO. The transit times of TRAPPIST-1 b and c are $\\mathrm{BJD}_{\\mathrm{TDB}} = 2457580.87634^{+0.00034}_{-0.00034}$ and $2457558.89477^{+0.00080}_{-0.00085}$, respectively, which will help constrain the planet masses.

Market Based Transit Facility Design

DOT National Transportation Integrated Search

1989-02-01

The purpose of this report is to provide guidelines for the planning and design of transit stations, stops, and terminals. These guidelines have been prepared form a market-based point of view. Design elements are suggested that directly relate promo...

Design of Three-Dimensional Hypersonic Inlets with Rectangular to Elliptical Shape Transition

NASA Technical Reports Server (NTRS)

Smart, M. K.

1998-01-01

A methodology has been devised for the design of three-dimensional hypersonic inlets which include a rectangular to elliptical shape transition. This methodology makes extensive use of inviscid streamtracing techniques to generate a smooth shape transition from a rectangular-like capture to an elliptical throat. Highly swept leading edges and a significantly notched cowl enable use of these inlets in fixed geometry configurations. The design procedure includes a three dimensional displacement thickness calculation and uses established correlations to check for boundary layer separation due to shock wave interactions. Complete details of the design procedure are presented and the characteristics of a modular inlet with rectangular to elliptical shape transition and a design point of Mach 7.1 are examined. Comparison with a classical two-dimensional inlet optimized for maximum total pressure recovery indicates that this three-dimensional inlet demonstrates good performance even well below its design point.

What can nuclear collisions teach us about the boiling of water or the formation of multi-star systems

NASA Astrophysics Data System (ADS)

Gross, D. H. E.

2001-11-01

Phase transitions in nuclei, small atomic clusters and self-gravitating systems demand the extension of thermo-statistics to "Small" systems. The main obstacle is the thermodynamic limit. It is shown how the original definition of the entropy by Boltzmann as the volume of the energy-manifold of the N-body phase space allows a geometrical definition of the entropy as function of the conserved quantities. Without invoking the thermodynamic limit the whole "zoo" of phase transitions and critical points/lines can be unambiguously defined. The relation to the Yang-Lee singularities of the grand-canonical partition sum is pointed out. It is shown that just phase transitions in non-extensive systems give the complete set of characteristic parameters of the transition including the surface tension. Nuclear heavy-ion collisions are an experimental playground to explore this extension of thermo-statistics

From bosonic topological transition to symmetric fermion mass generation

NASA Astrophysics Data System (ADS)

You, Yi-Zhuang; He, Yin-Chen; Vishwanath, Ashvin; Xu, Cenke

2018-03-01

A bosonic topological transition (BTT) is a quantum critical point between the bosonic symmetry-protected topological phase and the trivial phase. In this work, we investigate such a transition in a (2+1)-dimensional lattice model with the maximal microscopic symmetry: an internal SO (4 ) symmetry. We derive a description for this transition in terms of compact quantum electrodynamics (QED) with four fermion flavors (Nf=4 ). Within a systematic renormalization group analysis, we identify the critical point with the desired O (4 ) emergent symmetry and all expected deformations. By lowering the microscopic symmetry, we recover the previous Nf=2 noncompact QED description of the BTT. Finally, by merging two BTTs we recover a previously discussed theory of symmetric mass generation, as an SU (2 ) quantum chromodynamics-Higgs theory with Nf=4 flavors of SU (2 ) fundamental fermions and one SU (2 ) fundamental Higgs boson. This provides a consistency check on both theories.

Community detection in networks with unequal groups.

PubMed

Zhang, Pan; Moore, Cristopher; Newman, M E J

2016-01-01

Recently, a phase transition has been discovered in the network community detection problem below which no algorithm can tell which nodes belong to which communities with success any better than a random guess. This result has, however, so far been limited to the case where the communities have the same size or the same average degree. Here we consider the case where the sizes or average degrees differ. This asymmetry allows us to assign nodes to communities with better-than-random success by examining their local neighborhoods. Using the cavity method, we show that this removes the detectability transition completely for networks with four groups or fewer, while for more than four groups the transition persists up to a critical amount of asymmetry but not beyond. The critical point in the latter case coincides with the point at which local information percolates, causing a global transition from a less-accurate solution to a more-accurate one.

Early-warning signals of critical transition: Effect of extrinsic noise

NASA Astrophysics Data System (ADS)

Qin, Shanshan; Tang, Chao

2018-03-01

Complex dynamical systems often have tipping points and exhibit catastrophic regime shift. Despite the notorious difficulty of predicting such transitions, accumulating studies have suggested the existence of generic early-warning signals (EWSs) preceding upcoming transitions. However, previous theories and models were based on the effect of the intrinsic noise (IN) when a system is approaching a critical point, and did not consider the pervasive environmental fluctuations or the extrinsic noise (EN). Here, we extend previous theory to investigate how the interplay of EN and IN affects EWSs. Stochastic simulations of model systems subject to both IN and EN have verified our theory and demonstrated that EN can dramatically alter and diminish the EWS. This effect is stronger with increasing amplitude and correlation time scale of the EN. In the presence of EN, the EWS can fail to predict or even give a false alarm of critical transitions.

Micellization and phase transitions in a triblock copolymer-D2O system

NASA Astrophysics Data System (ADS)

Odhner, Hosanna; Huff, Alison; Patton, Kelly; Jacobs, D. T.; Clover, Bryna; Greer, Sandra

2011-03-01

The triblock copolymer (``unimer'') of PPO-PEO-PPO (commercially known as 17R4) has hydrophobic ends and a hydrophilic center. When placed in D2 O at lower concentrations and temperatures, only a network of unimers exists. However, at higher concentrations or temperatures, micelles of different geometries can form. We have measured the micellization line marking the transition from only unimers to some micelles, as well as a one- to two-phase transition at higher temperatures. This second transition is an Ising-like, LCST critical point, based on the shape of the coexistence curve. We find the LCST to not correspond to the minimum of the cloud point curve, which indicates polydispersity as described by Sollich. We acknowledge the support from Research Corporation, NSF-REU grant DMR 0649112, The College of Wooster, and (for BC and SG) to the donors of the Petroleum Research Fund, administered by the American Chemical Society.

The Interplay Between Language, Gesture, and Affect During Communicative Transition: A Dynamic Systems Approach

PubMed Central

Parladé, Meaghan V.; Iverson, Jana M.

2012-01-01

From a dynamic systems perspective, transition points in development are times of increased instability, during which behavioral patterns are susceptible to temporary decoupling. This study investigated the impact of the vocabulary spurt on existing patterns of communicative coordination. Eighteen typically developing infants were videotaped at home 1 month before, at, and after the vocabulary spurt. Infants were identified as spurters if they underwent a discrete phase transition in vocabulary development (marked by an inflection point), and compared with a group of nonspurters whose word-learning rates followed a trajectory of continuous change. Relative to surrounding sessions, there were significant reductions in overall coordination of communicative behaviors and in words produced in coordination at the vocabulary spurt session for infants who experienced more dramatic vocabulary growth. In contrast, nonspurters demonstrated little change across sessions. Findings underscore the importance of transitions as opportunities for observing processes of developmental change. PMID:21219063

Metal-insulator transition and superconductivity induced by Rh doping in the binary pnictides RuPn (Pn=P, As, Sb)

NASA Astrophysics Data System (ADS)

Hirai, Daigorou; Takayama, Tomohiro; Hashizume, Daisuke; Takagi, Hidenori

2012-04-01

Binary ruthenium pnictides, RuP and RuAs, with an orthorhombic MnP structure, were found to show a metal to a nonmagnetic insulator transition at TMI = 270 and 200 K, respectively. In the metallic region above TMI, a structural phase transition, accompanied with a weak anomaly in the resistivity and the magnetic susceptibility, indicative of a pseudogap formation, was identified at Ts = 330 and 280 K, respectively. These two transitions were suppressed by substituting Ru with Rh. We found superconductivity with a maximum Tc = 3.7 and 1.8 K in a narrow composition range around the critical point for the pseudogap phase, Rh content xc = 0.45 and 0.25 for Ru1-xRhxP and Ru1-xRhxAs, respectively, which may provide us with a nonmagnetic route to superconductivity at a quantum critical point.

Raman Scattering Study of the Soft Phonon Mode in the Hexagonal Ferroelectric Crystal KNiCl 3

NASA Astrophysics Data System (ADS)

Machida, Ken-ichi; Kato, Tetsuya; Chao, Peng; Iio, Katsunori

1997-10-01

Raman spectra of some phonon modes of the hexagonal ferroelectriccrystal KNiCl3are obtained in the temperature range between 290 K and 590 K, which includes the structural phase transition point T2(=561 K) at which previous measurements of dielectric constant and spontaneouspolarization as a function of temperature had shown that KNiCl3 undergoes a transition between polar phases II and III. An optical birefringence measurement carried outas a complement to the present Raman scattering revealed that this transition is of second order. Towards this transition point, the totally symmetric phonon mode with the lowest frequency observed in the room-temperature phasewas found to soften with increasing temperature.The present results provide new information on the phase-transitionmechanism and the space groups of thehigher (II)- and lower (III)-symmetric phases around T2.

Unraveling energy conversion modeling in the intrinsic persistent upconverted luminescence of solids: a study of native point defects in antiferromagnetic Er2O3.

PubMed

Huang, Bolong

2016-05-11

We investigated the mechanism of the intrinsic persistent luminescence of Er2O3 in the A-type lattice based on first-principles calculations. We found that the native point defects were engaged in mutual subtle interactions in the form of chemical reactions between different charge states. The release of energy related to lattice distortion facilitates the conversion of energy for electrons to be transported between the valence band and the trap levels or even between the deep trap levels so as to generate persistent luminescence. The defect transitions that take place along the zero-phonon line release energy to enable optical transitions, with the exact amount of negative effective correlation energy determined by the lattice distortions. Our calculations on the thermodynamic transition levels confirm that both the visible and NIR experimentally observed intrinsic persistent luminescence (phosphor or afterglow) are related to the thermodynamic transition levels of oxygen-related defects, and the thermodynamic transition levels within different charge states for these defects are independent of the chemical potentials of the given species. Lattice distortion defects such as anion Frenkel (a-Fr) pair defects play an important role in transporting O-related defects between different lattice sites. To obtain red persistent luminescence that matches the biological therapeutic window, it is suggested to increase the electron transition levels between high-coordinated O vacancies and related metastable a-Fr defects; a close-packed core-shell structure is required to quench low-coordinated O-related defects so as to reduce the green band luminescence. We further established a conversed chain reaction (CCR) model to interpret the energy conversion process of persistent luminescence in terms of the inter-reactions of native point defects between different charge states. It is advantageous to use the study of defect levels combined with formation energies to suggest limits to doping energy and explain photostimulated luminescence in terms of native point defects.

Wetting Behavior in Colloid-Polymer Mixtures at Different Substrates.

PubMed

Wijting, Willem K; Besseling, Nicolaas A M; Cohen Stuart, Martien A

2003-09-25

We present experimental observations on wetting phenomena in depletion interaction driven, phase separated colloidal dispersions. The contact angle of the colloidal liquid-gas interface at a solid substrate was determined for a series of compositions. Upon approach to the critical point, a transition occurs from partial to complete wetting. The interaction with the substrate was manipulated by modifying the substrate with a polymer. In that case, a transition from partial to complete drying is observed upon approach to the critical point.

Dirac points, spinons and spin liquid in twisted bilayer graphene

NASA Astrophysics Data System (ADS)

Irkhin, V. Yu.; Skryabin, Yu. N.

2018-05-01

Twisted bilayer graphene is an excellent example of highly correlated system demonstrating a nearly flat electron band, the Mott transition and probably a spin liquid state. Besides the one-electron picture, analysis of Dirac points is performed in terms of spinon Fermi surface in the limit of strong correlations. Application of gauge field theory to describe deconfined spin liquid phase is treated. Topological quantum transitions, including those from small to large Fermi surface in the presence of van Hove singularities, are discussed.

Ferroelasticity in the LnNbO/sub 4/-type rare earth niobates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brixner, L.H.; Whitney, J.F.; Zumsteg, F.C.

1977-01-01

The previously reported phase transitions for the isostructural rare earth niobates between 500/sup 0/C and 850/sup 0/C correspond to a point group transformation 4/mF2/m, which is purely ferroelastic. The correct room temperature point group for all LnNbO/sub 4/ compounds is 2/m. Crystal growth and domain wall behavior is discussed for LaNbO/sub 4/. The high temperature phase transition is described for YbNbO/sub 4/.

Transit dosimetry in IMRT with an a-Si EPID in direct detection configuration

NASA Astrophysics Data System (ADS)

Sabet, Mahsheed; Rowshanfarzad, Pejman; Vial, Philip; Menk, Frederick W.; Greer, Peter B.

2012-08-01

In this study an amorphous silicon electronic portal imaging device (a-Si EPID) converted to direct detection configuration was investigated as a transit dosimeter for intensity modulated radiation therapy (IMRT). After calibration to dose and correction for a background offset signal, the EPID-measured absolute IMRT transit doses for 29 fields were compared to a MatriXX two-dimensional array of ionization chambers (as reference) using Gamma evaluation (3%, 3 mm). The MatriXX was first evaluated as reference for transit dosimetry. The accuracy of EPID measurements was also investigated by comparison of point dose measurements by an ionization chamber on the central axis with slab and anthropomorphic phantoms in a range of simple to complex fields. The uncertainty in ionization chamber measurements in IMRT fields was also investigated by its displacement from the central axis and comparison with the central axis measurements. Comparison of the absolute doses measured by the EPID and MatriXX with slab phantoms in IMRT fields showed that on average 96.4% and 97.5% of points had a Gamma index<1 in head and neck and prostate fields, respectively. For absolute dose comparisons with anthropomorphic phantoms, the values changed to an average of 93.6%, 93.7% and 94.4% of points with Gamma index<1 in head and neck, brain and prostate fields, respectively. Point doses measured by the EPID and ionization chamber were within 3% difference for all conditions. The deviations introduced in the response of the ionization chamber in IMRT fields were<1%. The direct EPID performance for transit dosimetry showed that it has the potential to perform accurate, efficient and comprehensive in vivo dosimetry for IMRT.

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

Müller, S. H.; Conway, G. D.; Birkenmeier, G.

A reciprocating Langmuir probe was used to directly measure the behavior of turbulence and flows in the X-point region during transitions between low-(L) and high-confinement (H) mode in ASDEX Upgrade. The probe traverses the divertor horizontally in 140 ms, typically 2–5 cm below the X-point. Toroidal Mach number, density, floating potential (ϕ{sub f}), and electron temperature (T{sub e}) are measured. In the regime accessible to the probe (P{sub inj}<1.5 MW, line-integrated core density <4×10{sup 19} m{sup −2}), the L-H transition features an intermediate phase (I-phase), characterized by limit-cycle oscillations at 0.5–3 kHz [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)]. The probe measurements revealmore » that this pulsing affects both the density and the toroidal Mach number. It is present in both the low-(LFS) and high-field sides (HFS) of the scrape-off layer, while high-amplitude broadband turbulence usually dominates the private-flux region. Profile comparisons between L-mode and I-phase show lower density in pulsing regions and small shifts in T{sub e}, directed oppositely on LFS and HFS, which are compensated by shifts in ϕ{sub f} to yield a surprisingly unchanged plasma potential profile. Directly observed L-I-phase transitions reveal that the onset of the pulsing is preceded by a fast 50% density drop in the HFS X-point region. Back transitions to L-mode occur essentially symmetrically, with the pulsing stopping first, followed by a fast recovery to L-mode density levels in the divertor.« less

Inelastic neutron scattering investigation of low temperature phase transition in Rb2ZnCl4 and K2ZnCl4

NASA Astrophysics Data System (ADS)

Quilichini, M.; Dvořák, V.; Boutrouille, P.

1991-09-01

Inelastic scattering of neutrons has revealed soft optic modes at the T point frac{1}{2}({b}^*+{c}^*) of the Brillouin zone both in Rb2ZnCl4 and K2ZnCl4 which are responsible for the phase transition from the ferroelectric to the lowest temperature phase of these materials. Moreover, in K2ZnCl4 near the T point a minimum on the soft optic branch in the direction (μ{b}^*+frac{1}{2}{c}^*) has been found which confirms the existence of a new incommensurate phase recently discovered by Gesi. The origin of this incommensurate phase is discussed from a phenomenological point of view and formulae for elastic constants are derived describing their behaviour near transition into incommensurate phase. Des mesures de diffusion inélastique des neutrons ont mis en évidence l'existence d'un mode optique mou au point T(frac{1}{2}({b}^*+{c}^*)) de la zone de Brillouin responsable de la transition de la phase ferroélectrique vers la phase basse température dans les deux composés Rb2ZnCl4 and K2ZnCl4. Pour K2ZnCl4 on montre que la branche optique molle présente un minimum au voisinage de T dans la direction (μ{b}^*+frac{1}{2}{c}^*), ce qui confirme l'existence de la nouvelle phase incommensurable récemment trouvée par Gesi. L'origine de cette phase est discutée sur la base d'un modèle phénoménologique dont on dérive aussi les formules des constantes élastiques et leur comportement au voisinage de la transition vers la phase incommensurable.

The multiuniverse transition in superfluid 3He

NASA Astrophysics Data System (ADS)

Bunkov, Yury

2013-10-01

The symmetry-breaking phase transitions of the universe and of superfluid 3He may lead to the formation of different states with different order parameters. In both cases the energy potential below the transition temperature has a complicated multidimensional profile with many local minima and saddle points, which correspond to different states. Consequently, not only topological defects, but also islands of different metastable states can be created. Using 3He we can analyse the properties and experimental consequences of such transitions and, in particular, the first-order phase transition between the two low symmetry states.

The multiuniverse transition in superfluid 3He.

PubMed

Bunkov, Yury

2013-10-09

The symmetry-breaking phase transitions of the universe and of superfluid (3)He may lead to the formation of different states with different order parameters. In both cases the energy potential below the transition temperature has a complicated multidimensional profile with many local minima and saddle points, which correspond to different states. Consequently, not only topological defects, but also islands of different metastable states can be created. Using (3)He we can analyse the properties and experimental consequences of such transitions and, in particular, the first-order phase transition between the two low symmetry states.

High-pressure phase transitions - Examples of classical predictability

NASA Astrophysics Data System (ADS)

Celebonovic, Vladan

1992-09-01

The applicability of the Savic and Kasanin (1962-1967) classical theory of dense matter to laboratory experiments requiring estimates of high-pressure phase transitions was examined by determining phase transition pressures for a set of 19 chemical substances (including elements, hydrocarbons, metal oxides, and salts) for which experimental data were available. A comparison between experimental and transition points and those predicted by the Savic-Kasanin theory showed that the theory can be used for estimating values of transition pressures. The results also support conclusions obtained in previous astronomical applications of the Savic-Kasanin theory.

The Kibble-Zurek mechanism in phase transitions of non-equilibrium systems

NASA Astrophysics Data System (ADS)

Cheung, Hil F. H.; Patil, Yogesh S.; Date, Aditya G.; Vengalattore, Mukund

2017-04-01

We experimentally realize a driven-dissipative phase transition using a mechanical parametric amplifier to demonstrate key signatures of a second order phase transition, including a point where the susceptibilities and relaxation time scales diverge, and where the system exhibits a spontaneous breaking of symmetry. Though reminiscent of conventional equilibrium phase transitions, it is unclear if such driven-dissipative phase transitions are amenable to the conventional Landau-Ginsburg-Wilson paradigm, which relies on concepts of scale invariance and universality, and recent work has shown that such phase transitions can indeed lie beyond such conventional universality classes. By quenching the system past the critical point, we investigate the dynamics of the emergent ordered phase and find that our measurements are in excellent agreement with the Kibble-Zurek mechanism. In addition to verifying the Kibble-Zurek hypothesis in driven-dissipative phase transitions for the first time, we also demonstrate that the measured critical exponents accurately reflect the interplay between intrinsic coherent dynamics and environmental correlations, showing a clear departure from mean field exponents in the case of non-Markovian system-bath interactions. We further discuss how reservoir engineering and the imposition of artificial environmental correlations can result in the stabilization of novel many-body quantum phases and aid in the creation of exotic non-equilibrium states of matter.

“Just another fish in the pond”: the transitional care experience of a hip fracture patient

PubMed Central

Toscan, Justine; Manderson, Brooke; Santi, Selena M; Stolee, Paul

2013-01-01

Introduction Miscommunication and lack of coordination can compromise care quality and patient safety during transitions in care, especially for medically complex older adults. Little research has been done to investigate care transitions from the perspective of those receiving and providing care. Methods This study explored multiple care transitions for an elderly hip fracture patient, post-surgery. Interviews and observations were conducted with the patient, their family caregivers, and health care providers, at each point of transition between four different care settings. Results Four key themes were identified over the patients care trajectory: ‘Missing Crucial Coversations’—Patient and family caregivers did not feel involved or informed about decisions in care; ‘Who’s Who’—Confusion about the role of health care providers; ‘Ready or Not’—Not knowing what to expect or what is expected; and, ‘Playing by the Rules’—Health system policies and procedures hinder individualized care. Conclusion Study findings point to the need for the health care system to engage patients and family caregivers more fully and consistently in the process of care transitions as well as the importance of understanding these processes from multiple perspectives. Recommendations for system integration are proposed with a focus on transitional care. PMID:23882170

78 FR 9866 - Special Local Regulation; Moss Point Rockin' the Riverfront Festival; Robertson Lake & O'Leary...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-12

... 1625-AA08 Special Local Regulation; Moss Point Rockin' the Riverfront Festival; Robertson Lake & O... Riverfront Festival high speed boat races. Entry into, transiting or anchoring in this area is prohibited to... Point Rockin' the Riverfront Festival; Robertson Lake & O'Leary Lake; Moss Point, MS. (a) Location. The...

Phase transitions in single macromolecules: Loop-stretch transition versus loop adsorption transition in end-grafted polymer chains

NASA Astrophysics Data System (ADS)

Zhang, Shuangshuang; Qi, Shuanhu; Klushin, Leonid I.; Skvortsov, Alexander M.; Yan, Dadong; Schmid, Friederike

2018-01-01

We use Brownian dynamics simulations and analytical theory to compare two prominent types of single molecule transitions. One is the adsorption transition of a loop (a chain with two ends bound to an attractive substrate) driven by an attraction parameter ɛ and the other is the loop-stretch transition in a chain with one end attached to a repulsive substrate, driven by an external end-force F applied to the free end. Specifically, we compare the behavior of the respective order parameters of the transitions, i.e., the mean number of surface contacts in the case of the adsorption transition and the mean position of the chain end in the case of the loop-stretch transition. Close to the transition points, both the static behavior and the dynamic behavior of chains with different length N are very well described by a scaling ansatz with the scaling parameters (ɛ - ɛ*)Nϕ (adsorption transition) and (F - F*)Nν (loop-stretch transition), respectively, where ϕ is the crossover exponent of the adsorption transition and ν is the Flory exponent. We show that both the loop-stretch and the loop adsorption transitions provide an exceptional opportunity to construct explicit analytical expressions for the crossover functions which perfectly describe all simulation results on static properties in the finite-size scaling regime. Explicit crossover functions are based on the ansatz for the analytical form of the order parameter distributions at the respective transition points. In contrast to the close similarity in equilibrium static behavior, the dynamic relaxation at the two transitions shows qualitative differences, especially in the strongly ordered regimes. This is attributed to the fact that the surface contact dynamics in a strongly adsorbed chain is governed by local processes, whereas the end height relaxation of a strongly stretched chain involves the full spectrum of Rouse modes.

Brake Lining for Transit Buses - Bonded vs. Bolted

DOT National Transportation Integrated Search

1985-06-01

This report points out an often cited complaint from urban transit agencies concerning the Advanced Design Bus: the relatively short brake lining life. Despite design improvements made by the equipment supply industry since the introduction of the AD...

Transitions and Trajectories from Higher Education to Work and Back--A Comparison between Finnish and Portuguese Graduates

ERIC Educational Resources Information Center

Alves, Mariana Gaio; Korhonen, Vesa

2016-01-01

There is growing evidence that transitions from education to work (and from work to education) can take place several times and occur at different points in an individual's life cycle. This paper's overall intention is to contribute to a deeper understanding of higher education graduates' transitions between education and work shortly after…

Children's Transitions to School: "So What about the Parents?" or "So, What about the Parents?"

ERIC Educational Resources Information Center

Webb, Grant; Knight, Bruce Allen; Busch, Gillian

2017-01-01

Children progress through a number of life transitions and each is a pivotal point of development and growth for them, their parents and family members. Through a review of the literature, the Bioecological Model will be used to frame childhood transitions as highly social, contextualised and political. This paper will assert that governments,…

Where is the continuum in lattice quantum chromodynamics?

NASA Technical Reports Server (NTRS)

Kennedy, A. D.; Pendleton, B. J.; Kuti, J.; Meyer, S.

1985-01-01

A Monte Carlo calculation of the quark-liberating phase transition in lattice quantum chromodynamics is presented. The transition temperature as a function of the lattice coupling g does not scale according to the perturbative beta function for 6/g-squared less than 6.1. Finite-size scaling is used in analyzing the properties of the lattice system near the transition point.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Filippone, Michele; Dusuel, Sebastien; Vidal, Julien

We consider a set of fully connected spin models that display first- or second-order transitions and for which we compute the ground-state entanglement in the thermodynamical limit. We analyze several entanglement measures (concurrence, Renyi entropy, and negativity) and show that, in general, discontinuous transitions lead to a jump of these quantities at the transition point. Interestingly, we also find examples where this is not the case.

The School/Work Nexus: Transition of Youth from School to Work.

ERIC Educational Resources Information Center

Ginzberg, Eli

This monograph by educator-philosopher Eli Ginzberg, commisioned by the Phi Delta Kappa Educational Foundation, examines the transition from school to work, exploring why the transition is so hard for some groups of young people, relatively easy for others. The point of the book is not to add one more research report to the literature dealing with…

A Quantitative Comparative Analysis of Ninth Grade Academies and Graduation Rates in Texas High Schools

ERIC Educational Resources Information Center

Lyons, Guy Kevin

2014-01-01

Students face many challenges in the transition to high school. From pressures of high-stakes testing for graduation to transitioning to the high school environment, many diversions can delay or even stop a student's path to graduation. Ninth-grade students are at a pivotal point in their educational careers, and a successful transition to high…

Alcohol Use during the Transition from Middle School to High School: National Panel Data on Prevalence and Moderators

ERIC Educational Resources Information Center

Jackson, Kristina M.; Schulenberg, John E.

2013-01-01

The movement from middle school to high school is a normative transition that is typically associated with increased stress and opportunity in social and academic domains. Theoretically, this transition may reflect a turning point in terms of initiating or sharply increasing heavy alcohol use, a notion that has received little attention in the…

Railroad special investigation report : Maryland Transit Administration light rail vehicle accidents at the Baltimore-Washington International Airport transit station near Baltimore, Maryland, February 13 and August 15, 2000

DOT National Transportation Integrated Search

2001-12-11

In 2000, the Maryland Transit Administration experienced two similar accidents in the same location just 6 months apart. Both accidents involved the failure of a light rail vehicle train to stop at the designated stopping point at the Baltimore-Washi...

Nontrivial transition of transmission in a highly open quantum point contact in the quantum Hall regime

NASA Astrophysics Data System (ADS)

Hong, Changki; Park, Jinhong; Chung, Yunchul; Choi, Hyungkook; Umansky, Vladimir

2017-11-01

Transmission through a quantum point contact (QPC) in the quantum Hall regime usually exhibits multiple resonances as a function of gate voltage and high nonlinearity in bias. Such behavior is unpredictable and changes sample by sample. Here, we report the observation of a sharp transition of the transmission through an open QPC at finite bias, which was observed consistently for all the tested QPCs. It is found that the bias dependence of the transition can be fitted to the Fermi-Dirac distribution function through universal scaling. The fitted temperature matches quite nicely to the electron temperature measured via shot-noise thermometry. While the origin of the transition is unclear, we propose a phenomenological model based on our experimental results that may help to understand such a sharp transition. Similar transitions are observed in the fractional quantum Hall regime, and it is found that the temperature of the system can be measured by rescaling the quasiparticle energy with the effective charge (e*=e /3 ). We believe that the observed phenomena can be exploited as a tool for measuring the electron temperature of the system and for studying the quasiparticle charges of the fractional quantum Hall states.

Phase Diagrams and the Non-Linear Dielectric Constant in the Landau-Type Potential Including the Linear-Quadratic Coupling between Order Parameters

NASA Astrophysics Data System (ADS)

Iwata, Makoto; Orihara, Hiroshi; Ishibashi, Yoshihiro

1997-04-01

The phase diagrams in the Landau-type thermodynamic potential including the linear-quadratic coupling between order parameters p and q, i.e., qp2, which is applicable to the phase transition in the benzil, phospholipid bilayers, and the isotropic-nematic phase transition in liquid crystals, are studied. It was found that the phase diagram in the extreme case has one tricritical point c1, one critical end point e1, and two triple points t1 and t2. The linear and nonlinear dielectric constants in the potential are discussed in the case that the order parameter p is the polarization.

Predicting Transition from Laminar to Turbulent Flow over a Surface

NASA Technical Reports Server (NTRS)

Rajnarayan, Dev (Inventor); Sturdza, Peter (Inventor)

2016-01-01

A prediction of whether a point on a computer-generated surface is adjacent to laminar or turbulent flow is made using a transition prediction technique. A plurality of instability modes are obtained, each defined by one or more mode parameters. A vector of regressor weights is obtained for the known instability growth rates in a training dataset. For an instability mode in the plurality of instability modes, a covariance vector is determined. A predicted local instability growth rate at the point is determined using the covariance vector and the vector of regressor weights. Based on the predicted local instability growth rate, an n-factor envelope at the point is determined.

Nonequilibrium Tricritical Point in a System with Long-Range Interactions

NASA Astrophysics Data System (ADS)

Antoniazzi, Andrea; Fanelli, Duccio; Ruffo, Stefano; Yamaguchi, Yoshiyuki Y.

2007-07-01

Systems with long-range interactions display a short-time relaxation towards quasistationary states whose lifetime increases with system size. With reference to the Hamiltonian mean field model, we here show that a maximum entropy principle, based on Lynden-Bell’s pioneering idea of “violent relaxation,” predicts the presence of out-of-equilibrium phase transitions separating the relaxation towards homogeneous (zero magnetization) or inhomogeneous (nonzero magnetization) quasistationary states. When varying the initial condition within a family of “water bags” with different initial magnetization and energy, first- and second-order phase transition lines are found that merge at an out-of-equilibrium tricritical point. Metastability is theoretically predicted and numerically checked around the first-order phase transition line.

Photon orbits and thermodynamic phase transition of d -dimensional charged AdS black holes

NASA Astrophysics Data System (ADS)

Wei, Shao-Wen; Liu, Yu-Xiao

2018-05-01

We study the relationship between the null geodesics and thermodynamic phase transition for the charged AdS black hole. In the reduced parameter space, we find that there exist nonmonotonic behaviors of the photon sphere radius and the minimum impact parameter for the pressure below its critical value. The study also shows that the changes of the photon sphere radius and the minimum impact parameter can serve as order parameters for the small-large black hole phase transition. In particular, these changes have an universal exponent of 1/2 near the critical point for any dimension d of spacetime. These results imply that there may exist universal critical behavior of gravity near the thermodynamic critical point of the black hole system.

Metastable Distributions of Markov Chains with Rare Transitions

NASA Astrophysics Data System (ADS)

Freidlin, M.; Koralov, L.

2017-06-01

In this paper we consider Markov chains X^\\varepsilon _t with transition rates that depend on a small parameter \\varepsilon . We are interested in the long time behavior of X^\\varepsilon _t at various \\varepsilon -dependent time scales t = t(\\varepsilon ). The asymptotic behavior depends on how the point (1/\\varepsilon , t(\\varepsilon )) approaches infinity. We introduce a general notion of complete asymptotic regularity (a certain asymptotic relation between the ratios of transition rates), which ensures the existence of the metastable distribution for each initial point and a given time scale t(\\varepsilon ). The technique of i-graphs allows one to describe the metastable distribution explicitly. The result may be viewed as a generalization of the ergodic theorem to the case of parameter-dependent Markov chains.

Silent initial conditions for cosmological perturbations with a change of spacetime signature

NASA Astrophysics Data System (ADS)

Mielczarek, Jakub; Linsefors, Linda; Barrau, Aurelien

Recent calculations in loop quantum cosmology suggest that a transition from a Lorentzian to a Euclidean spacetime might take place in the very early universe. The transition point leads to a state of silence, characterized by a vanishing speed of light. This behavior can be interpreted as a decoupling of different space points, similar to the one characterizing the BKL phase. In this study, we address the issue of imposing initial conditions for the cosmological perturbations at the transition point between the Lorentzian and Euclidean phases. Motivated by the decoupling of space points, initial conditions characterized by a lack of correlations are investigated. We show that the “white noise” gains some support from analysis of the vacuum state in the deep Euclidean regime. Furthermore, the possibility of imposing the silent initial conditions at the trans-Planckian surface, characterized by a vanishing speed for the propagation of modes with wavelengths of the order of the Planck length, is studied. Such initial conditions might result from the loop deformations of the Poincaré algebra. The conversion of the silent initial power spectrum to a scale-invariant one is also examined.

A Point Spread Function for the EPOXI Mission

NASA Technical Reports Server (NTRS)

Barry, Richard K.

2010-01-01

The Extrasolar Planet Observation Characterization and the Deep Impact Extended Investigation missions (EPOXI) are currently observing the transits of exoplanets, two comet nuclei at short range, and the Earth and Mars using the High Resolution Instrument (HRI) - a 0.3 m f/35 telescope on the Deep Impact probe. The HRI is in a permanently defocused state with the instrument pOint of focus about 0.6 cm before the focal plane due to the use of a reference flat mirror that took a power during ground thermal-vacuum testing. Consequently, the point spread function (PSF) covers approximately nine pixels FWHM and is characterized by a patch with three-fold symmetry due to the three-point support structures of the primary and secondary mirrors. The PSF is also strongly color dependent varying in shape and size with change in filtration and target color. While defocus is highly desirable for exoplanet transit observations to limit sensitivity to intra-pixel variation, it is suboptimal for observations of spatially resolved targets. Consequently, all images used in our analysis of such objects were deconvolved with an instrument PSF. The instrument PSF is also being used to optimize transit analysis. We discuss development and usage of an instrument PSF for these observations.

Extrapolation of radiation thermometry scales for determining the transition temperature of metal-carbon points. Experiments with the Co-C

NASA Astrophysics Data System (ADS)

Battuello, M.; Girard, F.; Florio, M.

2009-02-01

Four independent radiation temperature scales approximating the ITS-90 at 900 nm, 950 nm and 1.6 µm have been realized from the indium point (429.7485 K) to the copper point (1357.77 K) which were used to derive by extrapolation the transition temperature T90(Co-C) of the cobalt-carbon eutectic fixed point. An INRIM cell was investigated and an average value T90(Co-C) = 1597.20 K was found with the four values lying within 0.25 K. Alternatively, thermodynamic approximated scales were realized by assigning to the fixed points the best presently available thermodynamic values and deriving T(Co-C). An average value of 1597.27 K was found (four values lying within 0.25 K). The standard uncertainties associated with T90(Co-C) and T(Co-C) were 0.16 K and 0.17 K, respectively. INRIM determinations are compatible with recent thermodynamic determinations on three different cells (values lying between 1597.11 K and 1597.25 K) and with the result of a comparison on the same cell by an absolute radiation thermometer and an irradiance measurement with filter radiometers which give values of 1597.11 K and 1597.43 K, respectively (Anhalt et al 2006 Metrologia 43 S78-83). The INRIM approach allows the determination of both ITS-90 and thermodynamic temperature of a fixed point in a simple way and can provide valuable support to absolute radiometric methods in defining the transition temperature of new high-temperature fixed points.

α-flips and T-points in the Lorenz system

NASA Astrophysics Data System (ADS)

Creaser, Jennifer L.; Krauskopf, Bernd; Osinga, Hinke M.

2015-03-01

We consider the Lorenz system near the classic parameter regime and study the phenomenon we call an α-flip. An α-flip is a transition where the one-dimensional stable manifolds Ws(p±) of two secondary equilibria p± undergo a sudden transition in terms of the direction from which they approach p±. This is a bifurcation at infinity and does not involve an invariant object in phase space. This fact was discovered by Sparrow in the 1980s but the stages of the transition could not be calculated and the phenomenon was not well understood (Sparrow 1982 The Lorenz equations (New York: Springer)). Here we employ a boundary value problem set-up and use pseudo-arclength continuation in AUTO to follow this sudden transition of Ws(p±) as a continuous family of orbit segments. In this way, we geometrically characterize and determine the moment of the actual α-flip. We also investigate how the α-flip takes place relative to the two-dimensional stable manifold of the origin, which shows no apparent topological change before or after the α-flip. Our approach allows for easy detection and subsequent two-parameter continuation of the first and further α-flips. We illustrate this for the first 25 α-flips and find that they end at terminal points, or T-points, where there is a heteroclinic connection from the secondary equilibria to the origin. It turns out that α-flips must occur naturally near T-points. We find scaling relations for the α-flips and T-points that allow us to predict further such bifurcations and to improve the efficiency of our computations.

Low temperature synthesis of LnOF rare-earth oxyfluorides through reaction of the oxides with PTFE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dutton, S.E., E-mail: sdutton@princeton.edu; Hirai, D.; Cava, R.J.

2012-03-15

Highlights: Black-Right-Pointing-Pointer Low temperature synthesis of LnOF rare-earth oxyfluorides from Ln{sub 2}O{sub 3} and PTFE (CF{sub 2}). Black-Right-Pointing-Pointer Rhombohedral LnOF is the major phase and forms as nanocrystals, 29-103 nm. Black-Right-Pointing-Pointer Expected lanthanide contraction observed in lattice parameters and bond lengths. Black-Right-Pointing-Pointer TbOF orders antiferromagnetically at 10 K and has a metamagnetic transition at 1.8 T. Black-Right-Pointing-Pointer GdOF orders antiferromagnetically at 5 K, other LnOF are paramagnetic. -- Abstract: A low temperature solid-state synthesis route, employing polytetrafluoroethylene (PTFE) and the rare-earth oxides, for the formation of the LnOF rare-earth oxyfluorides (Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Tb,more » Dy, Ho, Er), is reported. With the exception of LaOF, which forms in a tetragonal variant, rhomobohedral LnOF is found to be the major product of the reaction. In the case of PrOF, a transition from the rhombohedral to the cubic fluorite phase is observed on heating in air to 500 Degree-Sign C. X-ray diffraction shows the expected lanthanide contraction in the lattice parameters and bond lengths. Magnetic susceptibility measurements show antiferromagnetic-like ordering in TbOF, T{sub m} = 10 K, with a metamagnetic transition at a field {mu}{sub 0}H{sub t} = 1.8 T at 2 K. An antiferromagnetic transition, T{sub N} = 4 K, is observed in GdOF. Paramagnetic behavior is observed above 2 K in PrOF, NdOF, DyOF, HoOF and ErOF. The magnetic susceptibility of EuOF is characteristic of Van Vleck paramagnetism.« less

Nonequilibrium transitions in complex networks: A model of social interaction

NASA Astrophysics Data System (ADS)

Klemm, Konstantin; Eguíluz, Víctor M.; Toral, Raúl; San Miguel, Maxi

2003-02-01

We analyze the nonequilibrium order-disorder transition of Axelrod’s model of social interaction in several complex networks. In a small-world network, we find a transition between an ordered homogeneous state and a disordered state. The transition point is shifted by the degree of spatial disorder of the underlying network, the network disorder favoring ordered configurations. In random scale-free networks the transition is only observed for finite size systems, showing system size scaling, while in the thermodynamic limit only ordered configurations are always obtained. Thus, in the thermodynamic limit the transition disappears. However, in structured scale-free networks, the phase transition between an ordered and a disordered phase is restored.

Dynamical instability of a spin spiral in an interacting Fermi gas as a probe of the Stoner transition

NASA Astrophysics Data System (ADS)

Conduit, G. J.; Altman, E.

2010-10-01

We propose an experiment to probe ferromagnetic phenomena in an ultracold Fermi gas, while alleviating the sensitivity to three-body loss and competing many-body instabilities. The system is initialized in a small pitch spin spiral, which becomes unstable in the presence of repulsive interactions. To linear order the exponentially growing collective modes exhibit critical slowing down close to the Stoner transition point. Also, to this order, the dynamics are identical on the paramagnetic and ferromagnetic sides of the transition. However, we show that scattering off the exponentially growing modes qualitatively alters the collective mode structure. The critical slowing down is eliminated and in its place a new unstable branch develops at large wave vectors. Furthermore, long-wavelength instabilities are quenched on the paramagnetic side of the transition. We study the experimental observation of the instabilities, specifically addressing the trapping geometry and how phase-contrast imaging will reveal the emerging domain structure. These probes of the dynamical phenomena could allow experiments to detect the transition point and distinguish between the paramagnetic and ferromagnetic regimes.

Radiated interference in rapid transit systems. volume 2. suggested test procedures.

DOT National Transportation Integrated Search

1987-06-30

The purpose of this report is to present a suggested test procedure for measuring the radiated electromagnetic interference (EMI) emanating from rail transit systems. This report points out that, unlike inductive and conductive EMI, radiated EMI has ...

76 FR 31230 - Vessel Traffic Service Lower Mississippi River; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-31

... Area. B Industrial Canal..... 92.7 AHP 29[deg]57.2' N; Upbound transiting 90[deg]01.68' W. Algiers...; Downbound transiting (Naval Ships). 90[deg]05.87' W. Algiers Point Special Area. E Huey P Long Bridge... 106...

Holographic Van der Waals phase transition of the higher-dimensional electrically charged hairy black hole

NASA Astrophysics Data System (ADS)

Li, Hui-Ling; Feng, Zhong-Wen; Zu, Xiao-Tao

2018-01-01

With motivation by holography, employing black hole entropy, two-point connection function and entanglement entropy, we show that, for the higher-dimensional Anti-de Sitter charged hairy black hole in the fixed charged ensemble, a Van der Waals-like phase transition can be observed. Furthermore, based on the Maxwell equal-area construction, we check numerically the equal-area law for a first order phase transition in order to further characterize the Van der Waals-like phase transition.

Metal Carbon Eutectics to Extend the Use of the Fixed-Point Technique in Precision IR Thermometry

NASA Astrophysics Data System (ADS)

Battuello, M.; Girard, F.; Florio, M.

2008-06-01

The high-temperature extension of the fixed-point technique for primary calibration of precision infrared (IR) thermometers was investigated both through mathematical simulations and laboratory investigations. Simulations were performed with Co C (1,324°C) and Pd C (1, 492°C) eutectic fixed points, and a precision IR thermometer was calibrated from the In point (156.5985°C) up to the Co C point. Mathematical simulations suggested the possibility of directly deriving the transition temperature of the Co C and Pd C points by extrapolating the calibration derived from fixed-point measurements from In to the Cu point. Both temperatures, as a result of the low uncertainty associated with the In Cu calibration and the high number of fixed points involved in the calibration process, can be derived with an uncertainty of 0.11°C for Co C and 0.18°C for Pd C. A transition temperature of 1,324.3°C for Co C was determined from the experimental verification, a value higher than, but compatible with, the one proposed by the thermometry community for inclusion as a secondary reference point for ITS-90 dissemination, i.e., 1,324.0°C.

Collapsing lattice animals and lattice trees in two dimensions

NASA Astrophysics Data System (ADS)

Hsu, Hsiao-Ping; Grassberger, Peter

2005-06-01

We present high statistics simulations of weighted lattice bond animals and lattice trees on the square lattice, with fugacities for each non-bonded contact and for each bond between two neighbouring monomers. The simulations are performed using a newly developed sequential sampling method with resampling, very similar to the pruned-enriched Rosenbluth method (PERM) used for linear chain polymers. We determine with high precision the line of second-order transitions from an extended to a collapsed phase in the resulting two-dimensional phase diagram. This line includes critical bond percolation as a multicritical point, and we verify that this point divides the line into different universality classes. One of them corresponds to the collapse driven by contacts and includes the collapse of (weakly embeddable) trees. There is some evidence that the other is subdivided again into two parts with different universality classes. One of these (at the far side from collapsing trees) is bond driven and is represented by the Derrida-Herrmann model of animals having bonds only (no contacts). Between the critical percolation point and this bond-driven collapse seems to be an intermediate regime, whose other end point is a multicritical point P* where a transition line between two collapsed phases (one bond driven and the other contact driven) sparks off. This point P* seems to be attractive (in the renormalization group sense) from the side of the intermediate regime, so there are four universality classes on the transition line (collapsing trees, critical percolation, intermediate regime, and Derrida-Herrmann). We obtain very precise estimates for all critical exponents for collapsing trees. It is already harder to estimate the critical exponents for the intermediate regime. Finally, it is very difficult to obtain with our method good estimates of the critical parameters of the Derrida-Herrmann universality class. As regards the bond-driven to contact-driven transition in the collapsed phase, we have some evidence for its existence and rough location, but no precise estimates of critical exponents.

Technology, Incentives, or Both? Factors Related to Level of Hospital Health Information Exchange.

PubMed

Lin, Sunny C; Everson, Jordan; Adler-Milstein, Julia

2018-02-28

To assess whether the level of health information exchange (HIE) in U.S. hospitals is related to technology capabilities, incentives to exchange, or both. A total of 1,812 hospitals attesting to stage 2 of Medicare's Meaningful Use Incentive Program through April 2016. Hospital-level, multivariate OLS regression with state fixed effects was used to analyze the relationship between technology capability and incentives measures, and percent of care transitions with summary of care records (SCRs) sent electronically to subsequent providers. Stage 2 hospitals reported sending SCRs electronically for an average of 41 percent (median = 33 percent) of transitions. HIE level is related to four capability measures, one incentive measure, and one measure that is related to both capability and incentive. Percent of transitions with SCRs sent electronically was 3 percentage points higher (95 percent CI: 0.1-5.1) for hospitals with a third-party HIE vendor, 3 percentage points higher (95 percent CI: 0.5-5.4) for hospitals with an EHR vendor as their HIE vendor, and 3 percentage points higher (95 percent CI: 0.4-5.4) for hospitals that automatically alert primary care providers. The direction and statistical significance of the relationships between specific EHR vendor and electronic SCR transmission level varied by vendor. Nonprofits and government hospitals performed 5 percentage points higher (95 percent CI: 1.5-9.1) and 8 percentage points higher (95 percent CI: 3.4-12.3) than for-profits. Hospitals in systems performed 3 percentage points higher (95 percent CI: 0.8-6.1). The overall level of HIE is low, with hospitals sending an SCR electronically for less than half of patient transitions. Specific hospital characteristics related to both technology capabilities and incentives were associated with higher levels of HIE. © Health Research and Educational Trust.

Transitions and Turning Points: Exploring How First-in-Family Female Students Story Their Transition to University and Student Identity Formation

ERIC Educational Resources Information Center

O'Shea, Sarah

2014-01-01

The purpose of this article is to explore how one group of students reflect upon their transition into the higher education environment. This qualitative research project followed one group of female undergraduate students as they moved through the first year of study. All of the participants were the first in their family to consider further…

Relationship between longitudinal stress wave transit time and moisture content of lumber during kiln-drying

Treesearch

William T. Simpson; Xiping. Wang

2001-01-01

The relationship between longitudinal stress wave transit time and wood moisture content (MC) was examined as a potential means of estimating MC control points in dry kiln schedules for lumber. A linear relationship was found between the relative transit time and the average MC of sugar maple and ponderosa pine boards dried according to typical kiln schedules.

Formational Turning Points in the Transition to College: Understanding How Communication Events Shape First-Generation Students' Pedagogical and Interpersonal Relationships with Their College Teachers

ERIC Educational Resources Information Center

Wang, Tiffany R.

2014-01-01

In the present study, I explored student-teacher interaction, student-teacher relationship formation and development, and the ways in which student-teacher interaction and relationships facilitated support and persistence for first-generation (FG) students during the transition to college. Using transition theory as a sensitizing framework, I took…

The E(2) symmetry and quantum phase transition in the two-dimensional limit of the vibron model

NASA Astrophysics Data System (ADS)

Zhang, Yu; Pan, Feng; Liu, Yu-Xin; Draayer, J. P.

2010-11-01

We study in detail the relation between the two-dimensional Euclidean dynamical E(2) symmetry and the quantum phase transition in the two-dimensional limit of the vibron model, called the U(3) vibron model. Both geometric and algebraic descriptions of the U(3) vibron model show that structures of low-lying states at the critical point of the model with a quartic potential as its classical limit can be approximately described by the E(2) symmetry. We also fit the finite-size scaling exponent of the energy levels and E1 transition rates in the F(2) model, which is exactly the E(2) model but with truncation in its Hilbert subspace, as well as those at the critical point in the U(3) vibron model. The N-scaling power law around the critical point shows that the E(2) symmetry is well preserved even for cases with finite number of bosons. In addition, two kinds of experimentally accessible effective order parameters, such as the energy ratios E_{2_1}/E_{1_1}, E_{3_1}/E_{1_1} and E1 transition ratios \\frac{B(E1;2_1\\rightarrow 1_1)}{B(E1;1_1\\rightarrow 0_1)}, \\frac{B(E1;0_2\\rightarrow 1_1)}{B(E1;1_1\\rightarrow 0_1)}, are proposed to identify the second-order phase transition in such systems. Possible empirical examples exhibiting approximate E(2) symmetry are also presented.

Analytical studies on holographic superconductor in the probe limit

NASA Astrophysics Data System (ADS)

Peng, Yan; Liu, Guohua

2017-09-01

We investigate the holographic superconductor model constructed in the (2+1)-dimensional AdS soliton background in the probe limit. With analytical methods, we obtain the formula of critical phase transition points with respect to the scalar mass. We also generalize this formula to higher-dimensional space-time. We mention that these formulas are precise compared to numerical results. In addition, we find a correspondence between the value of the charged scalar field at the tip and the scalar operator at infinity around the phase transition points.

Critical behavior of modulus of gel

NASA Astrophysics Data System (ADS)

Tokita, Masayuki; Niki, Ryoya; Hikichi, Kunio

1985-09-01

The critical behavior of the shear modulus of casein gel is studied. The shear modulus of casein gel scales with the conductivity exponent in the immediate vicinity of the sol-gel transition point. The asymptotic behavior of the modulus in the region far above the transition point is governed by a different exponent which is much larger than the conductivity exponent. These results are explainable by the crossover behavior of the percolation process. This study shows that the gelation of the casein micelle solution is a realization of the percolation process.

The existence of negative absolute temperatures in Axelrod’s social influence model

NASA Astrophysics Data System (ADS)

Villegas-Febres, J. C.; Olivares-Rivas, W.

2008-06-01

We introduce the concept of temperature as an order parameter in the standard Axelrod’s social influence model. It is defined as the relation between suitably defined entropy and energy functions, T=(. We show that at the critical point, where the order/disorder transition occurs, this absolute temperature changes in sign. At this point, which corresponds to the transition homogeneous/heterogeneous culture, the entropy of the system shows a maximum. We discuss the relationship between the temperature and other properties of the model in terms of cultural traits.

Internal character dictates transition dynamics between isolation and cohesive grouping

NASA Astrophysics Data System (ADS)

Manrique, Pedro D.; Hui, Pak Ming; Johnson, Neil F.

2015-12-01

We show that accounting for internal character among interacting heterogeneous entities generates rich transition behavior between isolation and cohesive dynamical grouping. Our analytical and numerical calculations reveal different critical points arising for different character-dependent grouping mechanisms. These critical points move in opposite directions as the population's diversity decreases. Our analytical theory may help explain why a particular class of universality is so common in the real world, despite the fundamental differences in the underlying entities. It also correctly predicts the nonmonotonic temporal variation in connectivity observed recently in one such system.

Planetary Transits of the Trans-Atlantic Exoplanet Survey Candidate TrES-1b

NASA Astrophysics Data System (ADS)

Price, A.; Bissinger, R.; Laughlin, G. P.; Gary, B. L.; Vanmunster, T.; Henden, A. A.; Starkey, D. R.; Kaiser, D. H.; Holtzman, J. A.; Marschall, L. A.; Michalik, T.; Wellington, T.; Paakkonen, P.

2005-08-01

The AAVSO compiled 10,560 CCD observations of the suspected exoplanet transit object TrES-1b covering seven complete transit windows, three windows of partial coverage, and coverage of baseline non-transit periods. Visual inspection of the light curves reveals the presence of slight humps at the egress points of some transits. A boot strap Monte Carlo simulation was applied to the data to confirm that the humps exist to a statistically significant degree. However, it does not rule out systemic effects which will be tested with campaigns in the 2005 observing season.

In situ observation of sol-gel transition of agarose aqueous solution by fluorescence measurement.

PubMed

Wang, Zheng; Yang, Kun; Li, Haining; Yuan, Chaosheng; Zhu, Xiang; Huang, Haijun; Wang, Yongqiang; Su, Lei; Fang, Yapeng

2018-06-01

Sol-gel transition behavior of agarose aqueous solution was investigated by using rheology and fluorescence measurement. On heating, the storage modulus G' decreased gradually, then deviated abruptly at the temperature of about 65°C, and finally decreased slowly again. For fluorescence measurement, the phase transition point kept almost at the temperature of 65°C, which was consistent with that in rheology measurement. Upon compression, it was indicated that the fluorescence lifetime for the probe in the agarose aqueous solution showed a dramatic change in the vicinity of the phase transition point. T vs. P phase diagram of agarose aqueous solution was constructed, which showed that the melting point was an increasing function of pressure. Based on the phase diagram, the agarose gels were prepared by cooling under atmospheric pressure and the pressure of 300MPa, respectively. From the result of the recovered samples studied by optical rheometry, it was found that agarose gel prepared under high pressure had a higher elasticity and lower viscosity index, compared with that under atmospheric pressure. It could be speculated that such kinds of properties might be attributed to the smaller pore size during gelation under high pressure. Copyright © 2018. Published by Elsevier B.V.

Predicting changes in hypertension control using electronic health records from a chronic disease management program

PubMed Central

Sun, Jimeng; McNaughton, Candace D; Zhang, Ping; Perer, Adam; Gkoulalas-Divanis, Aris; Denny, Joshua C; Kirby, Jacqueline; Lasko, Thomas; Saip, Alexander; Malin, Bradley A

2014-01-01

Objective Common chronic diseases such as hypertension are costly and difficult to manage. Our ultimate goal is to use data from electronic health records to predict the risk and timing of deterioration in hypertension control. Towards this goal, this work predicts the transition points at which hypertension is brought into, as well as pushed out of, control. Method In a cohort of 1294 patients with hypertension enrolled in a chronic disease management program at the Vanderbilt University Medical Center, patients are modeled as an array of features derived from the clinical domain over time, which are distilled into a core set using an information gain criteria regarding their predictive performance. A model for transition point prediction was then computed using a random forest classifier. Results The most predictive features for transitions in hypertension control status included hypertension assessment patterns, comorbid diagnoses, procedures and medication history. The final random forest model achieved a c-statistic of 0.836 (95% CI 0.830 to 0.842) and an accuracy of 0.773 (95% CI 0.766 to 0.780). Conclusions This study achieved accurate prediction of transition points of hypertension control status, an important first step in the long-term goal of developing personalized hypertension management plans. PMID:24045907

Apparent Transition Behavior of Widely-Used Turbulence Models

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.

2006-01-01

The Spalart-Allmaras and the Menter SST kappa-omega turbulence models are shown to have the undesirable characteristic that, for fully turbulent computations, a transition region can occur whose extent varies with grid density. Extremely fine two-dimensional grids over the front portion of an airfoil are used to demonstrate the effect. As the grid density is increased, the laminar region near the nose becomes larger. In the Spalart-Allmaras model this behavior is due to convergence to a laminar-behavior fixed point that occurs in practice when freestream turbulence is below some threshold. It is the result of a feature purposefully added to the original model in conjunction with a special trip function. This degenerate fixed point can also cause nonuniqueness regarding where transition initiates on a given grid. Consistent fully turbulent results can easily be achieved by either using a higher freestream turbulence level or by making a simple change to one of the model constants. Two-equation kappa-omega models, including the SST model, exhibit strong sensitivity to numerical resolution near the area where turbulence initiates. Thus, inconsistent apparent transition behavior with grid refinement in this case does not appear to stem from the presence of a degenerate fixed point. Rather, it is a fundamental property of the kappa-omega model itself, and is not easily remedied.

Predicting changes in hypertension control using electronic health records from a chronic disease management program.

PubMed

Sun, Jimeng; McNaughton, Candace D; Zhang, Ping; Perer, Adam; Gkoulalas-Divanis, Aris; Denny, Joshua C; Kirby, Jacqueline; Lasko, Thomas; Saip, Alexander; Malin, Bradley A

2014-01-01

Common chronic diseases such as hypertension are costly and difficult to manage. Our ultimate goal is to use data from electronic health records to predict the risk and timing of deterioration in hypertension control. Towards this goal, this work predicts the transition points at which hypertension is brought into, as well as pushed out of, control. In a cohort of 1294 patients with hypertension enrolled in a chronic disease management program at the Vanderbilt University Medical Center, patients are modeled as an array of features derived from the clinical domain over time, which are distilled into a core set using an information gain criteria regarding their predictive performance. A model for transition point prediction was then computed using a random forest classifier. The most predictive features for transitions in hypertension control status included hypertension assessment patterns, comorbid diagnoses, procedures and medication history. The final random forest model achieved a c-statistic of 0.836 (95% CI 0.830 to 0.842) and an accuracy of 0.773 (95% CI 0.766 to 0.780). This study achieved accurate prediction of transition points of hypertension control status, an important first step in the long-term goal of developing personalized hypertension management plans.

Apparent Transition Behavior of Widely-Used Turbulence Models

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.

2007-01-01

The Spalart-Allmaras and the Menter SST k-omega turbulence models are shown to have the undesirable characteristic that, for fully turbulent computations, a transition region can occur whose extent varies with grid density. Extremely fine two-dimensional grids over the front portion of an airfoil are used to demonstrate the effect. As the grid density is increased, the laminar region near the nose becomes larger. In the Spalart-Allmaras model this behavior is due to convergence to a laminar-behavior fixed point that occurs in practice when freestream turbulence is below some threshold. It is the result of a feature purposefully added to the original model in conjunction with a special trip function. This degenerate fixed point can also cause non-uniqueness regarding where transition initiates on a given grid. Consistent fully turbulent results can easily be achieved by either using a higher freestream turbulence level or by making a simple change to one of the model constants. Two-equation k-omega models, including the SST model, exhibit strong sensitivity to numerical resolution near the area where turbulence initiates. Thus, inconsistent apparent transition behavior with grid refinement in this case does not appear to stem from the presence of a degenerate fixed point. Rather, it is a fundamental property of the k-omega model itself, and is not easily remedied.

Contrasting dynamics of fragile and non-fragile polyalcohols through the glass, and dynamical, transitions: A comparison of neutron scattering and dielectric relaxation data for sorbitol and glycerol.

PubMed

Migliardo, F; Angell, C A; Magazù, S

2017-01-01

Glycerol and sorbitol are glass-forming hydrogen-bonded systems characterized by intriguing properties which make these systems very interesting also from the applications point of view. The goal of this work is to relate the hydrogen-bonded features, relaxation dynamics, glass transition properties and fragility of these systems, in particular to seek insight into their very different liquid fragilities. The comparison between glycerol and sorbitol is carried out by collecting the elastic incoherent neutron scattering (EINS) intensity as a function of temperature and of the instrumental energy resolution. Intensity data vs temperature and resolution are analyzed in terms of thermal restraint and Resolution Elastic Neutron Scattering (RENS) approaches. The number of OH groups, which are related to the connecting sites, is a significant parameter both in the glass transition and in the dynamical transition. On the other hand, the disordered nature of sorbitol is confirmed by the existence of different relaxation processes. From the applications point of view, glycerol and sorbitol have remarkable bioprotectant properties which make these systems useful in different technological and industrial fields. Furthermore, polyols are rich in glassforming liquid phenomenology and highly deserving of study in their own right. The comparison of EINS and calorimetric data on glycerol and sorbitol helps provide a connection between structural relaxation, dynamical transition, glass transition, and fragility. The evaluation of the inflection point in the elastic intensity behavior as a function of temperature and instrumental energy resolution provides a confirmation of the validity of the RENS approach. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo. Copyright © 2016. Published by Elsevier B.V.

Motor Decisions Are Not Black and White: Selecting Actions in the “Gray Zone”

PubMed Central

Comalli, D. M.; Persand, D.; Adolph, K. E.

2017-01-01

In many situations, multiple actions are possible to achieve a goal. How do people select a particular action among equally possible alternatives? In six experiments, we determined whether action selection is consistent and biased toward one decision by observing participants’ decisions to go over or under a horizontal bar set at varying heights. We assessed the height at which participants transitioned from going over to under the bar within a “gray zone”—the range of bar heights at which going over and under were both possible. In Experiment 1, participants’ transition points were consistently located near the upper boundary of the gray zone, indicating a bias to go over rather than under the bar. Moreover, transitional behaviors were clustered tightly into a small region, indicating that decisions were highly consistent. Subsequent experiments examined potential influences on action selection. In Experiment 2, participants wore ankle weights to increase the cost of going over the bar. In Experiment 3, they were tested on a padded surface that made crawling under the bar more comfortable. In Experiment 4, we introduced a secondary task that required participants to crawl immediately after navigating the bar. None of these manipulations altered participants’ decisions relative to Experiment 1. In Experiment 5, participants started in a crawling position, which led to significantly lower transition points. In Experiment 6, we tested 5- to 6-year-old children as in Experiment 1 to determine the effects of social pressure on action selection. Children displayed lower transition points, larger transition regions, and reduced ability to go over the bar compared to adults. Across experiments, results indicate that adults have a strong and robust bias for upright locomotion. PMID:28293691

Merging of the Dirac points in electronic artificial graphene

NASA Astrophysics Data System (ADS)

Feilhauer, J.; Apel, W.; Schweitzer, L.

2015-12-01

Theory predicts that graphene under uniaxial compressive strain in an armchair direction should undergo a topological phase transition from a semimetal into an insulator. Due to the change of the hopping integrals under compression, both Dirac points shift away from the corners of the Brillouin zone towards each other. For sufficiently large strain, the Dirac points merge and an energy gap appears. However, such a topological phase transition has not yet been observed in normal graphene (due to its large stiffness) neither in any other electronic system. We show numerically and analytically that such a merging of the Dirac points can be observed in electronic artificial graphene created from a two-dimensional electron gas by application of a triangular lattice of repulsive antidots. Here, the effect of strain is modeled by tuning the distance between the repulsive potentials along the armchair direction. Our results show that the merging of the Dirac points should be observable in a recent experiment with molecular graphene.

Avalanche of entanglement and correlations at quantum phase transitions.

PubMed

Krutitsky, Konstantin V; Osterloh, Andreas; Schützhold, Ralf

2017-06-16

We study the ground-state entanglement in the quantum Ising model with nearest neighbor ferromagnetic coupling J and find a sequential increase of entanglement depth d with growing J. This entanglement avalanche starts with two-point entanglement, as measured by the concurrence, and continues via the three-tangle and four-tangle, until finally, deep in the ferromagnetic phase for J = ∞, arriving at a pure L-partite (GHZ type) entanglement of all L spins. Comparison with the two, three, and four-point correlations reveals a similar sequence and shows strong ties to the above entanglement measures for small J. However, we also find a partial inversion of the hierarchy, where the four-point correlation exceeds the three- and two-point correlations, well before the critical point is reached. Qualitatively similar behavior is also found for the Bose-Hubbard model, suggesting that this is a general feature of a quantum phase transition. This should be taken into account in the approximations starting from a mean-field limit.

Optical signature of Weyl electronic structures in tantalum pnictides Ta P n (P n = P, As)

NASA Astrophysics Data System (ADS)

Kimura, Shin-ichi; Yokoyama, Hiroko; Watanabe, Hiroshi; Sichelschmidt, Jörg; Süß, Vicky; Schmidt, Marcus; Felser, Claudia

2017-08-01

To investigate the electronic structure of Weyl semimetals Ta P n (P n = P, As), optical conductivity [σ (ω )] spectra are measured over a wide range of photon energies and temperatures, and these measured values are compared with band calculations. Two significant structures can be observed: a bending structure at ℏ ω ˜85 meV in TaAs, and peaks at ℏ ω ˜ 50 meV (TaP) and ˜30 meV (TaAs). The bending structure can be explained by the interband transition between saddle points connecting a set of W2 Weyl points. The temperature dependence of the peak intensity can be fitted by assuming the interband transition between saddle points connecting a set of W1 Weyl points. Owing to the different temperature dependence of the Drude weight in both materials, it is found that the Weyl points of TaAs are located near the Fermi level, whereas those of TaP are further away.

Hairy black holes in cubic quasi-topological gravity

NASA Astrophysics Data System (ADS)

Dykaar, Hannah; Hennigar, Robie A.; Mann, Robert B.

2017-05-01

We construct a class of five dimensional black hole solutions to cubic quasi-topological gravity with conformal scalar hair and study their thermodynamics. We find these black holes provide the second example of black hole λ-lines: a line of second order (continuous) phase transitions, akin to the fluid/superfluid transition of 4He. Examples of isolated critical points are found for spherical black holes, marking the first in the literature to date. We also find various novel and interesting phase structures, including an isolated critical point occurring in conjunction with a double reentrant phase transition. The AdS vacua of the theory are studied, finding ghost-free configurations where the scalar field takes on a non-zero constant value, in notable contrast to the five dimensional Lovelock case.

Activity of a social dynamics model

NASA Astrophysics Data System (ADS)

Reia, Sandro M.; Neves, Ubiraci P. C.

2015-10-01

Axelrod's model was proposed to study interactions between agents and the formation of cultural domains. It presents a transition from a monocultural to a multicultural steady state which has been studied in the literature by evaluation of the relative size of the largest cluster. In this article, we propose new measurements based on the concept of activity per agent to study the Axelrod's model on the square lattice. We show that the variance of system activity can be used to indicate the critical points of the transition. Furthermore the frequency distribution of the system activity is able to show a coexistence of phases typical of a first order phase transition. Finally, we verify a power law dependence between cluster activity and cluster size for multicultural steady state configurations at the critical point.

The thermal properties of Martian surface materials at high lattitudes: Possible evidence for permafrost

NASA Technical Reports Server (NTRS)

Paige, D. A.; Kieffer, H. H.

1987-01-01

Evidence is presented from analysis of Viking thermal mapping results that suggests a transition to high thermal inertial material at a depth of approx. 12 cm at +75 deg latitude. This was interpreted as reflecting the transition from ice poor soil to hard frozen permafrost. It was pointed out that such a transition would be expected on the basis of theoretical models of hard frozen permafrost distribution. Although permafrost is not the only plausible martian surface material with high thermal inertia, polar thermal mapping may turn out to be a powerful tool for determining the distribution of permafrost deposits and understanding their behavior. At this point, the circumstantial case for permafrost deposits in the north pole region of Mars is very strong.

On the Critical Behaviour, Crossover Point and Complexity of the Exact Cover Problem

NASA Technical Reports Server (NTRS)

Morris, Robin D.; Smelyanskiy, Vadim N.; Shumow, Daniel; Koga, Dennis (Technical Monitor)

2003-01-01

Research into quantum algorithms for NP-complete problems has rekindled interest in the detailed study a broad class of combinatorial problems. A recent paper applied the quantum adiabatic evolution algorithm to the Exact Cover problem for 3-sets (EC3), and provided an empirical evidence that the algorithm was polynomial. In this paper we provide a detailed study of the characteristics of the exact cover problem. We present the annealing approximation applied to EC3, which gives an over-estimate of the phase transition point. We also identify empirically the phase transition point. We also study the complexity of two classical algorithms on this problem: Davis-Putnam and Simulated Annealing. For these algorithms, EC3 is significantly easier than 3-SAT.

Black holes as critical point of quantum phase transition.

PubMed

Dvali, Gia; Gomez, Cesar

We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

AN ENIGMATIC POINT-LIKE FEATURE WITHIN THE HD 169142 TRANSITIONAL DISK ,

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biller, Beth A.; Males, Jared; Morzinski, Katie

2014-09-01

We report the detection of a faint point-like feature possibly related to ongoing planet-formation in the disk of the transition disk star HD 169142. The point-like feature has a Δmag(L) ∼ 6.4, at a separation of ∼0.''11 and position angle ∼0°. Given its lack of an H or K{sub S} counterpart despite its relative brightness, this candidate cannot be explained by purely photospheric emission and must be a disk feature heated by an as yet unknown source. Its extremely red colors make it highly unlikely to be a background object, but future multi-wavelength follow up is necessary for confirmation and characterization ofmore » this feature.« less

Random growth lattice filling model of percolation: a crossover from continuous to discontinuous transition

NASA Astrophysics Data System (ADS)

Roy, Bappaditya; Santra, S. B.

2018-05-01

A random growth lattice filling model of percolation with a touch and stop growth rule is developed and studied numerically on a two dimensional square lattice. Nucleation centers are continuously added one at a time to the empty lattice sites and clusters are grown from these nucleation centers with a growth probability g. For a given g (), the system passes through a critical point during the growth process where the transition from a disconnected to a connected phase occurs. The model is found to exhibit second order continuous percolation transitions as ordinary percolation for whereas for it exhibits weak first order discontinuous percolation transitions. The continuous transitions are characterized by estimating the values of the critical exponents associated with the order parameter fluctuation and the fractal dimension of the spanning cluster over the whole range of g. The discontinuous transitions, however, are characterized by a compact spanning cluster, lattice size independent fluctuation of the order parameter per lattice, departure from power law scaling in the cluster size distribution and weak bimodal distribution of the order parameter. The nature of transitions are further confirmed by studying the Binder cumulant. Instead of a sharp tricritical point, a tricritical region is found to occur for 0.5  <  g  <  0.8 within which the values of the critical exponents change continuously until the crossover from continuous to discontinuous transition is completed.

78 FR 23843 - Special Local Regulations; Moss Point Rockin' the Riverfront Festival; Robertson Lake & O'Leary...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-23

...-AA08 Special Local Regulations; Moss Point Rockin' the Riverfront Festival; Robertson Lake & O'Leary... Festival high speed boat races. Entry into, transiting or anchoring in this area is prohibited to all... Rockin' the Riverfront Festival; Robertson Lake & O'Leary Lake; Moss Point, MS. (a) Location. The...

Point-point and point-line moving-window correlation spectroscopy and its applications

NASA Astrophysics Data System (ADS)

Zhou, Qun; Sun, Suqin; Zhan, Daqi; Yu, Zhiwu

2008-07-01

In this paper, we present a new extension of generalized two-dimensional (2D) correlation spectroscopy. Two new algorithms, namely point-point (P-P) correlation and point-line (P-L) correlation, have been introduced to do the moving-window 2D correlation (MW2D) analysis. The new method has been applied to a spectral model consisting of two different processes. The results indicate that P-P correlation spectroscopy can unveil the details and re-constitute the entire process, whilst the P-L can provide general feature of the concerned processes. Phase transition behavior of dimyristoylphosphotidylethanolamine (DMPE) has been studied using MW2D correlation spectroscopy. The newly proposed method verifies that the phase transition temperature is 56 °C, same as the result got from a differential scanning calorimeter. To illustrate the new method further, a lysine and lactose mixture has been studied under thermo perturbation. Using the P-P MW2D, the Maillard reaction of the mixture was clearly monitored, which has been very difficult using conventional display of FTIR spectra.

Preparation and properties of Ge4Se96 glass

NASA Astrophysics Data System (ADS)

Xu, Junfeng; Sun, Guozhen; Liu, Zhenting; Wang, Yaling; Jian, Zengyun

2018-03-01

The chalcogenide glass Ge4Se96 was prepared by melt-quenched method. The characteristic temperatures (the strain point, annealing point, glass transition point, yielding point and soften point) were determined by thermal analysis. The result shows that the glass transition point is 52 °C; the average thermal expansion coefficient is ΔL/L0 = (0.0557∗T-1.7576)/1000. The specific heat of Ge4Se96 glass was measured by stepwise method. The difference in specific heat between amorphous structure and undercooled liquid was determined as ΔCp = 0.1812-5.20 × 10-4T-4.92 × 10-7T2 JK-1 g-1. Based on the result of ΔCp, the Gibbs energy and the entropy curves were calculated, and the Kauzmann temperature was determined as Tk = 233.5 K, which is between that for pure Se glass (216 K) and that for Ge7.4Se92.6 glass (250 K). It indicates that for Ge-Se glass with low Ge content, the Kauzmann temperature increases with increasing the content of Ge.

Toward the renewables - A natural gas/solar energy transition strategy

NASA Technical Reports Server (NTRS)

Hanson, J. A.; Escher, W. J. D.

1979-01-01

The inevitability of an energy transition from today's non-renewable fossil base toward a renewable energy base is considered from the viewpoint of the need for a national transition strategy. Then, one such strategy is offered. Its technological building blocks are described in terms of both energy use and energy supply. The strategy itself is then sketched at four points in its implementation; (1) initiation, (2) early transition, (3) late transition, and (4) completion. The transition is assumed to evolve from a heavily natural gas-dependent energy economy. It then proceeds through its transition toward a balanced, hybrid energy system consisting of both centralized and dispersed energy supply technologies supplying hydrogen and electricity from solar energy. Related institutional, environmental and economic factors are examined briefly.

A generalized force-modified potential energy surface (G-FMPES) for mechanochemical simulations

DOE PAGES

Subramanian, Gopinath; Mathew, Nithin; Leiding, Jeffery A.

2015-10-05

We describe the modifications that a spatially varying external load produces on a Born-Oppenheimer potential energy surface (PES) by calculating static quantities of interest. The effects of the external loads are exemplified using electronic structure calculations (at the HF/6-31G** level) of two different molecules: ethane and hexahydro-1,3,5-trinitro-s-triazine (RDX). The calculated transition states and The Hessian matrices of stationary points show that spatially varying external loads shift the stationary points and modify the curvature of the PES, thereby affecting the harmonic transition rates by altering both the energy barrier as well as the prefactor. The harmonic spectra of both molecules aremore » blue-shifted with increasing compressive “pressure.” Some stationary points on the RDX-PES disappear under application of the external load, indicating the merging of an energy minimum with a saddle point.« less

Coexistence of tunable Weyl points and topological nodal lines in ternary transition-metal telluride TaIrT e4

NASA Astrophysics Data System (ADS)

Zhou, Xiaoqing; Liu, Qihang; Wu, QuanSheng; Nummy, Tom; Li, Haoxiang; Griffith, Justin; Parham, Stephen; Waugh, Justin; Emmanouilidou, Eve; Shen, Bing; Yazyev, Oleg V.; Ni, Ni; Dessau, Daniel

2018-06-01

We report a combined theoretical and experimental study on TaIrT e4 , a potential candidate for a minimal model of type-II Weyl semimetals. Unexpectedly, an intriguing node structure with 12 Weyl points and a pair of nodal lines protected by mirror symmetry was found by first-principles calculations. Some signatures of the complex electronic structure, such as topologically nontrivial band crossings and topologically trivial Fermi arcs, are cross-validated by angle-resolved photoemission spectroscopy. Through external strain, the number of Weyl points can be reduced to a theoretical minimum of four, and the appearance of the nodal lines can be switched between different mirror planes in momentum space. The coexistence of switchable Weyl points and nodal lines establishes transition-metal chalcogenides as a unique test ground for topological state characterization and engineering.

A probabilistic approach for channel initiation

Treesearch

Erkan Istanbulluoglu; David G. Tarboton; Robert T. Pack; Charles H. Luce

2002-01-01

The channel head represents an important transition point from hillslope to fluvial processes. There is a nonlinear threshold transition across the channel head with sediment transport much larger in channels than on hillslopes. Deterministic specific catchment area, a, thresholds for channel initiation, sometimes dependent on slope, S...

International Student-Athlete Adjustment Issues: Advising Recommendations for Effective Transitions

ERIC Educational Resources Information Center

Newell, Emily M.

2015-01-01

Through an extensive literature review, student--athlete college transition issues as well as concerns of international student-athletes are identified. Research on general student advising, developmental advising, and mentoring literature points to successful tactics for assisting domestic students, international students, and student-athletes…

Probing deconfinement in a chiral effective model with Polyakov loop at imaginary chemical potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morita, Kenji; Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502; Skokov, Vladimir

2011-10-01

The phase structure of the two-flavor Polyakov-loop extended Nambu-Jona-Lashinio model is explored at finite temperature and imaginary chemical potential with a particular emphasis on the confinement-deconfinement transition. We point out that the confined phase is characterized by a cos3{mu}{sub I}/T dependence of the chiral condensate on the imaginary chemical potential while in the deconfined phase this dependence is given by cos{mu}{sub I}/T and accompanied by a cusp structure induced by the Z(3) transition. We demonstrate that the phase structure of the model strongly depends on the choice of the Polyakov loop potential U. Furthermore, we find that by changing themore » four fermion coupling constant G{sub s}, the location of the critical end point of the deconfinement transition can be moved into the real chemical potential region. We propose a new parameter characterizing the confinement-deconfinement transition.« less

Anomalous phase behavior of first-order fluid-liquid phase transition in phosphorus

NASA Astrophysics Data System (ADS)

Zhao, G.; Wang, H.; Hu, D. M.; Ding, M. C.; Zhao, X. G.; Yan, J. L.

2017-11-01

Although the existence of liquid-liquid phase transition has become more and more convincing, whether it will terminate at a critical point and what is the order parameter are still open. To explore these questions, we revisit the fluid-liquid phase transition (FLPT) in phosphorus (P) and study its phase behavior by performing extensive first-principles molecular dynamics simulations. The FLPT observed in experiments is well reproduced, and a fluid-liquid critical point (FLCP) at T = 3000 ˜ 3500 K, P = 1.5-2.0 Kbar is found. With decreasing temperature from the FLCP along the transition line, the density difference (Δρ) between two coexisting phases first increases from zero and then anomalously decreases; however, the entropy difference (ΔS) continuously increases from zero. These features suggest that an order parameter containing contributions from both the density and the entropy is needed to describe the FLPT in P, and at least at low temperatures, the entropy, instead of the density, governs the FLPT.

Chiral phase transition at finite chemical potential in 2 +1 -flavor soft-wall anti-de Sitter space QCD

NASA Astrophysics Data System (ADS)

Bartz, Sean P.; Jacobson, Theodore

2018-04-01

The phase transition from hadronic matter to chirally symmetric quark-gluon plasma is expected to be a rapid crossover at zero quark chemical potential (μ ), becoming first order at some finite value of μ , indicating the presence of a critical point. Using a three-flavor soft-wall model of anti-de Sitter/QCD, we investigate the effect of varying the light and strange quark masses on the order of the chiral phase transition. At zero quark chemical potential, we reproduce the Columbia Plot, which summarizes the results of lattice QCD and other holographic models. We then extend this holographic model to examine the effects of finite quark chemical potential. We find that the the chemical potential does not affect the critical line that separates first-order from rapid crossover transitions. This excludes the possibility of a critical point in this model, suggesting that a different setup is necessary to reproduce all the features of the QCD phase diagram.

Percolation of networks with directed dependency links

NASA Astrophysics Data System (ADS)

Niu, Dunbiao; Yuan, Xin; Du, Minhui; Stanley, H. Eugene; Hu, Yanqing

2016-04-01

The self-consistent probabilistic approach has proven itself powerful in studying the percolation behavior of interdependent or multiplex networks without tracking the percolation process through each cascading step. In order to understand how directed dependency links impact criticality, we employ this approach to study the percolation properties of networks with both undirected connectivity links and directed dependency links. We find that when a random network with a given degree distribution undergoes a second-order phase transition, the critical point and the unstable regime surrounding the second-order phase transition regime are determined by the proportion of nodes that do not depend on any other nodes. Moreover, we also find that the triple point and the boundary between first- and second-order transitions are determined by the proportion of nodes that depend on no more than one node. This implies that it is maybe general for multiplex network systems, some important properties of phase transitions can be determined only by a few parameters. We illustrate our findings using Erdős-Rényi networks.

Universality of phase transition dynamics: topological defects from symmetry breaking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zurek, Wojciech H.; Del Campo, Adolfo

In the course of a non-equilibrium continuous phase transition, the dynamics ceases to be adiabatic in the vicinity of the critical point as a result of the critical slowing down (the divergence of the relaxation time in the neighborhood of the critical point). This enforces a local choice of the broken symmetry and can lead to the formation of topological defects. The Kibble-Zurek mechanism (KZM) was developed to describe the associated nonequilibrium dynamics and to estimate the density of defects as a function of the quench rate through the transition. During recent years, several new experiments investigating formation of defectsmore » in phase transitions induced by a quench both in classical and quantum mechanical systems were carried out. At the same time, some established results were called into question. We review and analyze the Kibble-Zurek mechanism focusing in particular on this surge of activity, and suggest possible directions for further progress.« less

33 CFR 162.40 - Inland waterway from Delaware River to Chesapeake Bay, Del. and Md. (Chesapeake and Delaware Canal).

Code of Federal Regulations, 2010 CFR

2010-07-01

...., between Reedy Point, Delaware River, and Old Town Point Wharf, Elk River. (b) Speed. No vessel in the..., are required to travel at all times at a safe speed throughout the canal and its approaches so as to... Point and Welch Point. (f) Sailboats. Transiting the canal by vessels under sail is not permitted...

Optimal Number and Allocation of Data Collection Points for Linear Spline Growth Curve Modeling: A Search for Efficient Designs

ERIC Educational Resources Information Center

Wu, Wei; Jia, Fan; Kinai, Richard; Little, Todd D.

2017-01-01

Spline growth modelling is a popular tool to model change processes with distinct phases and change points in longitudinal studies. Focusing on linear spline growth models with two phases and a fixed change point (the transition point from one phase to the other), we detail how to find optimal data collection designs that maximize the efficiency…

A Demonstration of the Continuous Phase (Second-Order) Transition of a Binary Liquid System in the Region around Its Critical Point

ERIC Educational Resources Information Center

Johnson, Michael R.

2006-01-01

In most general chemistry and introductory physical chemistry classes, critical point is defined as that temperature-pressure point on a phase diagram where the liquid-gas interface disappears, a phenomenon that generally occurs at relatively high temperatures or high pressures. Two examples are: water, with a critical point at 647 K (critical…

Co-C and Pd-C Fixed Points for the Evaluation of Facilities and Scales Realization at INRIM and NMC

NASA Astrophysics Data System (ADS)

Battuello, M.; Wang, L.; Girard, F.; Ang, S. H.

2014-04-01

Two hybrid cells for realizing the Co-C and Pd-C fixed points and constructed at Istituto Nazionale di Ricerca Metrologica (INRIM) were used for an evaluation of facilities and procedures adopted by INRIM and National Metrology Institute of Singapore (NMC) for the realization of the solid-liquid phase transitions of high-temperature fixed points and for determining their transition temperatures. Four different furnaces were used for the investigations, i.e., two single-zone furnaces, one of them of the direct-heating type, and two identical three-zone furnaces. The transition temperatures were measured at both institutes by adopting different procedures for realizing the radiation scales, i.e., at INRIM a scheme based on the extrapolation of fixed-point interpolated scales and an International Temperature Scale of 1990 (ITS-90) approach at NMC. The point of inflection (POI) of the melting curves was determined and assumed as a practical representation of the melting temperature. Different methods for deriving the POI were used, and differences as large as some hundredths of a kelvin were found with the different approaches. The POIs of the different melting curves were analyzed with respect to the different possible operative conditions with the aim of deriving reproducibility figures to improve the estimated uncertainty. As regard to the institutes inter-comparison, differences of 0.13 K and 0.29 K were found between INRIM and NMC determinations at the Co-C and Pd-C points, respectively. Such differences are compatible with the combined standard uncertainties of the comparison, which are estimated to be 0.33 K and 0.36 K at the Co-C and Pd-C points, respectively.

Sampling saddle points on a free energy surface

NASA Astrophysics Data System (ADS)

Samanta, Amit; Chen, Ming; Yu, Tang-Qing; Tuckerman, Mark; E, Weinan

2014-04-01

Many problems in biology, chemistry, and materials science require knowledge of saddle points on free energy surfaces. These saddle points act as transition states and are the bottlenecks for transitions of the system between different metastable states. For simple systems in which the free energy depends on a few variables, the free energy surface can be precomputed, and saddle points can then be found using existing techniques. For complex systems, where the free energy depends on many degrees of freedom, this is not feasible. In this paper, we develop an algorithm for finding the saddle points on a high-dimensional free energy surface "on-the-fly" without requiring a priori knowledge the free energy function itself. This is done by using the general strategy of the heterogeneous multi-scale method by applying a macro-scale solver, here the gentlest ascent dynamics algorithm, with the needed force and Hessian values computed on-the-fly using a micro-scale model such as molecular dynamics. The algorithm is capable of dealing with problems involving many coarse-grained variables. The utility of the algorithm is illustrated by studying the saddle points associated with (a) the isomerization transition of the alanine dipeptide using two coarse-grained variables, specifically the Ramachandran dihedral angles, and (b) the beta-hairpin structure of the alanine decamer using 20 coarse-grained variables, specifically the full set of Ramachandran angle pairs associated with each residue. For the alanine decamer, we obtain a detailed network showing the connectivity of the minima obtained and the saddle-point structures that connect them, which provides a way to visualize the gross features of the high-dimensional surface.

Electromagnetically induced transparency and Autler-Townes splitting in superconducting flux quantum circuits

NASA Astrophysics Data System (ADS)

Sun, Hui-Chen; Liu, Yu-xi; Ian, Hou; You, J. Q.; Il'ichev, E.; Nori, Franco

2014-06-01

We study the microwave absorption of a driven three-level quantum system, which is realized by a superconducting flux quantum circuit (SFQC), with a magnetic driving field applied to the two upper levels. The interaction between the three-level system and its environment is studied within the Born-Markov approximation, and we take into account the effects of the driving field on the damping rates of the three-level system. We study the linear response of the driven three-level SFQC to a weak probe field. The linear magnetic susceptibility of the SFQC can be changed by both the driving field and the bias magnetic flux. When the bias magnetic flux is at the optimal point, the transition from the ground state to the second-excited state is forbidden and the three-level SFQC has a ladder-type transition. Thus, the SFQC responds to the probe field like natural atoms with ladder-type transitions. However, when the bias magnetic flux deviates from the optimal point, the three-level SFQC has a cyclic transition, thus it responds to the probe field like a combination of natural atoms with ladder-type transitions and natural atoms with Λ-type transitions. In particular, we provide detailed discussions on the conditions for realizing electromagnetically induced transparency and Autler-Townes splitting in three-level SFQCs.

Dynamics of Ecosystem Services during Forest Transitions in Reventazón, Costa Rica.

PubMed

Vallet, Améline; Locatelli, Bruno; Levrel, Harold; Brenes Pérez, Christian; Imbach, Pablo; Estrada Carmona, Natalia; Manlay, Raphaël; Oszwald, Johan

2016-01-01

The forest transition framework describes the temporal changes of forest areas with economic development. A first phase of forest contraction is followed by a second phase of expansion once a turning point is reached. This framework does not differentiate forest types or ecosystem services, and describes forests regardless of their contribution to human well-being. For several decades, deforestation in many tropical regions has degraded ecosystem services, such as watershed regulation, while increasing provisioning services from agriculture, for example, food. Forest transitions and expansion have been observed in some countries, but their consequences for ecosystem services are often unclear. We analyzed the implications of forest cover change on ecosystem services in Costa Rica, where a forest transition has been suggested. A review of literature and secondary data on forest and ecosystem services in Costa Rica indicated that forest transition might have led to an ecosystem services transition. We modeled and mapped the changes of selected ecosystem services in the upper part of the Reventazón watershed and analyzed how supply changed over time in order to identify possible transitions in ecosystem services. The modeled changes of ecosystem services is similar to the second phase of a forest transition but no turning point was identified, probably because of the limited temporal scope of the analysis. Trends of provisioning and regulating services and their tradeoffs were opposite in different spatial subunits of our study area, which highlights the importance of scale in the analysis of ecosystem services and forest transitions. The ecosystem services transition framework proposed in this study is useful for analyzing the temporal changes of ecosystem services and linking socio-economic drivers to ecosystem services demand at different scales.

Dynamics of Ecosystem Services during Forest Transitions in Reventazón, Costa Rica

PubMed Central

Vallet, Améline; Locatelli, Bruno; Levrel, Harold; Brenes Pérez, Christian; Imbach, Pablo; Estrada Carmona, Natalia; Manlay, Raphaël; Oszwald, Johan

2016-01-01

The forest transition framework describes the temporal changes of forest areas with economic development. A first phase of forest contraction is followed by a second phase of expansion once a turning point is reached. This framework does not differentiate forest types or ecosystem services, and describes forests regardless of their contribution to human well-being. For several decades, deforestation in many tropical regions has degraded ecosystem services, such as watershed regulation, while increasing provisioning services from agriculture, for example, food. Forest transitions and expansion have been observed in some countries, but their consequences for ecosystem services are often unclear. We analyzed the implications of forest cover change on ecosystem services in Costa Rica, where a forest transition has been suggested. A review of literature and secondary data on forest and ecosystem services in Costa Rica indicated that forest transition might have led to an ecosystem services transition. We modeled and mapped the changes of selected ecosystem services in the upper part of the Reventazón watershed and analyzed how supply changed over time in order to identify possible transitions in ecosystem services. The modeled changes of ecosystem services is similar to the second phase of a forest transition but no turning point was identified, probably because of the limited temporal scope of the analysis. Trends of provisioning and regulating services and their tradeoffs were opposite in different spatial subunits of our study area, which highlights the importance of scale in the analysis of ecosystem services and forest transitions. The ecosystem services transition framework proposed in this study is useful for analyzing the temporal changes of ecosystem services and linking socio-economic drivers to ecosystem services demand at different scales. PMID:27390869

The Work Instability Scale for rheumatoid arthritis predicts arthritis-related work transitions within 12 months.

PubMed

Tang, Kenneth; Beaton, Dorcas E; Gignac, Monique A M; Lacaille, Diane; Zhang, Wei; Bombardier, Claire

2010-11-01

Among people with arthritis, the need for work transitions may signal a risk for more adverse work outcomes in the future, such as permanent work loss. Our aim was to evaluate the ability of the Work Instability Scale for Rheumatoid Arthritis (RA-WIS) to predict arthritis-related work transitions within a 12-month period. Workers with osteoarthritis or rheumatoid arthritis (n = 250) from 3 clinical sites participated in self-administered surveys that assessed the impact of health on employment at multiple time points over 12 months. Multivariable logistic regressions were conducted to assess the ability of the RA-WIS (range 0-23, where 23 = highest work instability) to predict 4 types of work transition: reductions in work hours, disability leaves of absence, changes in job/occupation, or temporary unemployment, assembled as a composite outcome. Covariates assessed include age, sex, education, marital status, income, pain intensity, disease duration, and the Health Assessment Questionnaire. Areas under the receiver operating characteristic curves (AUROCCs) were also assessed to further examine the predictive ability of the RA-WIS and to determine optimal cut points for predicting specific work transitions. After 12 months, 21.7% (n = 50 of 230) of the participants had indicated at least one arthritis-related work transition. Higher baseline RA-WIS was predictive of such an outcome (relative risk [RR] 1.05 [95% confidence interval (95% CI) 1.00-1.11]), particularly at >17 (RR 2.30 [95% CI 1.11-4.77]). The RA-WIS cut point of >13 was found to be most accurate for prediction (AUROCC 0.68 [95% CI 0.58-0.78]). The RA-WIS demonstrated the ability to predict arthritis-related work transitions within a short timeframe, and could be a promising measurement candidate for risk prognostication where work disability outcomes are of concern. Copyright © 2010 by the American College of Rheumatology.

Phase transitions in high magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arko, A.J.; Beers, C.J.; van Deursen, A.P.J.

1982-08-01

The purpose of this paper is to summarize some of the research activities recently performed at the Laboratorium voor Hoge Magneetvelden at the University of Nijmegen. The scope here and unifying aspect is magnetically induced phase transitions. Here we summarize transitions in the settling velocity of paramagnetic aggregates, suppression of spin fluctuations in UAl/sub 2/, the phase diagram of a ferroelectric chiral smectic liquid crystal near the Lifshitz point and the transition from 3D to 2D conduction in a GaAs FET. In no way does this represent a complete review of transitions, but rather a summary of phase transitions observedmore » at the magnet laboratory during the past year. 6 figures.« less

Broadband optical properties of graphene and HOPG investigated by spectroscopic Mueller matrix ellipsometry

NASA Astrophysics Data System (ADS)

Song, Baokun; Gu, Honggang; Zhu, Simin; Jiang, Hao; Chen, Xiuguo; Zhang, Chuanwei; Liu, Shiyuan

2018-05-01

Optical properties of mono-graphene fabricated by chemical vapor deposition (CVD) and highly oriented pyrolytic graphite (HOPG) are comparatively studied by Mueller matrix ellipsometry (MME) over an ultra-wide energy range of 0.73-6.42 eV. A multilayer stacking model is constructed to describe the CVD mono-graphene, in which the roughness of the glass substrate and the water adsorption on the graphene are considered. We introduce a uniaxial anisotropic dielectric model to parameterize the optical constants of both the graphene and the HOPG. With the established models, broadband optical constants of the graphene and the HOPG are determined from the Mueller matrix spectra based on a point-by-point method and a non-linear regression method, respectively. Two significant absorption peaks at 4.75 eV and 6.31 eV are observed in the extinction coefficient spectra of the mono-graphene, which can be attributed to the von-Hove singularity (i.e., the π-to-π∗ exciton transition) near the M point and the σ-to-σ∗ exciton transition near the Γ point of the Brillouin zone, respectively. Comparatively, only a major absorption peak at 4.96 eV appears in the ordinary extinction coefficient spectra of the HOPG, which is mainly formed by the π-to-π∗ interband transition.

Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mauguière, Frédéric A. L., E-mail: frederic.mauguiere@bristol.ac.uk; Collins, Peter, E-mail: peter.collins@bristol.ac.uk; Wiggins, Stephen, E-mail: stephen.wiggins@mac.com

We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariantmore » manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.« less

Continuity and Discontinuity in Education: Example of Transition from Preschool to School

ERIC Educational Resources Information Center

Babic, Nada

2017-01-01

This article reconsiders multiple perspectives about continuity and discontinuity of early childhood education. Theoretical starting points, childhood policies and research of continuity and discontinuity exemplified through transition to school, are promising in rethinking and creating productive practices of childhood in different sociocultural…

Transitions and Turning Points: Navigating the Passage from Childhood through Adolescence.

ERIC Educational Resources Information Center

Graber, Julia A.; Brooks-Gunn, Jeanne

1996-01-01

Comments on this special theme issue examining the roles of socialization, biology, and culture as they affect adaptive and maladaptive developmental outcomes. Presents models for predicting and understanding behavioral and affective change at transitions occurring especially from middle childhood through adolescence. Provides examples…

Family Instability and Child Well-Being

ERIC Educational Resources Information Center

Fomby, Paula; Cherlin, Andrew J.

2007-01-01

Children who experience multiple transitions in family structure may face worse developmental outcomes than children raised in stable, two-parent families, and perhaps even worse than children raised in stable, single-parent families--a point denoted in much prior research. Multiple transitions and negative child outcomes, however, may be…

Nematic order on the surface of a three-dimensional topological insulator

NASA Astrophysics Data System (ADS)

Lundgren, Rex; Yerzhakov, Hennadii; Maciejko, Joseph

2017-12-01

We study the spontaneous breaking of rotational symmetry in the helical surface state of three-dimensional topological insulators due to strong electron-electron interactions, focusing on time-reversal invariant nematic order. Owing to the strongly spin-orbit coupled nature of the surface state, the nematic order parameter is linear in the electron momentum and necessarily involves the electron spin, in contrast with spin-degenerate nematic Fermi liquids. For a chemical potential at the Dirac point (zero doping), we find a first-order phase transition at zero temperature between isotropic and nematic Dirac semimetals. This extends to a thermal phase transition that changes from first to second order at a finite-temperature tricritical point. At finite doping, we find a transition between isotropic and nematic helical Fermi liquids that is second order even at zero temperature. Focusing on finite doping, we discuss various observable consequences of nematic order, such as anisotropies in transport and the spin susceptibility, the partial breakdown of spin-momentum locking, collective modes and induced spin fluctuations, and non-Fermi-liquid behavior at the quantum critical point and in the nematic phase.

Stability analysis of type 2 diabetes mellitus prognosis model with obesity as a trigger factor and metabolic syndrome as a risk factor

NASA Astrophysics Data System (ADS)

Jaya, A. I.; Lestari, A. D.; Ratianingsih, R.; Puspitasari, J. W.

2018-03-01

Obesity is found in 90% of the world's patients with a type 2 diabetes mellitus (DM) diagnosis. If it is not being treatment, the disease advances to a metabolic syndrome related to some atherosclerotic cardiovascular diseases. In this study, a mathematical model was constructed that represent the prognosis of type 2 DM. The prognosis is started from the transition of vulnerable people to overweight and obese. The advanced prognosis makes the type 2 DM sufferer become a metabolic syndrome. The model has no disease-free critical point, while the implicit endemic critical point is guaranteed for some requirements. The analysis of the critical point stability, by Jacobian matrix and Routh Hurwitz criteria, requires a parameter interval that identified from the characteristic polynomial. The requirements show that we have to pay attention to the transition rate of overweight to obese, more over the transition rate of obese to type 2 DM. The simulations show that the unstable condition of type 2 DM is easier to achieve because of the tightness of the parameter stability interval.

Shear melting and high temperature embrittlement: theory and application to machining titanium.

PubMed

Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

2015-04-24

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Quench in the 1D Bose-Hubbard model: Topological defects and excitations from the Kosterlitz-Thouless phase transition dynamics

PubMed Central

Dziarmaga, Jacek; Zurek, Wojciech H.

2014-01-01

Kibble-Zurek mechanism (KZM) uses critical scaling to predict density of topological defects and other excitations created in second order phase transitions. We point out that simply inserting asymptotic critical exponents deduced from the immediate vicinity of the critical point to obtain predictions can lead to results that are inconsistent with a more careful KZM analysis based on causality – on the comparison of the relaxation time of the order parameter with the “time distance” from the critical point. As a result, scaling of quench-generated excitations with quench rates can exhibit behavior that is locally (i.e., in the neighborhood of any given quench rate) well approximated by the power law, but with exponents that depend on that rate, and that are quite different from the naive prediction based on the critical exponents relevant for asymptotically long quench times. Kosterlitz-Thouless scaling (that governs e.g. Mott insulator to superfluid transition in the Bose-Hubbard model in one dimension) is investigated as an example of this phenomenon. PMID:25091996

Identifying the critical point of the weakly first-order itinerant magnet DyCo2 with complementary magnetization and calorimetric measurements

NASA Astrophysics Data System (ADS)

Morrison, K.; Dupas, A.; Mudryk, Y.; Pecharsky, V. K.; Gschneidner, K. A.; Caplin, A. D.; Cohen, L. F.

2013-04-01

We examine the character of the itinerant magnetic transition of DyCo2 by different calorimetric methods, thereby separating the heat capacity and latent heat contributions to the entropy—allowing direct comparison to other itinerant electron metamagnetic systems. The heat capacity exhibits a large λ-like peak at the ferrimagnetic ordering phase transition, a signature that is remarkably similar to La(Fe,Si)13, where it is attributed to giant spin fluctuations. Using calorimetric measurements, we also determine the point at which the phase transition ceases to be first order: the critical magnetic field, μ0Hcrit = 0.4 ± 0.1 T and temperature Tcrit = 138.5 ± 0.5 K, and we compare these values to those obtained from analysis of magnetization by application of the Shimizu inequality for itinerant electron metamagnetism. Good agreement is found between these independent measurements, thus establishing the phase diagram and critical point with some confidence. In addition, we find that the often-used Banerjee criterion may not be suitable for determination of first order behavior in itinerant magnet systems.

OPEN PROBLEM: Turbulence transition in pipe flow: some open questions

NASA Astrophysics Data System (ADS)

Eckhardt, Bruno

2008-01-01

The transition to turbulence in pipe flow is a longstanding problem in fluid dynamics. In contrast to many other transitions it is not connected with linear instabilities of the laminar profile and hence follows a different route. Experimental and numerical studies within the last few years have revealed many unexpected connections to the nonlinear dynamics of strange saddles and have considerably improved our understanding of this transition. The text summarizes some of these insights and points to some outstanding problems in areas where valuable contributions from nonlinear dynamics can be expected.

Order of wetting transitions in electrolyte solutions.

PubMed

Ibagon, Ingrid; Bier, Markus; Dietrich, S

2014-05-07

For wetting films in dilute electrolyte solutions close to charged walls we present analytic expressions for their effective interface potentials. The analysis of these expressions renders the conditions under which corresponding wetting transitions can be first- or second-order. Within mean field theory we consider two models, one with short- and one with long-ranged solvent-solvent and solvent-wall interactions. The analytic results reveal in a transparent way that wetting transitions in electrolyte solutions, which occur far away from their critical point (i.e., the bulk correlation length is less than half of the Debye length) are always first-order if the solvent-solvent and solvent-wall interactions are short-ranged. In contrast, wetting transitions close to the bulk critical point of the solvent (i.e., the bulk correlation length is larger than the Debye length) exhibit the same wetting behavior as the pure, i.e., salt-free, solvent. If the salt-free solvent is governed by long-ranged solvent-solvent as well as long-ranged solvent-wall interactions and exhibits critical wetting, adding salt can cause the occurrence of an ion-induced first-order thin-thick transition which precedes the subsequent continuous wetting as for the salt-free solvent.

Self-assembly in Dipolar Fluids

NASA Astrophysics Data System (ADS)

Ronti, Michela; Kantorovich, Sofia

We are studying low temperature structural transitions in dipolar hard spheres (DHS), combining grand-canonical Monte Carlo simulations and direct analytical theoretical calculations. DHS is characterized by long-range anisotropic interactions: it consists of a point dipole at the center of a hard sphere. We are interested in low temperature and low density phase behaviour of DHS systems. From a theoretical point of view the process of self-assembly is not responsible for a phase transition; this belief was completely reverted by theoretical studies showing that the process of self-assembly is alone capable to induce phase transition. On the other hand in the last years it was proved that no sign of critical behaviour is observed, implementing efficient and tailored Monte Carlo algorithms. Moreover a theoretical approach based on Density Functional Theory was developed: a series of structural transitions were discovered providing evidence of a hierarchy in the structures on cooling. We are performing free-energy calculations in order to draw the phase diagram of DHS model. Comparing the numerical results with the theoretical ones shed light on the scenario of temperature induced structural transitions in magnetic nanocolloids. Etn-COLLDENSE (H2020-MCSA-ITN-2014, Grant No. 642774).

Holographic entropy and real-time dynamics of quarkonium dissociation in non-Abelian plasma

DOE PAGES

Iatrakis, Ioannis; Kharzeev, Dmitri E.

2016-04-26

The peak of the heavy quark pair entropy at the deconfinement transition, observed in lattice QCD, suggests that the transition is effectively driven by the increase of the entropy of bound states. The growth of the entropy with the interquark distance leads to the emergent entropic force that induces dissociation of quarkonium states. Since the quark-gluon plasma around the transition point is a strongly coupled system, we use the gauge-gravity duality to study the entropy of heavy quarkonium and the real-time dynamics of its dissociation. In particular, we employ the improved holographic QCD model as a dual description of largemore » N c Yang-Mills theory. Studying the dynamics of the fundamental string between the quarks placed on the boundary, we find that the entropy peaks at the transition point. We also study the real-time dynamics of the system by considering the holographic string falling in the black hole horizon where it equilibrates. As a result, in the vicinity of the deconfinement transition, the dissociation time is found to be less than a fermi, suggesting that the entropic destruction is the dominant dissociation mechanism in this temperature region.« less

Bootstrap percolation on spatial networks

NASA Astrophysics Data System (ADS)

Gao, Jian; Zhou, Tao; Hu, Yanqing

2015-10-01

Bootstrap percolation is a general representation of some networked activation process, which has found applications in explaining many important social phenomena, such as the propagation of information. Inspired by some recent findings on spatial structure of online social networks, here we study bootstrap percolation on undirected spatial networks, with the probability density function of long-range links’ lengths being a power law with tunable exponent. Setting the size of the giant active component as the order parameter, we find a parameter-dependent critical value for the power-law exponent, above which there is a double phase transition, mixed of a second-order phase transition and a hybrid phase transition with two varying critical points, otherwise there is only a second-order phase transition. We further find a parameter-independent critical value around -1, about which the two critical points for the double phase transition are almost constant. To our surprise, this critical value -1 is just equal or very close to the values of many real online social networks, including LiveJournal, HP Labs email network, Belgian mobile phone network, etc. This work helps us in better understanding the self-organization of spatial structure of online social networks, in terms of the effective function for information spreading.

Point-Defect Nature of the Ultraviolet Absorption Band in AlN

NASA Astrophysics Data System (ADS)

Alden, D.; Harris, J. S.; Bryan, Z.; Baker, J. N.; Reddy, P.; Mita, S.; Callsen, G.; Hoffmann, A.; Irving, D. L.; Collazo, R.; Sitar, Z.

2018-05-01

We present an approach where point defects and defect complexes are identified using power-dependent photoluminescence excitation spectroscopy, impurity data from SIMS, and density-functional-theory (DFT)-based calculations accounting for the total charge balance in the crystal. Employing the capabilities of such an experimental computational approach, in this work, the ultraviolet-C absorption band at 4.7 eV, as well as the 2.7- and 3.9-eV luminescence bands in AlN single crystals grown via physical vapor transport (PVT) are studied in detail. Photoluminescence excitation spectroscopy measurements demonstrate the relationship between the defect luminescent bands centered at 3.9 and 2.7 eV to the commonly observed absorption band centered at 4.7 eV. Accordingly, the thermodynamic transition energy for the absorption band at 4.7 eV and the luminescence band at 3.9 eV is estimated at 4.2 eV, in agreement with the thermodynamic transition energy for the CN- point defect. Finally, the 2.7-eV PL band is the result of a donor-acceptor pair transition between the VN and CN point defects since nitrogen vacancies are predicted to be present in the crystal in concentrations similar to carbon-employing charge-balance-constrained DFT calculations. Power-dependent photoluminescence measurements reveal the presence of the deep donor state with a thermodynamic transition energy of 5.0 eV, which we hypothesize to be nitrogen vacancies in agreement with predictions based on theory. The charge state, concentration, and type of impurities in the crystal are calculated considering a fixed amount of impurities and using a DFT-based defect solver, which considers their respective formation energies and the total charge balance in the crystal. The presented results show that nitrogen vacancies are the most likely candidate for the deep donor state involved in the donor-acceptor pair transition with peak emission at 2.7 eV for the conditions relevant to PVT growth.

The effect of doping on global lattice properties of magnetite Fe{sub 3-x}Me{sub x}O{sub 4} (Me=Zn, Ti and Al)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kakol, Z.; Owoc, D.; Przewoznik, J.

2012-08-15

X-ray powder diffraction was measured in Fe{sub 3-x}Me{sub x}O{sub 4} (Me=Zn, Ti, Al; x<0.065), in T range 70-300 K to see the effect of different doping on global lattice properties. The experimental results have shown that some lattice properties (e.g., the cell volume) are dopand specific. This can be attributed to the difference in preferential sites occupation by dopants. As confirmed by EXAFS, Zn enters tetrahedral, while Ti octahedral lattice sites, differently affecting crucial octahedral iron positions in the spinel lattice. However, despite this fact, it was found that T dependence of both monoclinic angle and lattice parameters is universalmore » for studied samples above and below the Verwey transition temperature T{sub V}. So, not the iron atoms in octahedral positions individually, but interactions between them are responsible for the Verwey transition character change with doping. - Graphical abstract: A low temperature magnetite cell volume vs. dopants content. Apparently, Zn, Ti and Al atoms have different effect on the global lattice properties at individual temperatures. However, the Verwey transition reacts to dopants in a similar manner, despite the different way the octahedral iron positions are affected. Highlights: Black-Right-Pointing-Pointer We measure powder diffraction and EXAFS on Fe{sub 3-x}Me{sub x}O{sub 4}, Me=Zn, Ti, Al (x<0.065), in T range 70-300 K. Black-Right-Pointing-Pointer XRD: atom-type independent changes of lattice parameters with T. Black-Right-Pointing-Pointer EXAFS: Zn replaces Fe on tetrahedral positions, Ti on octahedral positions. Black-Right-Pointing-Pointer Thus, some secondary interactions between ordering orbitals, not the primary one driving the Verwey transition, control the transition order.« less

On the reversibility of the Meissner effect and the angular momentum puzzle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirsch, J.E., E-mail: jhirsch@ucsd.edu

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay ofmore » eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes. - Highlights: • The normal-superconductor phase transition is reversible. • Within the conventional theory, Foucault currents give rise to irreversibility. • To suppress Foucault currents, charge has to flow in direction perpendicular to the phase boundary. • The charge carriers have to be holes. • This solves also the angular momentum puzzle associated with the Meissner effect.« less

Port Needs Study (Vessel Traffic Services Benefits). Volume 2: Appendices, Part 1

DTIC Science & Technology

1991-08-01

34 (Reference 1) and with its companion , Point Arguello, has been the graveyard of many ships. The Point Conception area has been described as a transition...North entrance to the Inner Harbor Navigation Canal, and that portion of the ICW Rigolets-New Orleans Cut west of a point one mile east of Chef

Proceedings of RIKEN BNL Resarch Center Workshop: Fluctuations, Correlations and RHIC Low Energy Runs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karsch, F.; Kojo, T.; Mukherjee, S.

Most of our visible universe is made up of hadronic matter. Quantum Chromodynamics (QCD) is the theory of strong interaction that describes the hadronic matter. However, QCD predicts that at high enough temperatures and/or densities ordinary hadronic matter ceases to exist and a new form of matter is created, the so-called Quark Gluon Plasma (QGP). Non-perturbative lattice QCD simulations shows that for high temperature and small densities the transition from the hadronic to the QCD matter is not an actual phase transition, rather it takes place via a rapid crossover. On the other hand, it is generally believed that atmore » zero temperature and high densities such a transition is an actual first order phase transition. Thus, in the temperature-density phase diagram of QCD, the first order phase transition line emanating from the zero temperature high density region ends at some higher temperature where the transition becomes a crossover. The point at which the first order transition line turns into a crossover is a second order phase transition point belonging to three dimensional Ising universality class. This point is known as the QCD Critical End Point (CEP). For the last couple of years the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been performing experiments at lower energies in search of the elusive QCD CEP. In general critical behaviors are manifested through appearance of long range correlations and increasing fluctuations associated with the presence of mass-less modes in the vicinity of a second order phase transition. Experimental signatures of the CEP are likely to be found in observables related to fluctuations and correlations. Thus, one of the major focuses of the RHIC low energy scan program is to measure various experimental observables connected to fluctuations and correlations. On the other hand, with the start of the RHIC low energy scan program, a flurry of activities are taking place to provide solid theoretical background for the search of the CEP using observables related to fluctuations and correlations. While new data are pouring in from the RHIC low energy scan program, many recent advances have also been made in the phenomenological and lattice gauge theory sides in order to have a better theoretical understanding of the wealth of new data. This workshop tried to create a synergy between the experimental, phenomenological and lattice QCD aspects of the fluctuation and correlation related studies of the RHIC low energy scan program. The workshop brought together all the leading experts from related fields under the same forum to share new ideas among themselves in order to streamline the continuing search of CEP in the RHIC low energy scan program.« less

Cell population structure prior to bifurcation predicts efficiency of directed differentiation in human induced pluripotent cells

PubMed Central

Bargaje, Rhishikesh; Trachana, Kalliopi; Shelton, Martin N.; McGinnis, Christopher S.; Zhou, Joseph X.; Chadick, Cora; Cook, Savannah; Cavanaugh, Christopher; Huang, Sui; Hood, Leroy

2017-01-01

Steering the differentiation of induced pluripotent stem cells (iPSCs) toward specific cell types is crucial for patient-specific disease modeling and drug testing. This effort requires the capacity to predict and control when and how multipotent progenitor cells commit to the desired cell fate. Cell fate commitment represents a critical state transition or “tipping point” at which complex systems undergo a sudden qualitative shift. To characterize such transitions during iPSC to cardiomyocyte differentiation, we analyzed the gene expression patterns of 96 developmental genes at single-cell resolution. We identified a bifurcation event early in the trajectory when a primitive streak-like cell population segregated into the mesodermal and endodermal lineages. Before this branching point, we could detect the signature of an imminent critical transition: increase in cell heterogeneity and coordination of gene expression. Correlation analysis of gene expression profiles at the tipping point indicates transcription factors that drive the state transition toward each alternative cell fate and their relationships with specific phenotypic readouts. The latter helps us to facilitate small molecule screening for differentiation efficiency. To this end, we set up an analysis of cell population structure at the tipping point after systematic variation of the protocol to bias the differentiation toward mesodermal or endodermal cell lineage. We were able to predict the proportion of cardiomyocytes many days before cells manifest the differentiated phenotype. The analysis of cell populations undergoing a critical state transition thus affords a tool to forecast cell fate outcomes and can be used to optimize differentiation protocols to obtain desired cell populations. PMID:28167799

Does sex induce a phase transition?

NASA Astrophysics Data System (ADS)

de Oliveira, P. M. C.; Moss de Oliveira, S.; Stauffer, D.; Cebrat, S.; Pękalski, A.

2008-05-01

We discovered a dynamic phase transition induced by sexual reproduction. The dynamics is a pure Darwinian rule applied to diploid bit-strings with both fundamental ingredients to drive Darwin's evolution: (1) random mutations and crossings which act in the sense of increasing the entropy (or diversity); and (2) selection which acts in the opposite sense by limiting the entropy explosion. Selection wins this competition if mutations performed at birth are few enough, and thus the wild genotype dominates the steady-state population. By slowly increasing the average number m of mutations, however, the population suddenly undergoes a mutational degradation precisely at a transition point mc. Above this point, the “bad” alleles (represented by 1-bits) spread over the genetic pool of the population, overcoming the selection pressure. Individuals become selectively alike, and evolution stops. Only below this point, m < mc, evolutionary life is possible. The finite-size-scaling behaviour of this transition is exhibited for large enough “chromosome” lengths L, through lengthy computer simulations. One important and surprising observation is the L-independence of the transition curves, for large L. They are also independent on the population size. Another is that mc is near unity, i.e. life cannot be stable with much more than one mutation per diploid genome, independent of the chromosome length, in agreement with reality. One possible consequence is that an eventual evolutionary jump towards larger L enabling the storage of more genetic information would demand an improved DNA copying machinery in order to keep the same total number of mutations per offspring.

The Effects of Thermal History on Nucleation of Tetragonal Lysozyme Crystals, or Hot Protein and Cold Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael; Judge, Russell; Pusey, Marc

2000-01-01

Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.2 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubilities are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to addition of precipitant solution. Warming a lysozyme solution above the phase transition point, then cooling it back below this point, has been shown to affect the subsequent nucleation rate, as determined by the numbers and size of crystals formed, but not the growth rate for the tetragonal crystal form . We have now measured the kinetics of this process and investigated its reversibility. The transition effects are progressive with temperature, having a half time of about 1 hour at 37C at pH 4.8. After holding a lysozyme solution at 37C (prior to addition of precipitant) for 16 hours, then cooling it back to 4C no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. Putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. This differential behaviour may be exploited to elucidate how and where flow affects the lysozyme crystal growth process. The presentation will focus on the results of these and ongoing studies in this area.

Theory-Based Predictors of Follow-Up Exercise Behavior After A Supervised Exercise Intervention in Older Breast Cancer Survivors

PubMed Central

Loprinzi, Paul D.; Cardinal, Bradley J.; Si, Qi; Bennett, Jill A.; Winters-Stone, Kerri

2014-01-01

Purpose Supervised exercise interventions can elicit numerous positive health outcomes in older breast cancer survivors. However, to maintain these benefits, regular exercise needs to be maintained long after the supervised program. This may be difficult, as in this transitional period (i.e., time period immediately following a supervised exercise program), breast cancer survivors are in the absence of on-site direct supervision from a trained exercise specialist. The purpose of the present study was to identify key determinants of regular exercise participation during a 6-month follow-up period after a 12-month supervised exercise program among women aged 65+ years who had completed adjuvant treatment for breast cancer. Methods At the conclusion of a supervised exercise program, and 6-months later, 69 breast cancer survivors completed surveys examining their exercise behavior and key constructs from the Transtheoretical Model. Results After adjusting for weight status and physical activity at the transition point, breast cancer survivors with higher self-efficacy at the point of transition were more likely to be active 6-months after leaving the supervised exercise program (OR [95% CI]: 1.10 [1.01–1.18]). Similarly, breast cancer survivors with higher behavioral processes of change use at the point of transition were more likely to be active (OR [95% CI]: 1.13 [1.02–1.26]). Conclusion These findings suggest that self-efficacy and the behavioral processes of change, in particular, play an important role in exercise participation during the transition from a supervised to a home-based program among older breast cancer survivors. PMID:22252545

Critical phenomena and chemical potential of a charged AdS black hole

NASA Astrophysics Data System (ADS)

Wei, Shao-Wen; Liang, Bin; Liu, Yu-Xiao

2017-12-01

Inspired by the interpretation of the cosmological constant from the boundary gauge theory, we here treat it as the number of colors N and its conjugate quantity as the associated chemical potential μ in the black hole side. Then the thermodynamics and the chemical potential for a five-dimensional charged AdS black hole are studied. It is found that there exists a small-large black hole phase transition of van der Waals type. The critical phenomena are investigated in the N2-μ chart. The result implies that the phase transition can occur for large number of colors N , while is forbidden for small number. This to some extent implies that the interaction of the system increases with the number. In particular, in the reduced parameter space, all the thermodynamic quantities can be rescaled with the black hole charge such that these reduced quantities are charge-independent. Then we obtain the coexistence curve and the phase diagram. The latent heat is also numerically calculated. Moreover, the heat capacity and the thermodynamic scalar are studied. The result indicates that the information of the first-order black hole phase transition is encoded in the heat capacity and scalar. However, the phase transition point cannot be directly calculated with them. Nevertheless, the critical point linked to a second-order phase transition can be determined by either the heat capacity or the scalar. In addition, we calculate the critical exponents of the heat capacity and the scalar for the saturated small and large black holes near the critical point.

Dual structural transition in small nanoparticles of Cu-Au alloy

NASA Astrophysics Data System (ADS)

Gafner, Yuri; Gafner, Svetlana; Redel, Larisa; Zamulin, Ivan

2018-02-01

Cu-Au alloy nanoparticles are known to be widely used in the catalysis of various chemical reactions as it was experimentally defined that in many cases the partial substitution of copper with gold increases catalytic activity. However, providing the reaction capacity of alloy nanoparticles the surface electronic structure strongly depends on their atomic ordering. Therefore, to theoretically determine catalytic properties, one needs to use a most real structural model complying with Cu-Au nanoparticles under various external influences. So, thermal stability limits were studied for the initial L12 phase in Cu3Au nanoalloy clusters up to 8.0 nm and Cu-Au clusters up to 3.0 nm at various degrees of Au atom concentration, with molecular dynamics method using a modified tight-binding TB-SMA potential. Dual structural transition L12 → FCC and further FCC → Ih is shown to be possible under the thermal factor in Cu3Au and Cu-Au clusters with the diameter up to 3.0 nm. The temperature of the structural transition FCC → Ih is established to decrease for small particles of Cu-Au alloy under the increase of Au atom concentration. For clusters with this structural transition, the melting point is found to be a linear increasing function of concentration, and for clusters without FCC → Ih structural transition, the melting point is a linear decreasing function of Au content. Thus, the article shows that doping Cu nanoclusters with Au atoms allows to control the forming structure as well as the melting point.

Computational studies of thermal and quantum phase transitions approached through non-equilibrium quenching

NASA Astrophysics Data System (ADS)

Liu, Cheng-Wei

Phase transitions and their associated critical phenomena are of fundamental importance and play a crucial role in the development of statistical physics for both classical and quantum systems. Phase transitions embody diverse aspects of physics and also have numerous applications outside physics, e.g., in chemistry, biology, and combinatorial optimization problems in computer science. Many problems can be reduced to a system consisting of a large number of interacting agents, which under some circumstances (e.g., changes of external parameters) exhibit collective behavior; this type of scenario also underlies phase transitions. The theoretical understanding of equilibrium phase transitions was put on a solid footing with the establishment of the renormalization group. In contrast, non-equilibrium phase transition are relatively less understood and currently a very active research topic. One important milestone here is the Kibble-Zurek (KZ) mechanism, which provides a useful framework for describing a system with a transition point approached through a non-equilibrium quench process. I developed two efficient Monte Carlo techniques for studying phase transitions, one is for classical phase transition and the other is for quantum phase transitions, both are under the framework of KZ scaling. For classical phase transition, I develop a non-equilibrium quench (NEQ) simulation that can completely avoid the critical slowing down problem. For quantum phase transitions, I develop a new algorithm, named quasi-adiabatic quantum Monte Carlo (QAQMC) algorithm for studying quantum quenches. I demonstrate the utility of QAQMC quantum Ising model and obtain high-precision results at the transition point, in particular showing generalized dynamic scaling in the quantum system. To further extend the methods, I study more complex systems such as spin-glasses and random graphs. The techniques allow us to investigate the problems efficiently. From the classical perspective, using the NEQ approach I verify the universality class of the 3D Ising spin-glasses. I also investigate the random 3-regular graphs in terms of both classical and quantum phase transitions. I demonstrate that under this simulation scheme, one can extract information associated with the classical and quantum spin-glass transitions without any knowledge prior to the simulation.

Time and Energy, Exploring Trajectory Options Between Nodes in Earth-Moon Space

NASA Technical Reports Server (NTRS)

Martinez, Roland; Condon, Gerald; Williams, Jacob

2012-01-01

The Global Exploration Roadmap (GER) was released by the International Space Exploration Coordination Group (ISECG) in September of 2011. It describes mission scenarios that begin with the International Space Station and utilize it to demonstrate necessary technologies and capabilities prior to deployment of systems into Earth-Moon space. Deployment of these systems is an intermediate step in preparation for more complex deep space missions to near-Earth asteroids and eventually Mars. In one of the scenarios described in the GER, "Asteroid Next", there are activities that occur in Earth-Moon space at one of the Earth-Moon Lagrange (libration) points. In this regard, the authors examine the possible role of an intermediate staging point in an effort to illuminate potential trajectory options for conducting missions in Earth-Moon space of increasing duration, ultimately leading to deep space missions. This paper will describe several options for transits between Low Earth Orbit (LEO) and the libration points, transits between libration points, and transits between the libration points and interplanetary trajectories. The solution space provided will be constrained by selected orbital mechanics design techniques and physical characteristics of hardware to be used in both crewed missions and uncrewed missions. The relationships between time and energy required to transfer hardware between these locations will provide a better understanding of the potential trade-offs mission planners could consider in the development of capabilities, individual missions, and mission series in the context of the ISECG GER.

Candidate Elastic Quantum Critical Point in LaCu 6 - x Au x

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poudel, Lekh; May, Andrew F.; Koehler, Michael R.

2016-11-30

In this paper, the structural properties of LaCu 6-xAu x are studied using neutron diffraction, x-ray diffraction, and heat capacity measurements. The continuous orthorhombic-monoclinic structural phase transition in LaCu 6 is suppressed linearly with Au substitution until a complete suppression of the structural phase transition occurs at the critical composition x c=0.3. Heat capacity measurements at low temperatures indicate residual structural instability at x c. The instability is ferroelastic in nature, with density functional theory calculations showing negligible coupling to electronic states near the Fermi level. Finally, the data and calculations presented here are consistent with the zero temperature terminationmore » of a continuous structural phase transition suggesting that the LaCu 6-xAu x series hosts an elastic quantum critical point.« less

Turkey Country Analysis Brief

EIA Publications

2017-01-01

Turkey is well placed to serve as a hub for oil and natural gas supply headed to Europe and other Atlantic markets from Russia, the Caspian region, and the Middle East. Turkey has been a major transit point for oil and is becoming more important as a transit point for natural gas. Growing volumes of Caspian oil are being sent to Black Sea ports such as Novorossisyk, Russia and Supsa, Georgia and then to Western markets by tanker via the Turkish Straits (Bosporus and Dardanelles waterways). Caspian oil and oil from northern Iraq also cross Turkey by pipeline, through the Ceyhan oil terminal on Turkey's Mediterranean coast.

Molecular dynamics study of melting and fcc-bcc transitions in Xe.

PubMed

Belonoshko, A B; Ahuja, R; Johansson, B

2001-10-15

We have investigated the phase diagram of Xe over a wide pressure-temperature range by molecular dynamics. The calculated melting curve is in good agreement with earlier experimental data. At a pressure of around 25 GPa and a temperature of about 2700 K we find a triple fcc-bcc liquid point. The calculated fcc-bcc boundary is in nice agreement with the experimental points, which, however, were interpreted as melting. This finding suggests that the transition from close-packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated.

Radiation-damage-induced transitions in zircon: Percolation theory applied to hardness and elastic moduli as a function of density

NASA Astrophysics Data System (ADS)

Beirau, Tobias; Nix, William D.; Ewing, Rodney C.; Pöllmann, Herbert; Salje, Ekhard K. H.

2018-05-01

Two in literature predicted percolation transitions in radiation-damaged zircon (ZrSiO4) were observed experimentally by measurement of the indentation hardness as a function of density and their correlation with the elastic moduli. Percolations occur near 30% and 70% amorphous fractions, where hardness deviates from its linear correlation with the elastic modulus (E), the shear modulus (G) and the bulk modulus (K). The first percolation point pc1 generates a cusp in the hardness versus density evolution, while the second percolation point is seen as a change of slope.

49 CFR Appendix A to Part 611 - Description of Measures Used for Project Evaluation.

Code of Federal Regulations, 2011 CFR

2011-10-01

... within 1/2-mile of boarding points associated with the proposed system increment. (b) Environmental... in British Thermal Units (BTU), compared to the baseline alternative; and (3) Current Environmental...) Transit-supportive corridor policies; (5) Supportive zoning regulations near transit stations; (6) Tools...

The Interplay between Language, Gesture, and Affect during Communicative Transition: A Dynamic Systems Approach

ERIC Educational Resources Information Center

Parlade, Meaghan V.; Iverson, Jana M.

2011-01-01

From a dynamic systems perspective, transition points in development are times of increased instability, during which behavioral patterns are susceptible to temporary decoupling. This study investigated the impact of the vocabulary spurt on existing patterns of communicative coordination. Eighteen typically developing infants were videotaped at…

Theory of the vortex matter transformations in high-Tc superconductor YBCO.

PubMed

Li, Dingping; Rosenstein, Baruch

2003-04-25

Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.

Measurement of Exciton Binding Energy of Monolayer WS2

NASA Astrophysics Data System (ADS)

Chen, Xi; Zhu, Bairen; Cui, Xiaodong

Excitonic effects are prominent in monolayer crystal of transition metal dichalcogenides (TMDCs) because of spatial confinement and reduced Coulomb screening. Here we use linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE) to measure the exciton binding energy of monolayer WS2. Peaks for excitonic absorptions of the direct gap located at K valley of the Brillouin zone and transitions from multiple points near Γ point of the Brillouin zone, as well as trion side band are shown in the linear absorption spectra of WS2. But there is no gap between distinct excitons and the continuum of the interband transitions. Strong electron-phonon scattering, overlap of excitons around Γ point and the transfer of the oscillator strength from interband continuum to exciton states make it difficult to resolve the electronic interband transition edge even down to 10K. The gap between excited states of the band-edge exciton and the single-particle band is probed by TP-PLE measurements. And the energy difference between 1s exciton and the single-particle gap gives the exciton binding energy of monolayer WS2 to be about 0.71eV. The work is supported by Area of excellency (AoE/P-04/08), CRF of Hong Kong Research Grant Council (HKU9/CRF/13G) and SRT on New Materials of The University of Hong Kong.

Getting Out of Silos: An Innovative Transitional Care Curriculum for Internal Medicine Residents Through Experiential Interdisciplinary Learning

PubMed Central

Schoenborn, Nancy L.; Christmas, Colleen

2013-01-01

Background Care transitions are common and highly vulnerable times during illness. Physicians need better training to improve care transitions. Existing transitional care curricula infrequently involve settings outside of the hospital or other health care disciplines. Intervention We created a curriculum to teach internal medicine residents how to provide better transitional care at hospital discharge through experiential, interdisciplinary learning in different care settings outside of the acute hospital, and we engaged other health care disciplines frequently involved in care transitions. Setting/Participants Nineteen postgraduate year-1 internal medicine trainees at an academic medical center in an urban location completed experiences in a postacute care facility, home health care, and outpatient clinics. Program Description The 2-week required curriculum involved teachers from geriatric medicine; physical, occupational, and speech therapy; and home health care, with both didactic and experiential components and self-reflective exercises. Program Evaluation The curriculum was highly rated (6.86 on a 9-point scale) and was associated with a significant increase in the rating of the overall quality of transitional care education (from 4.09 on a 5-point scale in 2011 to 4.53 in 2012) on the annual residency program survey. Learners reported improved knowledge in key curricular areas and that they would change practice as a result of the curriculum. Conclusions Our transitional care curriculum for internal medicine residents provides exposure to care settings and health care disciplines that patients frequently encounter. The curriculum has shown positive, short-term effects on learners' perceived knowledge and behavior. PMID:24455024

Transition and Turbulence Modeling for Blunt-Body Wake Flows

NASA Technical Reports Server (NTRS)

Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.

1997-01-01

This study attempts t o improve the modeling and computational prediction of high- speed transitional wake flows. The recently developed kappa - zeta (Enstrophy) turbulence model is coupled with a newly developed transition prediction method and implemented in an implicit flow solver well-suited to hypersonic flows. In this model, transition onset is determined as part of the solution. Results obtained using the new model for a 70- deg blunted cone/sting geometry demonstrate better agreement with experimental heat- transfer measurements when compared to laminar calculations as well as solutions using the kappa - omega model. Results are also presented for the situation where transition onset is preselected. It is shown that, in this case, results are quite sensitive to location of the transition point.

Comparison of molecular orientation and phase transition behaviors in the two kinds of ordered ultrathin films of reversed duckweed polymer ES-3 studied by infrared grazing reflection-absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Qiang; Xu, Weiqing; Zhao, Bing

2003-03-01

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection-absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 °C for the former while near 80, 105 and 140 °C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again.

Exploratory Investigation of Failure Mechanisms in Transition Regions between Solid Laminates and X-cor(registered tm) Truss Sandwich

NASA Technical Reports Server (NTRS)

OBrien, T. Kevin; Paris, Isabelle L.

2004-01-01

Small sub-component specimens consisting of solid laminates at the ends that transition to X-cor(R) truss sandwich in the center, were tested in a combination of three point bending, uni-axial tension, and combined tension and bending. The failure process in the transition region was documented for each loading using digital video and high-resolution cameras. For the 3-point bending tests, most of the deformation occurred in the solid laminate regions on either end of the specimen. Some pin debonding from the skin of the X-cor(R) truss sandwich was observed in the transition region and was accompanied by audible "pings" throughout the loading. Tension loaded specimens failed in the sandwich skin in the middle of the gage length, accompanied by separation of the sandwich core from the back skin and by delamination between the top skin and bottom skin at the transition region. The pinging associated with pin debonding occurred as the load was increased. However, the frequency of the pinging exceeded any visual observations of pin debonding in the video of the transition region. For specimens tested in combined tension and bending, the greatest amount of pinging occurred during initial application of the axial load. High-resolution images in the transition region indicated that the pinging corresponded to pins debonding and buckling due to the through-thickness Poisson contraction of the specimen. This buckling continued to a much smaller extent as the transverse load was applied.

Phase transitions and reentrant phenomena in liquid crystals having both rigid and flexible intramolecular joints

NASA Astrophysics Data System (ADS)

Pyżuk, W.; Górecka, E.; Mieczkowski, J.; Przedmojski, J.

1992-07-01

Two series of liquid-crystalline compounds having three phenyl rings separated by flexible spacer —CH(CH{3})CH{2}—COO— and by rigid azo and azoxy group, were studied by DSC, optical and X-ray methods. For esters of dl-3-(4^{prime}-nitro)-phenylbutyric acid with 4^{prime}-alkoxy-phenylazo-phenol-4 having dodecyloxy or longer terminal chains, as well as for related azoxy compounds, a narrow (even below 5 K) reentrant or inverted nematic phase appearing between partly bilayer and monolayer smectics A was observed. For higher homologues of the azoxy series additional smectic phases appear, leading to the occurrence of new multicritical points, e.g. the critical end point Ad Cd N^re. On each of the lines, which separate nematic from smectic A phases, transitions are of weakly first or second-order and more than one tricritical point can occur. On the A{1} N/A{1} N^re line, a simple N A{1} tricritical point is observed at T_NI/T_AN = 0.834. The presence of further critical points depends on the components of the binary system involved. Four of the azoxy compounds studied undergo a second order phase transition between partly bilayer smectics, Ad and Cd. Such a transition is accompanied by a jumb in the specific heat, varying linearly with the length of the molecular tails. Various temperature dependences of the layer spacing in the Ad phase are observed for subsequent homologues from the azoxy series. Plusieurs cristaux liquides composés de trois groupements phényl séparés par un groupement —CH(CH{3})CH{2}—COO—, ainsi que par des groupements azo et azoxy, ont été examinés par AED, méthodes optiques et par rayons X. Pour des esters de l'acide dl-3-(4^{prime}-nitro)phénylbutyrique et de 4^{prime}-alkoxy-phénylazo-phénol-4 ayant comme terminaison une chaîne dodecyloxy ou bien plus longue, ainsi que pour des composés azoxy relatif, on observe (même au-dessous de 5 K) une étroite phase nématique réentrante ou inverse entre les phases smectiques : monocouche et partiellement bicouche. Pour des homologues plus longs dans la série des composés azoxy, on a constaté l'existence d'autres phases smectiques ce qui implique l'apparition, sur les diagrammes des phases, de nouveau points multicritiques, par exemple le point Ad Cd N^re. Sur chaque ligne séparant les phases smectiques A de la phase nématique les transitions sont faiblement du premier ordre ou du deuxième ordre ce qui mène dans certain cas à plus qu'un point tricritique. Sur la ligne A{1} N/A{1} N^re on observe à T_NI/T_AN = 0,834 un simple point tricritique N A{1} — l'apparition des autres dépend du choix des constituants du système binaire. Dans le cas de quatre composés azoxy on a constaté une transition du deuxième ordre entre les phases smectiques partiellement bicouches, Ad et Cd. La transition est accompagnée d'un brusque changement de la chaleur spécifique qui varie linéairement avec la longueur de la queue de la molécule. Pour des homologues suivants de la série des composés azoxy on observe différentes dépendances en température de la distance entre les couches de la phase Ad.

Hiatus hernia in healthy volunteers is associated with intrasphincteric reflux and cardiac mucosal lengthening without traditional reflux.

PubMed

Robertson, Elaine V; Derakhshan, Mohammad H; Wirz, Angela A; Mitchell, David R; Going, James J; Kelman, Andrew W; Ballantyne, Stuart A; McColl, Kenneth E L

2017-07-01

Hiatus hernia (HH) is a key mediator of gastro-oesophageal reflux disease but little is known about its significance in the general population. We studied the structure and function of the gastro-oesophageal junction in healthy volunteers with and without HH. We compared 15 volunteers with HH, detected by endoscopy or MRI scan, but without gastro-oesophageal reflux disease with 15 controls matched for age, gender and body weight. Jumbo biopsies were taken across the squamocolumnar junction (SCJ). High-resolution pH metry (12 sensors) and manometry (36 sensors) were performed upright and supine, before and after a meal. The SCJ was marked with an endoscopically placed clip and visualised fluoroscopically. Cardiac mucosa was longer in volunteers with HH (3.5 vs 2.5 mm, p=0.01). There was no excessive acid reflux 5 cm above the upper border of the lower oesophageal sphincter (LOS) in either group but those with HH had short segment reflux 11 mm above the pH transition point after the meal when supine (pH<4 for 5.5% vs 0.3% of time, p=0.01). The SCJ and pH transition point were proximally displaced within the gastro-oesophageal junction in those with HH versus controls (p<0.05). The pH transition point was proximal to the peak LOS pressure point in HH subjects but distal to it in controls after the meal (p<0.05). When supine, the postprandial pH transition point crossed the SCJ in those with HH (p=0.03). Healthy volunteers with HH have increased intrasphincteric reflux and lengthening of cardiac mucosa in the absence of traditional transsphincteric reflux. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Secondary Education in a Changing World: Reaching a Turning Point.

ERIC Educational Resources Information Center

Hunter, Eagan

1985-01-01

William Van Til's three proposed scenarios for the future of secondary education are examined 10 years later, and American education is found to have reached a critical point as it goes through a transition from one era to another. (DCS)

Temperature dependence of the interband critical points of bulk Ge and strained Ge on Si

NASA Astrophysics Data System (ADS)

Fernando, Nalin S.; Nunley, T. Nathan; Ghosh, Ayana; Nelson, Cayla M.; Cooke, Jacqueline A.; Medina, Amber A.; Zollner, Stefan; Xu, Chi; Menendez, Jose; Kouvetakis, John

2017-11-01

Epitaxial Ge layers on a Si substrate experience a tensile biaxial stress due to the difference between the thermal expansion coefficients of the Ge epilayer and the Si substrate, which can be measured using asymmetric X-ray diffraction reciprocal space maps. This stress depends on temperature and affects the band structure, interband critical points, and optical spectra. This manuscripts reports careful measurements of the temperature dependence of the dielectric function and the interband critical point parameters of bulk Ge and Ge epilayers on Si using spectroscopic ellipsometry from 80 to 780 K and from 0.8 to 6.5 eV. The authors find a temperature-dependent redshift of the E1 and E1 + Δ1 critical points in Ge on Si (relative to bulk Ge). This redshift can be described well with a model based on thermal expansion coefficients, continuum elasticity theory, and the deformation potential theory for interband transitions. The interband transitions leading to E0‧ and E2 critical points have lower symmetry and therefore are not affected by the stress.

Insight into the biological effects of acupuncture points by X-ray absorption fine structure.

PubMed

Liu, Chenglin; Liu, Qinghua; Zhang, Dongming; Liu, Wei; Yan, Xiaohui; Zhang, Xinyi; Oyanagi, Hiroyuki; Pan, Zhiyun; Hu, Fengchun; Wei, Shiqiang

2018-06-02

Exploration of the biological effects of transition metal ions in acupuncture points is essential to clarify the functional mechanism of acupuncture treatment. Here we show that in the SP6 acupuncture point (Sanyinjiao) the Fe ions are in a high-spin state of approximately t 2g 4.5 e g 1.5 in an Fe-N(O) octahedral crystal field. The Fe K-edge synchrotron radiation X-ray absorption fine structure results reveal that the Fe-N and Fe-O bond lengths in the SP6 acupuncture point are 2.05 and 2.13 Å, respectively, and are 0.05-0.10 Å longer than those in the surrounding tissue. The distorted atomic structure reduces the octahedral symmetry and weakens the crystal field around the Fe ions by approximately 0.3 eV, leading to the high-spin configuration of the Fe ions, which is favorable for strengthening the magnetotransport and oxygen transportation properties in the acupuncture point by the enhanced spin coherence. This finding might provide some insight into the microscopic effect of the atomic and electronic interactions of transition metal ions in the acupuncture point. Graphical Abstract ᅟ.

Diamond turning of thermoplastic polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, E.; Scattergood, R.O.

Single point diamond turning studies were made using a series of thermoplastic polymers with different glass transition temperatures. Variations in surface morphology and surface roughness were observed as a function of cutting speed. Lower glass transition temperatures facilitate smoother surface cuts and better surface finish. This can be attributed to the frictional heating that occurs during machining. Because of the very low glass transition temperatures in polymeric compared to inorganic glasses, the precision machining response can be very speed sensitive.

Bose–Einstein condensation versus Dicke–Hepp–Lieb transition in an optical cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piazza, Francesco, E-mail: francesco.piazza@ph.tum.de; Strack, Philipp; Zwerger, Wilhelm

We provide an exact solution for the interplay between Bose–Einstein condensation and the Dicke–Hepp–Lieb self-organization transition of an ideal Bose gas trapped inside a single-mode optical cavity and subject to a transverse laser drive. Based on an effective action approach, we determine the full phase diagram at arbitrary temperature, which features a bi-critical point where the transitions cross. We calculate the dynamically generated band structure of the atoms and the associated suppression of the critical temperature for Bose–Einstein condensation in the phase with a spontaneous periodic density modulation. Moreover, we determine the evolution of the polariton spectrum due to themore » coupling of the cavity photons and the atomic field near the self-organization transition, which is quite different above or below the Bose–Einstein condensation temperature. At low temperatures, the critical value of the Dicke–Hepp–Lieb transition decreases with temperature and thus thermal fluctuations can enhance the tendency to a periodic arrangement of the atoms. -- Highlights: •Atoms inside a driven cavity can undergo two transitions: self-organization and BEC. •The phase diagram has four phases which coexist at a bi-critical point. •Atom–cavity coupling creates a dynamical lattice for the atoms. •Finite temperature can enhance the tendency towards self-organization. •We calculate the detailed spectrum of the polaritonic excitations.« less

On the thermodynamics of the black hole and hairy black hole transitions in the asymptotically flat spacetime with a box

NASA Astrophysics Data System (ADS)

Peng, Yan; Wang, Bin; Liu, Yunqi

2018-03-01

We study the asymptotically flat quasi-local black hole/hairy black hole model with nonzero mass of the scalar field. We disclose effects of the scalar mass on transitions in a grand canonical ensemble with condensation behaviors of the parameter ψ 2, which is similar to approaches in holographic theories. We find that a more negative scalar mass makes the phase transition easier. We also obtain the analytical relation ψ 2∝ (Tc-T)^{1/2} around the critical phase transition points, implying a second order phase transition. Besides the parameter ψ 2, we show that metric solutions can be used to disclose properties of the transitions. In this work, we observe that phase transitions in a box are strikingly similar to holographic transitions in AdS gravity and the similarity provides insights into holographic theories.

Dependence of transition width on current and critical current in transition-edge sensors

NASA Astrophysics Data System (ADS)

Morgan, K. M.; Pappas, C. G.; Bennett, D. A.; Gard, J. D.; Hays-Wehle, J. P.; Hilton, G. C.; Reintsema, C. D.; Schmidt, D. R.; Ullom, J. N.; Swetz, D. S.

2017-05-01

In superconducting transition-edge sensor X-ray detectors, we observe that as the thermal conductance (G) to the heat bath increases, the resistive transition broadens. Consequently, the sensitivity of films to deposited energy worsens. Using a two-fluid model for the superconducting-to-normal transition in a thin film, we show that this broadening can be attributed to the larger current (I0) necessary for biasing the film at a given point in the transition for higher-G devices, resulting in a higher Ic0/I0 ratio (Ic0 is the film's critical current at zero temperature). To recover a sharper transition, we fabricated rectangular films with varying numbers of internal normal-metal structures while keeping G constant, allowing the independent variation of both I0 and Ic0. We show that it is possible to manipulate the transition width and G independently, thus enabling fast thermal sensors with an excellent energy resolution.

Transition Probabilities for Hydrogen-Like Atoms

NASA Astrophysics Data System (ADS)

Jitrik, Oliverio; Bunge, Carlos F.

2004-12-01

E1, M1, E2, M2, E3, and M3 transition probabilities for hydrogen-like atoms are calculated with point-nucleus Dirac eigenfunctions for Z=1-118 and up to large quantum numbers l=25 and n=26, increasing existing data more than a thousandfold. A critical evaluation of the accuracy shows a higher reliability with respect to previous works. Tables for hydrogen containing a subset of the results are given explicitly, listing the states involved in each transition, wavelength, term energies, statistical weights, transition probabilities, oscillator strengths, and line strengths. The complete results, including 1 863 574 distinct transition probabilities, lifetimes, and branching fractions are available at http://www.fisica.unam.mx/research/tables/spectra/1el

Ab initio computation of the transition temperature of the charge density wave transition in TiS e2

NASA Astrophysics Data System (ADS)

Duong, Dinh Loc; Burghard, Marko; Schön, J. Christian

2015-12-01

We present a density functional perturbation theory approach to estimate the transition temperature of the charge density wave transition of TiS e2 . The softening of the phonon mode at the L point where in TiS e2 a giant Kohn anomaly occurs, and the energy difference between the normal and distorted phase are analyzed. Both features are studied as functions of the electronic temperature, which corresponds to the Fermi-Dirac distribution smearing value in the calculation. The transition temperature is found to be 500 and 600 K by phonon and energy analysis, respectively, in reasonable agreement with the experimental value of 200 K.

Computer graphic visualization of orbiter lower surface boundary-layer transition

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.; Hartung, L. C.

1984-01-01

Computer graphic techniques are applied to the processing of Shuttle Orbiter flight data in order to create a visual presentation of the extent and movement of the boundary-layer transition front over the orbiter lower surface during entry. Flight-measured surface temperature-time histories define the onset and completion of the boundary-layer transition process at any measurement location. The locus of points which define the spatial position of the boundary-layer transition front on the orbiter planform is plotted at each discrete time for which flight data are available. Displaying these images sequentially in real-time results in an animated simulation of the in-flight boundary-layer transition process.

Dating Violence, Bullying, and Sexual Harassment: Longitudinal Profiles and Transitions over Time

ERIC Educational Resources Information Center

Miller, Shari; Williams, Jason; Cutbush, Stacey; Gibbs, Deborah; Clinton-Sherrod, Monique; Jones, Sarah

2013-01-01

Although there is growing recognition of the problem of dating violence, little is known about how it unfolds among young adolescents who are just beginning to date. This study examined classes (subgroups) and transitions between classes over three time points based on dating violence, bullying, and sexual harassment perpetration and victimization…

Topic Transition in Educational Videos Using Visually Salient Words

ERIC Educational Resources Information Center

Gandhi, Ankit; Biswas, Arijit; Deshmukh, Om

2015-01-01

In this paper, we propose a visual saliency algorithm for automatically finding the topic transition points in an educational video. First, we propose a method for assigning a saliency score to each word extracted from an educational video. We design several mid-level features that are indicative of visual saliency. The optimal feature combination…

Negotiating with Tradition: Curriculum Reform and Institutional Transition in a Conservatoire

ERIC Educational Resources Information Center

Duffy, Celia

2013-01-01

The Royal Conservatoire of Scotland has recently transformed its curriculum through a process of curriculum reform. This has been a major institutional transition and has challenged many of the traditional practices of the conservatoire. Taking the global thinking on curriculum reform as its starting point, the conservatoire’s aspiration has been…

Points of Transition: Understanding the Constructed Identities of L2 Learners/Users across Time and Space

ERIC Educational Resources Information Center

Adawu, Anthony; Martin-Beltran, Melinda

2012-01-01

Using sociocultural and poststructuralist theoretical lenses, this study examines the narrative construction of language-learner identity across time and space. We applied cross-narrative methodologies to analyze language-learning autobiographies and interview data from three English users who had recently transitioned to a U.S. context for…

Probing topological order with Rényi entropy

NASA Astrophysics Data System (ADS)

Halász, Gábor B.; Hamma, Alioscia

2012-12-01

We present an analytical study of the quantum phase transition between the topologically ordered toric-code-model ground state and the disordered spin-polarized state. The phase transition is induced by applying an external magnetic field, and the variation in topological order is detected via two nonlocal quantities: the Wilson loop and the topological Rényi entropy of order 2. By exploiting an equivalence with the transverse-field Ising model and considering two different variants of the problem, we investigate the field dependence of these quantities by means of an exact treatment in the exactly solvable variant and complementary perturbation theories around the limits of zero and infinite fields in both variants. We find strong evidence that the phase transition point between topological order and disorder is marked by a discontinuity in the topological Rényi entropy and that the two phases around the phase transition point are characterized by its different constant values. Our results therefore indicate that the topological Rényi entropy is a proper topological invariant: its allowed values are discrete and can be used to distinguish between different phases of matter.

Dynamical predictors of an imminent phenotypic switch in bacteria

NASA Astrophysics Data System (ADS)

Wang, Huijing; Ray, J. Christian J.

2017-08-01

Single cells can stochastically switch across thresholds imposed by regulatory networks. Such thresholds can act as a tipping point, drastically changing global phenotypic states. In ecology and economics, imminent transitions across such tipping points can be predicted using dynamical early warning indicators. A typical example is ‘flickering’ of a fast variable, predicting a longer-lasting switch from a low to a high state or vice versa. Considering the different timescales between metabolite and protein fluctuations in bacteria, we hypothesized that metabolic early warning indicators predict imminent transitions across a network threshold caused by enzyme saturation. We used stochastic simulations to determine if flickering predicts phenotypic transitions, accounting for a variety of molecular physiological parameters, including enzyme affinity, burstiness of enzyme gene expression, homeostatic feedback, and rates of metabolic precursor influx. In most cases, we found that metabolic flickering rates are robustly peaked near the enzyme saturation threshold. The degree of fluctuation was amplified by product inhibition of the enzyme. We conclude that sensitivity to flickering in fast variables may be a possible natural or synthetic strategy to prepare physiological states for an imminent transition.

Monte-Carlo simulations of the clean and disordered contact process in three space dimensions

NASA Astrophysics Data System (ADS)

Vojta, Thomas

2013-03-01

The absorbing-state transition in the three-dimensional contact process with and without quenched randomness is investigated by means of Monte-Carlo simulations. In the clean case, a reweighting technique is combined with a careful extrapolation of the data to infinite time to determine with high accuracy the critical behavior in the three-dimensional directed percolation universality class. In the presence of quenched spatial disorder, our data demonstrate that the absorbing-state transition is governed by an unconventional infinite-randomness critical point featuring activated dynamical scaling. The critical behavior of this transition does not depend on the disorder strength, i.e., it is universal. Close to the disordered critical point, the dynamics is characterized by the nonuniversal power laws typical of a Griffiths phase. We compare our findings to the results of other numerical methods, and we relate them to a general classification of phase transitions in disordered systems based on the rare region dimensionality. This work has been supported in part by the NSF under grants no. DMR-0906566 and DMR-1205803.

Singlet-catalyzed electroweak phase transitions in the 100 TeV frontier

NASA Astrophysics Data System (ADS)

Kotwal, Ashutosh V.; Ramsey-Musolf, Michael J.; No, Jose Miguel; Winslow, Peter

2016-08-01

We study the prospects for probing a gauge singlet scalar-driven strong first-order electroweak phase transition with a future proton-proton collider in the 100 TeV range. Singlet-Higgs mixing enables resonantly enhanced di-Higgs production, potentially aiding discovery prospects. We perform Monte Carlo scans of the parameter space to identify regions associated with a strong first-order electroweak phase transition, analyze the corresponding di-Higgs signal, and select a set of benchmark points that span the range of di-Higgs signal strengths. For the b b ¯γ γ and 4 τ final states, we investigate discovery prospects for each benchmark point for the high-luminosity phase of the Large Hadron Collider and for a future p p collider with √{s }=50 , 100, or 200 TeV. We find that any of these future collider scenarios could significantly extend the reach beyond that of the high-luminosity LHC, and that with √{s }=100 TeV (200 TeV) and 30 ab-1 , the full region of parameter space favorable to strong first-order electroweak phase transitions is almost fully (fully) discoverable.

Critical scaling of the mutual information in two-dimensional disordered Ising models

NASA Astrophysics Data System (ADS)

Sriluckshmy, P. V.; Mandal, Ipsita

2018-04-01

Rényi mutual information, computed from second Rényi entropies, can identify classical phase transitions from their finite-size scaling at critical points. We apply this technique to examine the presence or absence of finite temperature phase transitions in various two-dimensional models on a square lattice, which are extensions of the conventional Ising model by adding a quenched disorder. When the quenched disorder causes the nearest neighbor bonds to be both ferromagnetic and antiferromagnetic, (a) a spin glass phase exists only at zero temperature, and (b) a ferromagnetic phase exists at a finite temperature when the antiferromagnetic bond distributions are sufficiently dilute. Furthermore, finite temperature paramagnetic-ferromagnetic transitions can also occur when the disordered bonds involve only ferromagnetic couplings of random strengths. In our numerical simulations, the ‘zero temperature only’ phase transitions are identified when there is no consistent finite-size scaling of the Rényi mutual information curves, while for finite temperature critical points, the curves can identify the critical temperature T c by their crossings at T c and 2 Tc .

Using optimal transport theory to estimate transition probabilities in metapopulation dynamics

USGS Publications Warehouse

Nichols, Jonathan M.; Spendelow, Jeffrey A.; Nichols, James D.

2017-01-01

This work considers the estimation of transition probabilities associated with populations moving among multiple spatial locations based on numbers of individuals at each location at two points in time. The problem is generally underdetermined as there exists an extremely large number of ways in which individuals can move from one set of locations to another. A unique solution therefore requires a constraint. The theory of optimal transport provides such a constraint in the form of a cost function, to be minimized in expectation over the space of possible transition matrices. We demonstrate the optimal transport approach on marked bird data and compare to the probabilities obtained via maximum likelihood estimation based on marked individuals. It is shown that by choosing the squared Euclidean distance as the cost, the estimated transition probabilities compare favorably to those obtained via maximum likelihood with marked individuals. Other implications of this cost are discussed, including the ability to accurately interpolate the population's spatial distribution at unobserved points in time and the more general relationship between the cost and minimum transport energy.

Control of stationary crossflow modes in swept Hiemenz flows with dielectric barrier discharge plasma actuators

NASA Astrophysics Data System (ADS)

Wang, Zhefu; Wang, Liang; Fu, Song

2017-09-01

Sensitivity analyses and non-linear parabolized stability equations are solved to provide a computational assessment of the potential use of a Dielectric Barrier Discharge (DBD) plasma actuator for a prolonging laminar region in swept Hiemenz flow. The derivative of the kinetic energy with respect to the body force is deduced, and its components in different directions are defined as sensitivity functions. The results of sensitivity analyses and non-linear parabolized stability equations both indicate that the introduction of a body force as the plasma actuator at the bottom of a crossflow vortex can mitigate instability to delay flow transition. In addition, the actuator is more effective when placed more upstream until the neutral point. In fact, if the actuator is sufficiently close to the neutral point, it is likely to act as a strong disturbance over-riding the natural disturbance and dominating transition. Different operating voltages of the DBD actuators are tested, resulting in an optimal practice for transition delay. The results demonstrate that plasma actuators offer great potential for transition control.

Transition and mixing in axisymmetric jets and vortex rings

NASA Technical Reports Server (NTRS)

Allen, G. A., Jr.; Cantwell, B. J.

1986-01-01

A class of impulsively started, axisymmetric, laminar jets produced by a time dependent joint source of momentum are considered. These jets are different flows, each initially at rest in an unbounded fluid. The study is conducted at three levels of detail. First, a generalized set of analytic creeping flow solutions are derived with a method of flow classification. Second, from this set, three specific creeping flow solutions are studied in detail: the vortex ring, the round jet, and the ramp jet. This study involves derivation of vorticity, stream function, entrainment diagrams, and evolution of time lines through computer animation. From entrainment diagrams, critical points are derived and analyzed. The flow geometry is dictated by the properties and location of critical points which undergo bifurcation and topological transformation (a form of transition) with changing Reynolds number. Transition Reynolds numbers were calculated. A state space trajectory was derived describing the topological behavior of these critical points. This state space derivation yielded three states of motion which are universal for all axisymmetric jets. Third, the axisymmetric round jet is solved numerically using the unsteady laminar Navier Stokes equations. These equations were shown to be self similar for the round jet. Numerical calculations were performed up to a Reynolds number of 30 for a 60x60 point mesh. Animations generated from numerical solution showed each of the three states of motion for the round jet, including the Re = 30 case.

The possibility of a tipping point in the Arctic sea ice cover, and associated early-warning signals

NASA Astrophysics Data System (ADS)

Jastamin Steene, Rebekka

2017-04-01

As the Arctic sea ice has become one of the primer indicators of global climate change, with a seemingly accelerated loss in both ice extent and volume the latest decades, the existence of a tipping point related to the Arctic sea ice cover has been widely debated. Several observed and potential abrupt transitions in the climate system may be interpreted as bifurcations in randomly driven dynamical systems. This means that a system approaching a bifurcation point shifts from one stable state to another, and we say that the system is subject to a critical transition. As the equilibrium states become unstable in the vicinity of a bifurcation point the characteristic relaxation times increases, and the system is said to experience a "critical slowing down". This makes it plausible to observe so called early-warning signals (EWS) when approaching a critical transition. In the Arctic non-linear mechanisms like the temperature response of the ice-albedo feedback can potentially cause a sudden shift to an ice-free Arctic Ocean. Using bifurcation theory and potential analyses we examine time series of observational data of the Arctic sea ice, investigating the possibility of multiple states in the behavior of the ice cover. We further debate whether a shift between states is irreversible, and whether it can be preluded by early-warning signals.

On the correlation between hydrogen bonding and melting points in the inositols

PubMed Central

Bekö, Sándor L.; Alig, Edith; Schmidt, Martin U.; van de Streek, Jacco

2014-01-01

Inositol, 1,2,3,4,5,6-hexahydroxycyclohexane, exists in nine stereoisomers with different crystal structures and melting points. In a previous paper on the relationship between the melting points of the inositols and the hydrogen-bonding patterns in their crystal structures [Simperler et al. (2006 ▶). CrystEngComm 8, 589], it was noted that although all inositol crystal structures known at that time contained 12 hydrogen bonds per molecule, their melting points span a large range of about 170 °C. Our preliminary investigations suggested that the highest melting point must be corrected for the effect of molecular symmetry, and that the three lowest melting points may need to be revised. This prompted a full investigation, with additional experiments on six of the nine inositols. Thirteen new phases were discovered; for all of these their crystal structures were examined. The crystal structures of eight ordered phases could be determined, of which seven were obtained from laboratory X-ray powder diffraction data. Five additional phases turned out to be rotator phases and only their unit cells could be determined. Two previously unknown melting points were measured, as well as most enthalpies of melting. Several previously reported melting points were shown to be solid-to-solid phase transitions or decomposition points. Our experiments have revealed a complex picture of phases, rotator phases and phase transitions, in which a simple correlation between melting points and hydrogen-bonding patterns is not feasible. PMID:25075320

Efimov-driven phase transitions of the unitary Bose gas.

PubMed

Piatecki, Swann; Krauth, Werner

2014-03-20

Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of 'unitary' interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

Hero's journey in bifurcation diagram

NASA Astrophysics Data System (ADS)

Monteiro, L. H. A.; Mustaro, P. N.

2012-06-01

The hero's journey is a narrative structure identified by several authors in comparative studies on folklore and mythology. This storytelling template presents the stages of inner metamorphosis undergone by the protagonist after being called to an adventure. In a simplified version, this journey is divided into three acts separated by two crucial moments. Here we propose a discrete-time dynamical system for representing the protagonist's evolution. The suffering along the journey is taken as the control parameter of this system. The bifurcation diagram exhibits stationary, periodic and chaotic behaviors. In this diagram, there are transition from fixed point to chaos and transition from limit cycle to fixed point. We found that the values of the control parameter corresponding to these two transitions are in quantitative agreement with the two critical moments of the three-act hero's journey identified in 10 movies appearing in the list of the 200 worldwide highest-grossing films.

Phase transition of charged-AdS black holes and quasinormal modes: A time domain analysis

NASA Astrophysics Data System (ADS)

Chabab, M.; El Moumni, H.; Iraoui, S.; Masmar, K.

2017-10-01

In this work, we investigate the time evolution of a massless scalar perturbation around small and large RN-AdS4 black holes for the purpose of probing the thermodynamic phase transition. We show that below the critical point the scalar perturbation decays faster with increasing of the black hole size, both for small and large black hole phases. Our analysis of the time profile of quasinormal mode reveals a sharp distinction between the behaviors of both phases, providing a reliable tool to probe the black hole phase transition. However at the critical point P=Pc, as the black hole size extends, we note that the damping time increases and the perturbation decays faster, the oscillation frequencies raise either in small and large black hole phase. In this case the time evolution approach fails to track the AdS4 black hole phase.

Analytic renormalized bipartite and tripartite quantum discords with quantum phase transition in XXZ spins chain

NASA Astrophysics Data System (ADS)

Joya, Wajid; Khan, Salman; Khalid Khan, M.; Alam, Sher

2017-05-01

The behavior of bipartite quantum discord (BQD) and tripartite quantum discord (TQD) in the Heisenberg XXZ spins chain is investigated with the increasing size of the system using the approach of the quantum renormalization group method. Analytical relations for both BQD and TQD are obtained and the results are checked through numerical optimization. In the thermodynamics limit, both types of discord exhibit quantum phase transition (QPT). The boundary of QPT links the phases of saturated discord and zero discord. The first derivative of both discords becomes discontinuous at the critical point, which corresponds to the second-order phase transition. Qualitatively identical, the amount of saturated BQD strongly depends on the relative positions of spins inside a block. TQD can be a better candidate than BQD both for analyzing QPT and implementing quantum information tasks. The scaling behavior in the vicinity of the critical point is discussed.

Bending light via adiabatic optical transition in longitudinally modulated photonic lattices

PubMed Central

Han, Bin; Xu, Lei; Dou, Yiling; Xu, Jingjun; Zhang, Guoquan

2015-01-01

Bending light in a controllable way is desired in various applications such as beam steering, navigating and cloaking. Different from the conventional way to bend light by refractive index gradient, transformation optics or special beams through wavefront design such as Airy beams and surface plasmons, we proposed a mechanism to bend light via resonant adiabatic optical transition between Floquet-Bloch (FB) modes from different FB bands in longitudinally modulated photonic lattices. The band structure of longitudinally modulated photonic lattices was calculated by employing the concept of quasi-energy based on the Floquet-Bloch theory, showing the existence of band discontinuities at specific resonant points which cannot be revealed by the coupled-mode theory. Interestingly, different FB bands can be seamlessly connected at these resonant points in longitudinally modulated photonic lattices driven by adiabatically varying the longitudinal modulation period along the propagation direction, which stimulates the adiabatic FB mode transition between different FB bands. PMID:26511890

Hugoniots of aerogels involving carbon and resorcinol formaldehyde

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hrubesh, L H; Ree, F H; Schmidt, R D

1999-06-24

Recently, a first-order phase transition is predicted in liquid carbon using atomistic simulation and Brenner's bond order potential. There are also experimental data suggesting a possibility for a first-order phase transition. In light of this, a thermochemical equilibrium code (CHEQ) is used to provide guidance to experiments to find a liquid-liquid phase change in carbon foam and carbon-rich aerogel, resorcinol formaldehyde. Isotherms and Hugoniots were computed based on the previous analysis by van Thiel and Ree. The present calculations predict the liquid-liquid-graphite triple point to be at 5000 K and 5.2 GPa and its critical point to be at 6000more » K and 8.8 GPa. The present Hugoniot calculations suggest that the liquid-liquid phase transition may be detected by performing a shock experiment with initial density of approximately 0.15 gm/cm{sup 3}.« less

Critical behavior of the extended Hubbard model with bond dimerization

NASA Astrophysics Data System (ADS)

Ejima, Satoshi; Lange, Florian; Essler, Fabian H. L.; Fehske, Holger

2018-05-01

Exploiting the matrix-product-state based density-matrix renormalization group (DMRG) technique we study the one-dimensional extended (U-V) Hubbard model with explicit bond dimerization in the half-filled band sector. In particular we investigate the nature of the quantum phase transition, taking place with growing ratio V / U between the symmetry-protected-topological and charge-density-wave insulating states. The (weak-coupling) critical line of continuous Ising transitions with central charge c = 1 / 2 terminates at a tricritical point belonging to the universality class of the dilute Ising model with c = 7 / 10 . We demonstrate that our DMRG data perfectly match with (tricritical) Ising exponents, e.g., for the order parameter β = 1 / 8 (1/24) and correlation length ν = 1 (5/9). Beyond the tricritical Ising point, in the strong-coupling regime, the quantum phase transition becomes first order.

Sensitivity study of experimental measures for the nuclear liquid-gas phase transition in the statistical multifragmentation model

NASA Astrophysics Data System (ADS)

Lin, W.; Ren, P.; Zheng, H.; Liu, X.; Huang, M.; Wada, R.; Qu, G.

2018-05-01

The experimental measures of the multiplicity derivatives—the moment parameters, the bimodal parameter, the fluctuation of maximum fragment charge number (normalized variance of Zmax, or NVZ), the Fisher exponent (τ ), and the Zipf law parameter (ξ )—are examined to search for the liquid-gas phase transition in nuclear multifragmention processes within the framework of the statistical multifragmentation model (SMM). The sensitivities of these measures are studied. All these measures predict a critical signature at or near to the critical point both for the primary and secondary fragments. Among these measures, the total multiplicity derivative and the NVZ provide accurate measures for the critical point from the final cold fragments as well as the primary fragments. The present study will provide a guide for future experiments and analyses in the study of the nuclear liquid-gas phase transition.

A Proof of the Occupancy Principle and the Mean-Transit-Time Theorem for Compartmental Models

PubMed Central

RAMAKRISHNAN, RAJASEKHAR; LEONARD, EDWARD F.; DELL, RALPH B.

2012-01-01

The occupancy principle and the mean-transit-time theorem are derived for the passage of a tracer through a system that can be described by a general pool model. It is proved, using matrix theory, that if (and only if) tracer entering the system labels equally all tracee fluxes into the system, then the integral of the tracer concentration is the same in all the pools. It is also proved that if, in addition, all flow out of the system is through the observation point, the first moment of the tracer concentration at the observation point can be used to calculate the total amount of trace in the system. The necessity of this condition is analyzed. Examples are given of models in which the occupancy principle and the mean-transit-time theorem hold or do not hold. PMID:22328793

Wake-sleep transition as a noisy bifurcation

NASA Astrophysics Data System (ADS)

Yang, Dong-Ping; McKenzie-Sell, Lauren; Karanjai, Angela; Robinson, P. A.

2016-08-01

A recent physiologically based model of the ascending arousal system is used to analyze the dynamics near the transition from wake to sleep, which corresponds to a saddle-node bifurcation at a critical point. A normal form is derived by approximating the dynamics by those of a particle in a parabolic potential well with dissipation. This mechanical analog is used to calculate the power spectrum of fluctuations in response to a white noise drive, and the scalings of fluctuation variance and spectral width are derived versus distance from the critical point. The predicted scalings are quantitatively confirmed by numerical simulations, which show that the variance increases and the spectrum undergoes critical slowing, both in accord with theory. These signals can thus serve as potential precursors to indicate imminent wake-sleep transition, with potential application to safety-critical occupations in transport, air-traffic control, medicine, and heavy industry.

Thermodynamic properties and p-T phase diagrams of (NH4)3M3+F6 cryolites (M3+: Ga, Sc)

NASA Astrophysics Data System (ADS)

Gorev, M. V.; Flerov, I. N.; Tressaud, A.

1999-10-01

Calorimetric and high pressure experiments are used to establish thermodynamic features of (NH4)3M3+F6 cryolites with M3+: Ga, Sc as they undergo one and three structural phase transitions, respectively. The heat capacity measurements performed between 80 K and 370 K, using an adiabatic calorimeter, have shown that all phase transitions under study are first order with different closeness to the tricritical point. The total entropy change in the Sc compound connected with the successive transformations is almost equal to the entropy change in the Ga cryolite. The effect of hydrostatic pressure has been studied up to 0.6 GPa, using differential thermographic analysis. The p-T phase diagrams of both cryolites were found to be rather complicated, including triple points. The experimental results are considered as connected with order-disorder phase transitions.

Phase transition and flow-rate behavior of merging granular flows.

PubMed

Hu, Mao-Bin; Liu, Qi-Yi; Jiang, Rui; Hou, Meiying; Wu, Qing-Song

2015-02-01

Merging of granular flows is ubiquitous in industrial, mining, and geological processes. However, its behavior remains poorly understood. This paper studies the phase transition and flow-rate behavior of two granular flows merging into one channel. When the main channel is wider than the side channel, the system shows a remarkable two-sudden-drops phenomenon in the outflow rate when gradually increasing the main inflow. When gradually decreasing the main inflow, the system shows obvious hysteresis phenomenon. We study the flow-rate-drop phenomenon by measuring the area fraction and the mean velocity at the merging point. The phase diagram of the system is also presented to understand the occurrence of the phenomenon. We find that the dilute-to-dense transition occurs when the area fraction of particles at the joint point exceeds a critical value ϕ(c)=0.65±0.03.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abgrall, N.; Arnquist, I. J.; Avignone, F. T.

Here, a search for Pauli-exclusion-principle-violating K α electron transitions was performed using 89.5 kg-d of data collected with a p-type point contact high-purity germanium detector operated at the Kimballton Underground Research Facility. A lower limit on the transition lifetime of 5.8 × 10 30 s at 90% C.L. was set by looking for a peak at 10.6 keV resulting from the X-ray and Auger electrons present following the transition. A similar analysis was done to look for the decay of atomic K-shell electrons into neutrinos, resulting in a lower limit of 6.8 × 10 30 s at 90% C.L. Itmore » is estimated that the Majorana Demonstrator, a 44 kg array of p-type point contact detectors that will search for the neutrinoless double-beta decay of 76Ge, could improve upon these exclusion limits by an order of magnitude after three years of operation.« less

School adjustment in sixth graders: parenting transitions, family climate, and peer norm effects.

PubMed

Kurdek, L A; Fine, M A; Sinclair, R J

1995-04-01

This study examined whether sixth graders' (mean age = 11.86 years) adjustment to the school context (assessed by grades, achievement scores, and disruptive behavior) was affected by factors from both the family context (represented by students' reports of the number of parenting transitions experienced as well as current levels of supervision, acceptance, autonomy granting, and conflict in the family) and the peer context (represented by students' perceptions of peer norms supporting academic excellence). School adjustment was related to the number of parenting transitions experienced, family climate, and peer norms as well as to higher-order relations involving family climate and peer norms such that (a) high grade point averages occurred at only moderate levels of family supervision, (b) achievement scores were positively related to supervision at only low levels of family autonomy granting, and (c) grade point average was positively related to peer norms at only high levels of family acceptance.

Saddle point localization of molecular wavefunctions.

PubMed

Mellau, Georg Ch; Kyuberis, Alexandra A; Polyansky, Oleg L; Zobov, Nikolai; Field, Robert W

2016-09-15

The quantum mechanical description of isomerization is based on bound eigenstates of the molecular potential energy surface. For the near-minimum regions there is a textbook-based relationship between the potential and eigenenergies. Here we show how the saddle point region that connects the two minima is encoded in the eigenstates of the model quartic potential and in the energy levels of the [H, C, N] potential energy surface. We model the spacing of the eigenenergies with the energy dependent classical oscillation frequency decreasing to zero at the saddle point. The eigenstates with the smallest spacing are localized at the saddle point. The analysis of the HCN ↔ HNC isomerization states shows that the eigenstates with small energy spacing relative to the effective (v1, v3, ℓ) bending potentials are highly localized in the bending coordinate at the transition state. These spectroscopically detectable states represent a chemical marker of the transition state in the eigenenergy spectrum. The method developed here provides a basis for modeling characteristic patterns in the eigenenergy spectrum of bound states.

A DFT study on the failure mechanism of Al2O3 film by various point defects in solution

NASA Astrophysics Data System (ADS)

Zhang, Chuan-Hui; Chen, Bao; Jin, Ying; Sun, Dong-Bai

2018-03-01

The defects on oxide film surface are very important, and they would occur when the film is peeled or scratched. The periodic DFT calculations have been performed on Al2O3 surface to model the influences of various point-defects. Three kinds of point defect surfaces (vacancy, inversion, substitution) are considered, and the molecular H2O dissociation and the transition state are calculated. The predicted formation energy of O vacancy is 8.30 eV, whereas that corresponding to the formation of Al vacancy is found to be at least a 55% larger. On the vacancy point defect surfaces, upward H2O molecule surfaces prefer to occur chemical reaction, leading the surfaces to be hydroxylated. And then the D-Cl-substitution-Al surface is corroded, which suggests a Cl adsorption induced failure mechanism of the oxide film. At last, the process of H2O dissociation on the OH-substitution-Al surfaces with four or five transition paths are discussed.

Continuous transition between weak and ultrastrong coupling through exceptional points in carbon nanotube microcavity exciton-polaritons

NASA Astrophysics Data System (ADS)

Gao, Weilu; Li, Xinwei; Bamba, Motoaki; Kono, Junichiro

2018-06-01

Non-perturbative coupling of photons and excitons produces hybrid particles, exciton-polaritons, which have exhibited a variety of many-body phenomena in various microcavity systems. However, the vacuum Rabi splitting (VRS), which defines the strength of photon-exciton coupling, is usually a single constant for a given system. Here, we have developed a unique architecture in which excitons in an aligned single-chirality carbon nanotube film interact with cavity photons in polarization-dependent manners. The system reveals ultrastrong coupling (VRS up to 329 meV or a coupling-strength-to-transition-energy ratio of 13.3%) for polarization parallel to the nanotube axis, whereas VRS is absent for perpendicular polarization. Between these two extremes, VRS is continuously tunable through polarization rotation with exceptional points separating crossing and anticrossing. The points between exceptional points form equienergy arcs onto which the upper and lower polaritons coalesce. The demonstrated on-demand ultrastrong coupling provides ways to explore topological properties of polaritons and quantum technology applications.

Transition state-finding strategies for use with the growing string method.

PubMed

Goodrow, Anthony; Bell, Alexis T; Head-Gordon, Martin

2009-06-28

Efficient identification of transition states is important for understanding reaction mechanisms. Most transition state search algorithms require long computational times and a good estimate of the transition state structure in order to converge, particularly for complex reaction systems. The growing string method (GSM) [B. Peters et al., J. Chem. Phys. 120, 7877 (2004)] does not require an initial guess of the transition state; however, the calculation is still computationally intensive due to repeated calls to the quantum mechanics code. Recent modifications to the GSM [A. Goodrow et al., J. Chem. Phys. 129, 174109 (2008)] have reduced the total computational time for converging to a transition state by a factor of 2 to 3. In this work, three transition state-finding strategies have been developed to complement the speedup of the modified-GSM: (1) a hybrid strategy, (2) an energy-weighted strategy, and (3) a substring strategy. The hybrid strategy initiates the string calculation at a low level of theory (HF/STO-3G), which is then refined at a higher level of theory (B3LYP/6-31G(*)). The energy-weighted strategy spaces points along the reaction pathway based on the energy at those points, leading to a higher density of points where the energy is highest and finer resolution of the transition state. The substring strategy is similar to the hybrid strategy, but only a portion of the low-level string is refined using a higher level of theory. These three strategies have been used with the modified-GSM and are compared in three reactions: alanine dipeptide isomerization, H-abstraction in methanol oxidation on VO(x)/SiO(2) catalysts, and C-H bond activation in the oxidative carbonylation of toluene to p-toluic acid on Rh(CO)(2)(TFA)(3) catalysts. In each of these examples, the substring strategy was proved most effective by obtaining a better estimate of the transition state structure and reducing the total computational time by a factor of 2 to 3 compared to the modified-GSM. The applicability of the substring strategy has been extended to three additional examples: cyclopropane rearrangement to propylene, isomerization of methylcyclopropane to four different stereoisomers, and the bimolecular Diels-Alder condensation of 1,3-butadiene and ethylene to cyclohexene. Thus, the substring strategy used in combination with the modified-GSM has been demonstrated to be an efficient transition state-finding strategy for a wide range of types of reactions.

Communication: phase transitions, criticality, and three-phase coexistence in constrained cell models.

PubMed

Nayhouse, Michael; Kwon, Joseph Sang-Il; Orkoulas, G

2012-05-28

In simulation studies of fluid-solid transitions, the solid phase is usually modeled as a constrained system in which each particle is confined to move in a single Wigner-Seitz cell. The constrained cell model has been used in the determination of fluid-solid coexistence via thermodynamic integration and other techniques. In the present work, the phase diagram of such a constrained system of Lennard-Jones particles is determined from constant-pressure simulations. The pressure-density isotherms exhibit inflection points which are interpreted as the mechanical stability limit of the solid phase. The phase diagram of the constrained system contains a critical and a triple point. The temperature and pressure at the critical and the triple point are both higher than those of the unconstrained system due to the reduction in the entropy caused by the single occupancy constraint.

Fixed points, stable manifolds, weather regimes, and their predictability

DOE PAGES

Deremble, Bruno; D'Andrea, Fabio; Ghil, Michael

2009-10-27

In a simple, one-layer atmospheric model, we study the links between low-frequency variability and the model’s fixed points in phase space. The model dynamics is characterized by the coexistence of multiple ''weather regimes.'' To investigate the transitions from one regime to another, we focus on the identification of stable manifolds associated with fixed points. We show that these manifolds act as separatrices between regimes. We track each manifold by making use of two local predictability measures arising from the meteorological applications of nonlinear dynamics, namely, ''bred vectors'' and singular vectors. These results are then verified in the framework of ensemblemore » forecasts issued from clouds (ensembles) of initial states. The divergence of the trajectories allows us to establish the connections between zones of low predictability, the geometry of the stable manifolds, and transitions between regimes.« less

Investigation of indirect excitons in bulk 2H-MoS2 using transmission electron energy-loss spectroscopy

NASA Astrophysics Data System (ADS)

Habenicht, Carsten; Schuster, Roman; Knupfer, Martin; Büchner, Bernd

2018-05-01

We have investigated indirect excitons in bulk 2H-MoS2 using transmission electron energy-loss spectroscopy. The electron energy-loss spectra were measured for various momentum transfer values parallel to the and directions of the Brillouin zone. The results allowed the identification of the indirect excitons between the valence band K v and conduction band Λc points, the Γv and K c points as well as adjacent K v and points. The energy-momentum dispersions for the K v-Λc, Γv-K c and K v1- excitons along the line are presented. The former two transitions exhibit a quadratic dispersion which allowed calculating their effective exciton masses based on the effective mass approximation. The K v1- transition follows a more linear dispersion relationship.

Fixed points, stable manifolds, weather regimes, and their predictability.

PubMed

Deremble, Bruno; D'Andrea, Fabio; Ghil, Michael

2009-12-01

In a simple, one-layer atmospheric model, we study the links between low-frequency variability and the model's fixed points in phase space. The model dynamics is characterized by the coexistence of multiple "weather regimes." To investigate the transitions from one regime to another, we focus on the identification of stable manifolds associated with fixed points. We show that these manifolds act as separatrices between regimes. We track each manifold by making use of two local predictability measures arising from the meteorological applications of nonlinear dynamics, namely, "bred vectors" and singular vectors. These results are then verified in the framework of ensemble forecasts issued from "clouds" (ensembles) of initial states. The divergence of the trajectories allows us to establish the connections between zones of low predictability, the geometry of the stable manifolds, and transitions between regimes.

Non-linear thermal evolution of the crystal structure and phase transitions of LaFeO{sub 3} investigated by high temperature X-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Selbach, Sverre M.; Tolchard, Julian R.; Fossdal, Anita

2012-12-15

The crystal structure, anisotropic thermal expansion and structural phase transition of the perovskite LaFeO{sub 3} has been studied by high-temperature X-ray diffraction from room temperature to 1533 K. The structural evolution of the orthorhombic phase with space group Pbnm and the rhombohedral phase with R3{sup Macron }c structure of LaFeO{sub 3} is reported in terms of lattice parameters, thermal expansion coefficients, atomic positions, octahedral rotations and polyhedral volumes. Non-linear lattice expansion across the antiferromagnetic to paramagnetic transition of LaFeO{sub 3} at T{sub N}=735 K was compared to the corresponding behavior of the ferroelectric antiferromagnet BiFeO{sub 3} to gain insight tomore » the magnetoelectric coupling in BiFeO{sub 3}, which is also multiferroic. The first order phase transition of LaFeO{sub 3} from Pbnm to R3{sup Macron }c was observed at 1228{+-}9 K, and a subsequent transition to Pm3{sup Macron }m was extrapolated to occur at 2140{+-}30 K. The stability of the Pbnm and R3{sup Macron }c polymorphs of LaFeO{sub 3} is discussed in terms of the competing enthalpy and entropy of the two crystal polymorphs and the thermal evolution of the polyhedral volume ratio V{sub A}/V{sub B}. - Graphical abstract: Aniostropic thermal evolution of the lattice parameters and phase transition of LaFeO{sub 3}. Highlights: Black-Right-Pointing-Pointer The crystal structure of LaFeO{sub 3} is studied by HTXRD from RT to 1533 K. Black-Right-Pointing-Pointer A non-linear expansion across the Neel temperature is observed for LaFeO{sub 3}. Black-Right-Pointing-Pointer The ratio V{sub A}/V{sub B} is used to rationalize the thermal evolution of the structure.« less

Microgravity Studies of Liquid-Liquid Phase Transitions in Alumina-Yttria Melts

NASA Technical Reports Server (NTRS)

Guynes, Buddy (Technical Monitor); Weber, Richard; Nordine, Paul

2004-01-01

The scientific objective of this research is to increase the fundamental knowledge base for liquid- phase processing of technologically important oxide materials. The experimental objective is to define conditions and hardware requirements for microgravity flight experiments to test and expand the experimental hypotheses that: 1. Liquid phase transitions can occur in undercooled melts by a diffusionless process. 2. Onset of the liquid phase transition is accompanied by a large change in the temperature dependence of melt viscosity. Experiments on undercooled YAG (Y3A15012)- and rare earth oxide aluminate composition liquids demonstrated a large departure from an Arrhenian temperature dependence of viscosity. Liquid YAG is nearly inviscid at its 2240 K melting point. Glass fibers were pulled from melts undercooled by ca. 600 K indicating that the viscosity is on the order of 100 Pans (1000 Poise) at 1600 K. This value of viscosity is 500 times greater than that obtained by extrapolation of data for temperatures above the melting point of YAG. These results show that the liquids are extremely fragile and that the onset of the highly non-Arrhenian viscosity-temperature relationship occurs at a temperature considerably below the equilibrium melting point of the solid phases. Further results on undercooled alumina-yttria melts containing 23-42 mole % yttrium oxide indicate that a congruent liquid-liquid phase transition occurs in the undercooled liquids. The rates of transition are inconsistent with a diffusion-limited process. This research is directed to investigation of the scientifically interesting phenomena of polyamorphism and fragility in undercooled rare earth oxide aluminum oxide liquids. The results bear on the technologically important problem of producing high value rare earth-based optical materials.

Influence of the Cavity Length on the Behavior of Hybrid Fixed-Point Cells Constructed at INRIM

NASA Astrophysics Data System (ADS)

Battuello, M.; Girard, F.; Florio, M.

2015-03-01

Hybrid cells with double carbon/carbon sheets are used at the Istituto Nazionale di Ricerca Metrologica (INRIM) for the realization of both pure metal fixed points and high-temperature metal-carbon eutectic points. Cells for the Cu and Co-C fixed points have been prepared to be used in the high-temperature fixed-point project of the Comité Consultatif de Thermométrie. The results of the evaluation processes were not completely satisfactory for the INRIM cells because of their low transition temperatures with respect to the best cells, and of a rather large melting range for the Co-C cell. A new design of the cells was devised, and considerable improvements were achieved with respect to the transition temperature, and the plateau shape and duration. As for the Cu point, the duration of the freezing plateaux increased by more than 50 % and the freezing temperature increased by 18 mK. As for the Co-C point, the melting temperature, expressed in terms of the point of inflection of the melting curve, increased by about 70 mK. The melting range of the plateaux, expressed as a difference was reduced from about 180 mK to about 130 mK, with melting times increased by about 50 %, as a consequence of an improvement of flatness and run-off of the plateaux.

Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point.

PubMed

Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A

2017-05-09

Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin [Formula: see text] itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting [Formula: see text] enclosing the nematic quantum critical point. For temperatures above [Formula: see text], we see strikingly non-Fermi liquid behavior, including a "nodal-antinodal dichotomy" reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with "bad metal" phenomenology.

A simple mechanical system mimicking phase transitions in a one-dimensional medium

NASA Astrophysics Data System (ADS)

Charru, François

1997-11-01

We study a simple mechanical oscillator the bifurcations of which illustrate first- and second-order phase transitions. The phase diagram of the oscillator exhibits a coexistence curve. This curve ends at a critical point, where three critical exponents can be defined. A metronome may be used to illustrate the main results. We then consider a linear array of such oscillators with elastic coupling, which is governed by the damped Klein - Gordon equation. The classical solutions of this equation, such as fronts propagating in an unstable or in a metastable state, can be guessed at and discussed from the point of view of a mechanical model.

Temperature-dependent dielectric functions and interband critical points of sulfur-rich TlIn(S1-xSex)2 layered solid solution crystals

NASA Astrophysics Data System (ADS)

Gomonnai, O. O.; Gordan, O.; Guranich, P. P.; Slivka, A. G.; Gomonnai, A. V.; Zahn, D. R. T.

2017-12-01

Real and imaginary parts of the dielectric function of TlIn(S1-xSex)2 (x = 0.05, 0.08, 0.25) single crystals were determined in the spectral range from 1 to 5 eV within a temperature interval 140-293 K from spectroscopic ellipsometry measurements. The energies of interband transitions (critical points) of the TlIn(S1-xSex)2 crystals were obtained from the second derivative of the real and imaginary parts of dielectric function. Structural phase transitions are behind the observed change of electronic band structure.

Phase Diagram of Planar Matrix Quantum Mechanics, Tensor, and Sachdev-Ye-Kitaev Models.

PubMed

Azeyanagi, Tatsuo; Ferrari, Frank; Massolo, Fidel I Schaposnik

2018-02-09

We study the Schwinger-Dyson equations of a fermionic planar matrix quantum mechanics [or tensor and Sachdev-Ye-Kitaev (SYK) models] at leading melonic order. We find two solutions describing a high entropy, SYK black-hole-like phase and a low entropy one with trivial IR behavior. There is a line of first order phase transitions that terminates at a new critical point. Critical exponents are nonmean field and differ on the two sides of the transition. Interesting phenomena are also found in unstable and stable bosonic models, including Kazakov critical points and inconsistency of SYK-like solutions of the IR limit.

Phenomenological analysis of thermal hysteresis in Ni-Mn-Ga Heusler alloys

NASA Astrophysics Data System (ADS)

Zagrebin, M. A.; Sokolovskiy, V. V.; Buchelnikov, V. D.

2018-05-01

The manipulation of thermal hysteresis in Ni-Mn-Ga Heusler alloys with coupled magnetostructural phase transition is studied theoretically using the Landau theory, including magnetic, elastic and crystal lattice modulation order parameters as well as an external magnetic field. It is shown that for the assigned combination of phenomenological parameters, in the phase diagrams, the Austenite-Martensite first-order phase transition has a finite (critical) point in which the thermal hysteresis is disappeared. Moreover, this point depends on the relation between modulation and elastic constants as well as on the magnetic field. Obtained results have been compared with other theoretical end experimental data.

The substantive theory of surviving on the margin of a profession.

PubMed

Etowa, Josephine B; Sethi, Sarla; Thompson-Isherwood, Roxie

2009-04-01

Using the grounded theory method, a substantive theory of surviving on the margin of a profession emerged as the core variable that explains the patterns of behavior of black nurses in Canada. Data were collected through audiotaped in-depth interviews of 20 black nurses. The three phases of this theory are realizing, surviving, and thriving and the three critical transitions points are the center, the margin, and the proving ground. The phases and transitions points, as well as the conditions that influence variations in the theory are the focus of this paper. These conditions include racism, diversity, and worklife issues such as healthy workplaces.

Quantifying Complexity in Quantum Phase Transitions via Mutual Information Complex Networks

NASA Astrophysics Data System (ADS)

Valdez, Marc Andrew; Jaschke, Daniel; Vargas, David L.; Carr, Lincoln D.

2017-12-01

We quantify the emergent complexity of quantum states near quantum critical points on regular 1D lattices, via complex network measures based on quantum mutual information as the adjacency matrix, in direct analogy to quantifying the complexity of electroencephalogram or functional magnetic resonance imaging measurements of the brain. Using matrix product state methods, we show that network density, clustering, disparity, and Pearson's correlation obtain the critical point for both quantum Ising and Bose-Hubbard models to a high degree of accuracy in finite-size scaling for three classes of quantum phase transitions, Z2, mean field superfluid to Mott insulator, and a Berzinskii-Kosterlitz-Thouless crossover.

High accuracy heat capacity measurements through the lambda transition of helium with very high temperature resolution

NASA Technical Reports Server (NTRS)

Fairbanks, W. M.; Lipa, J. A.

1984-01-01

A measurement of the heat capacity singularity of helium at the lambda transition was performed with the aim of improving tests of the Renormalization Group (RG) predictions for the static thermodynamic behavior near the singularity. The goal was to approach as closely as possible to the lambda-point while making heat capacity measurements of high accuracy. To do this, a new temperature sensor capable of unprecedented resolution near the lambda-point, and two thermal control systems were used. A short description of the theoretical background and motivation is given. The initial apparatus and results are also described.

Observable consequences of zero-point energy

NASA Astrophysics Data System (ADS)

Sen, Siddhartha; Gupta, Kumar S.

2017-12-01

Spectral line widths, the Lamb shift and the Casimir effect are generally accepted to be observable consequences of the zero-point electromagnetic (ZPEM) fields. A new class of observable consequences of ZPEM field at the mesoscopic scale were recently proposed and observed. Here, we extend this class of observable effects and predict that mesoscopic water layers should have a high value for its solid-liquid phase transition temperature, as illustrated by water inside a single-walled carbon nanotube (CNT). For this case, our analysis predicts that the phase transition temperature scales inversely with the square of the effective radius available for the water flow within the CNT.

VizieR Online Data Catalog: Corot photometry of TYC 455-791-1 (Strassmeier+, 2017)

NASA Astrophysics Data System (ADS)

Strassmeier, K. G.; Granzer, T.; Mallonn, M.; Weber, M.; Weingrill, J.

2016-11-01

From the original CoRoT white-light flux obtained on two consecutive runs, we filter out obvious outliers from the SAA (south Atlantic Anomaly). The third column are the remaining CoRoT data points. The two data set were merged using individual zero-points of 716386.54e- for the first data set and 721882.56e- for the second data set, respectively. The magnitudes thus calculates are in column four. The last column is the combined model of the transit plus a 12th order Fourier-series fit to the out-of-transit data. (1 data file).

Luminosity limits for liquid argon calorimetry

NASA Astrophysics Data System (ADS)

J, Rutherfoord; B, Walker R.

2012-12-01

We have irradiated liquid argon ionization chambers with betas using high-activity Strontium-90 sources. The radiation environment is comparable to that in the liquid argon calorimeters which are part of the ATLAS detector installed at CERN's Large Hadron Collider. We measure the ionization current over a wide range of applied potential for two different source activities and for three different chamber gaps. These studies provide operating experience at exceptionally high ionization rates. We can operate these chambers either in the normal mode or in the space-charge limited regime and thereby determine the transition point between the two. From the transition point we indirectly extract the positive argon ion mobility.

Detection limit for rate fluctuations in inhomogeneous Poisson processes

NASA Astrophysics Data System (ADS)

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Detection limit for rate fluctuations in inhomogeneous Poisson processes.

PubMed

Shintani, Toshiaki; Shinomoto, Shigeru

2012-04-01

Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

Multiple buoyancy driven flows in a vertical cylinder heated from below

NASA Technical Reports Server (NTRS)

Yamaguchi, Y.; Chang, C. J.; Brown, R. A.

1983-01-01

The structure of axisymmetric buoyancy-driven convection in a vertical cylinder heated from below is probed by finite element solution of the Boussinesq equations coupled with computed-implemented perturbation techniques for detecting and tracking multiple flows and for determining flow stability. Results are reported for fluids with Prandtl number of one and for cylinders with aspect ratio (Lambda) (defined as the height to radius of the cylinder) between 0.5 and 2.25. Extensive calculations of the neutral stability curve for the static solution and of the nonlinear motions along the bifurcating flow families show a continuous evolution of the primary cellular motion from a single toroidal cell to two and three cells nested radially in the cylinder, instead of the sharp transitions found for a cylinder with shear-free sidewalls. The smooth transitions in flow structure with Rayleigh number and lambda are explained by nonlinear connectivity between the first two bifurcating flow families formed either by a secondary bifurcation point for Lambda or = Lambda * approximately 0.80 or by a limit point for Lambda Lambda *. The transition between these two modes may be described by the theory of multiple limit point bifurcation.

Tricritical points in a Vicsek model of self-propelled particles with bounded confidence

NASA Astrophysics Data System (ADS)

Romensky, Maksym; Lobaskin, Vladimir; Ihle, Thomas

2014-12-01

We study the orientational ordering in systems of self-propelled particles with selective interactions. To introduce the selectivity we augment the standard Vicsek model with a bounded-confidence collision rule: a given particle only aligns to neighbors who have directions quite similar to its own. Neighbors whose directions deviate more than a fixed restriction angle α are ignored. The collective dynamics of this system is studied by agent-based simulations and kinetic mean-field theory. We demonstrate that the reduction of the restriction angle leads to a critical noise amplitude decreasing monotonically with that angle, turning into a power law with exponent 3/2 for small angles. Moreover, for small system sizes we show that upon decreasing the restriction angle, the kind of the transition to polar collective motion changes from continuous to discontinuous. Thus, an apparent tricritical point with different scaling laws is identified and calculated analytically. We investigate the shifting and vanishing of this point due to the formation of density bands as the system size is increased. Agent-based simulations in small systems with large particle velocities show excellent agreement with the kinetic theory predictions. We also find that at very small interaction angles, the polar ordered phase becomes unstable with respect to the apolar phase. We derive analytical expressions for the dependence of the threshold noise on the restriction angle. We show that the mean-field kinetic theory also permits stationary nematic states below a restriction angle of 0.681 π . We calculate the critical noise, at which the disordered state bifurcates to a nematic state, and find that it is always smaller than the threshold noise for the transition from disorder to polar order. The disordered-nematic transition features two tricritical points: At low and high restriction angle, the transition is discontinuous but continuous at intermediate α . We generalize our results to systems that show fragmentation into more than two groups and obtain scaling laws for the transition lines and the corresponding tricritical points. A numerical method to evaluate the nonlinear Fredholm integral equation for the stationary distribution function is also presented. This method is shown to give excellent agreement with agent-based simulations, even in strongly ordered systems at noise values close to zero.

Lattice crossover and phase transitions in NdAlO{sub 3}-GdAlO{sub 3} system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasylechko, L., E-mail: crystal-lov@polynet.lviv.ua; Shmanko, H.; Ohon, N.

2013-02-15

Phase and structural behaviour in the (1-x)NdAlO{sub 3}-xGdAlO{sub 3} system in a whole concentration range has been studied by means of in situ high-resolution X-ray synchrotron powder diffraction technique and differential thermal analysis. Two kinds of solid solutions Nd{sub 1-x}Gd{sub x}AlO{sub 3} have been found at room temperature: one with rhombohedral (x<0.15) and one with orthorhombic (x{>=}0.20) symmetry. A morphotropic phase transition occurs at x Almost-Equal-To 0.15, where the co-existence of both phases was observed. Peculiarity of the orthorhombic solid solution is the lattice parameter crossover at the compositions with x=0.33, 0.49 and 0.62. First-order structural transition Pbnm{r_reversible}R3{sup Macron }cmore » has been detected both from in situ powder diffraction and thermal analysis data. Continuous phase transformation R3{sup Macron }c{r_reversible}Pm3{sup Macron }m above 2140 K has been predicted for Nd-rich sample Nd{sub 0.85}Gd{sub 0.15}AlO{sub 3} from the extrapolation of high-temperature behaviour of the lattice parameter ratio of the rhombohedral phase. Based on the experimental data, the phase diagram of the pseudo-binary system NdAlO{sub 3}-GdAlO{sub 3} has been constructed. - Graphical abstract: Concentration dependencies of normalized lattice parameters of Nd{sub 1-x}Gd{sub x}AlO{sub 3} perovskite solid solutions. Highlights: Black-Right-Pointing-Pointer Two kinds of solid solutions Nd{sub 1-x}Gd{sub x}AlO{sub 3} were found in the NdAlO{sub 3}-GdAlO{sub 3} system. Black-Right-Pointing-Pointer Morphotropic transition between both perovskite phases occurs at x Almost-Equal-To 0.15. Black-Right-Pointing-Pointer Lattice parameter crossover was found in orthorhombic solid solution. Black-Right-Pointing-Pointer Temperature driven first-order phase transition Pbnm{r_reversible}R3{sup Macron }c was found in Nd{sub 1-x}Gd{sub x}AlO{sub 3}. Black-Right-Pointing-Pointer Phase diagram of the pseudo-binary system NdAlO{sub 3}-GdAlO{sub 3} has been constructed.« less

Molecular dynamics study of intermediate phase of long chain alkyl sulfonate/water systems.

PubMed

Poghosyan, Armen H; Arsenyan, Levon H; Shahinyan, Aram A

2013-01-08

Using atomic level simulation we aimed to investigate various intermediate phases of the long chain alkyl sulfonate/water system. Overall, about 800 ns parallel molecular dynamics simulation study was conducted for a surfactant/water system consisting of 128 sodium pentadecyl sulfonate and 2251 water molecules. The GROMACS software code with united atom force field was applied. Despite some differences, the analysis of main structural parameters is in agreement with X-ray experimental findings. The mechanism of self-assembly of SPDS molecules was also examined. At T = 323 K we obtained both tilted fully interdigitated and liquid crystalline-like disordered hydrocarbon chains; hence, the presence of either gel phase that coexists with a lamellar phase or metastable gel phase with fraction of gauche configuration can be assumed. Further increase of temperature revealed that the system underwent a transition to a lamellar phase, which was clearly identified by the presence of fully disordered hydrocarbon chains. The transition from gel-to-fluid phase was implemented by simulated annealing treatment, and the phase transition point at T = 335 K was identified. The surfactant force field in its presented set is surely enabled to fully demonstrate the mechanism of self-assembly and the behavior of phase transition making it possible to get important information around the phase transition point.

Electronic structure and quantum spin fluctuations at the magnetic phase transition in MnSi

NASA Astrophysics Data System (ADS)

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

2018-05-01

The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions.

Pressure-induced topological insulator-to-metal transition and superconductivity in Sn-doped B i1.1S b0.9T e2S

NASA Astrophysics Data System (ADS)

An, Chao; Chen, Xuliang; Wu, Bin; Zhou, Yonghui; Zhou, Ying; Zhang, Ranran; Park, Changyong; Song, Fengqi; Yang, Zhaorong

2018-05-01

Tetradymite-type topological insulator Sn-doped B i1.1S b0.9T e2S (Sn-BSTS), with a surface state Dirac point energy well isolated from the bulk valence and conduction bands, is an ideal platform for studying the topological transport phenomena. Here, we present high-pressure transport studies on single-crystal Sn-BSTS, combined with Raman scattering and synchrotron x-ray diffraction measurements. Over the studied pressure range of 0.7-37.2 GPa, three critical pressure points can be observed: (i) At ˜9 GPa, a pressure-induced topological insulator-to-metal transition is revealed due to closure of the bulk band gap, which is accompanied by changes in slope of the Raman frequencies and a minimum in c /a within the pristine rhombohedral structure (R -3 m ); (ii) at ˜13 GPa, superconductivity is observed to emerge, along with the R -3 m to a C 2 /c (monoclinic) structural transition; (iii) at ˜24 GPa, the superconducting transition onset temperature TC reaches a maximum of ˜12 K , accompanied by a second structural transition from the C 2 /c to a body-centered cubic I m -3 m phase.

Proton-neutron sdg boson model and spherical-deformed phase transition

NASA Astrophysics Data System (ADS)

Otsuka, Takaharu; Sugita, Michiaki

1988-12-01

The spherical-deformed phase transition in nuclei is described in terms of the proton-neutron sdg interacting boson model. The sdg hamiltonian is introduced to model the pairing+quadrupole interaction. The phase transition is reproduced in this framework as a function of the boson number in the Sm isotopes, while all parameters in the hamiltonian are kept constant at values reasonable from the shell-model point of view. The sd IBM is derived from this model through the renormalization of g-boson effects.

Transition within a Hypervelocity Boundary Layer on a 5-degree Half-Angle Cone in Freestream Air/CO2 Mixtures

DTIC Science & Technology

2013-01-01

Pasadena, CA, 91125 Nomenclature A = amplitude of oscillation f = frequency hres = reservoir enthalpy Me = boundary layer edge Mach number Pres...showed an increase in the reference Reynolds number Re* at the point of transition as reservoir enthalpy hres increased. Germain and Adam also observed...that flows of CO2 transitioned at higher values of Re* than flows of air for the same hres and Pres. Johnson et al. (1998) studied this effect with a

Study on Ultrafast Photodynamics of Novel Multilayered Thin Films for Device Applications

DTIC Science & Technology

2004-07-31

study ultrafast phase-transition of VO2 thin film. This part of work was started right after the new laser installed. With better laser output...1-3]. With the purpose of combined effect that the proposed ultrafast phase-transition VO2 thin film deposited on a substrate of heavy metal...second point of focus was to study ultrafast phase-transition of VO2 thin film. This part of work was started right after the new laser installed

Glass Transition Temperature Measurement for Undercured Cyanate Ester Networks: Challenges, Tips, and Tricks (Briefing Charts)

DTIC Science & Technology

2014-01-29

DISTRIBUTION A: Approved for public release; distribution is unlimited. Thermosetting Polymers Have a TG Envelope – Not Just a TG 4 • The glass transition...glass transition temperature of a thermosetting polymer can vary over a wide range of temperatures depending on how the polymer is processed • A... thermosetting polymer with only one kind of network formation and negligible side reactions, the conversion may be determined at every point in the scan. • By

Chemical potential driven phase transition of black holes in anti-de Sitter space

NASA Astrophysics Data System (ADS)

Galante, Mario; Giribet, Gaston; Goya, Andrés; Oliva, Julio

2015-11-01

Einstein-Maxwell theory conformally coupled to a scalar field in D dimensions may exhibit a phase transition at low temperature whose end point is an asymptotically anti-de Sitter black hole with a scalar field profile that is regular everywhere outside and on the horizon. This provides a tractable model to study the phase transition of hairy black holes in anti-de Sitter space in which the backreaction on the geometry can be solved analytically.

News and views in discontinuous phase transitions

NASA Astrophysics Data System (ADS)

Nagler, Jan

2014-03-01

Recent progress in the theory of discontinuous percolation allow us to better understand the the sudden emergence of large-scale connectedness both in networked systems and on the lattice. We analytically study mechanisms for the amplification of critical fluctuations at the phase transition point, non-self-averaging and power law fluctuations. A single event analysis allow to establish criteria for discontinuous percolation transitions, even on the high-dimensional lattice. Some applications such as salad bowl percolation, and inverse fragmentation are discussed.

Longitudinal Prediction of Quality-of-Life Scores and Locomotion in Individuals With Traumatic Spinal Cord Injury.

PubMed

Hiremath, Shivayogi V; Hogaboom, Nathan S; Roscher, Melissa R; Worobey, Lynn A; Oyster, Michelle L; Boninger, Michael L

2017-12-01

To examine (1) differences in quality-of-life scores for groups based on transitions in locomotion status at 1, 5, and 10 years postdischarge in a sample of people with spinal cord injury (SCI); and (2) whether demographic factors and transitions in locomotion status can predict quality-of-life measures at these time points. Retrospective case study of the National SCI Database. Model SCI Systems Centers. Individuals with SCI (N=10,190) from 21 SCI Model Systems Centers, identified through the National SCI Model Systems Centers database between the years 1985 and 2012. Subjects had FIM (locomotion mode) data at discharge and at least 1 of the following: 1, 5, or 10 years postdischarge. Not applicable. FIM-locomotion mode; Severity of Depression Scale; Satisfaction With Life Scale; and Craig Handicap Assessment and Reporting Technique. Participants who transitioned from ambulation to wheelchair use reported lower participation and life satisfaction, and higher depression levels (P<.05) than those who maintained their ambulatory status. Participants who transitioned from ambulation to wheelchair use reported higher depression levels (P<.05) and no difference for participation (P>.05) or life satisfaction (P>.05) compared with those who transitioned from wheelchair to ambulation. Demographic factors and locomotion transitions predicted quality-of-life scores at all time points (P<.05). The results of this study indicate that transitioning from ambulation to wheelchair use can negatively impact psychosocial health 10 years after SCI. Clinicians should be aware of this when deciding on ambulation training. Further work to characterize who may be at risk for these transitions is needed. Copyright © 2017 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

What causes the Besnus transition in monoclinic pyrrhotite?

NASA Astrophysics Data System (ADS)

Gehring, A. U.; Koulialias, D.; Löffler, J. F.; Charilaou, M.

2016-12-01

Monoclinic 4C pyrrhotite (ideal formula Fe7S8) is a major magnetic remanence carrier in the Earth's crust and in extraterrestrial materials. Because of its low-temperature magnetic transition around 30 K also known as Besnus transition, this mineral phase is easily detectable in rock samples. An intrinsic origin of the Besnus transition due to a crystallographic change similar to that in the Verwey transition has generally been postulated (1). Although the physical properties of pyrrhotite have intensively been studied, the physics behind the pronounced change in magnetization at the low-temperature transition is still unresolved. To address this question we performed structural and magnetic analyses on a natural pyrrhotite single crystal (Fe6.6S8) from Auerbach, Germany (2,3). Chemical analysis, X-ray diffractometry and transmission electron microscopy show that this pyrrhotite consists of an intergrowth of 4C and an incommensurate 5C* superstructure that are polymorphs with different vacancy distributions. The occurrence of two superstructures is magnetically confirmed by symmetric inflection points in the hysteresis measurements above the transition at about 30 K. The disappearance of the inflection points and the associated change of the hysteresis parameters indicate that the two superstructures become embedded to form a unitary magnetic anisotropy system at the transition. This embedding of the 5C* into the 4C pyrrhotite at about 30 K is directly visible by the occurrence of additional 4-fold and 12-fold symmetry terms in magnetic anisotropy and anisotropic magnetic resistivity mesarurements, respectively. From this it follows that the Besnus transition in monoclinic pyrrhotite is an extrinsic magnetic phenomenon with respect to the 4C superstructure, i.e., a coupling effect, and therefore the physics behind it is in fact different from that of the well-known Verwey transition. (1) Rochette et al., The IRM Quarterly, 21, 1 (2011); (2) Charilaou et al., J. Appl. Phys., 118, 083903 (2015); (3) Koulialias et al., Geophys. J. Int., 204, 961-967 (2016).

Detecting critical state before phase transition of complex systems by hidden Markov model

NASA Astrophysics Data System (ADS)

Liu, Rui; Chen, Pei; Li, Yongjun; Chen, Luonan

Identifying the critical state or pre-transition state just before the occurrence of a phase transition is a challenging task, because the state of the system may show little apparent change before this critical transition during the gradual parameter variations. Such dynamics of phase transition is generally composed of three stages, i.e., before-transition state, pre-transition state, and after-transition state, which can be considered as three different Markov processes. Thus, based on this dynamical feature, we present a novel computational method, i.e., hidden Markov model (HMM), to detect the switching point of the two Markov processes from the before-transition state (a stationary Markov process) to the pre-transition state (a time-varying Markov process), thereby identifying the pre-transition state or early-warning signals of the phase transition. To validate the effectiveness, we apply this method to detect the signals of the imminent phase transitions of complex systems based on the simulated datasets, and further identify the pre-transition states as well as their critical modules for three real datasets, i.e., the acute lung injury triggered by phosgene inhalation, MCF-7 human breast cancer caused by heregulin, and HCV-induced dysplasia and hepatocellular carcinoma.

A novel method for vaginal cylinder treatment planning: a seamless transition to 3D brachytherapy

PubMed Central

Wu, Vincent; Wang, Zhou; Patil, Sachin

2012-01-01

Purpose Standard treatment plan libraries are often used to ensure a quick turn-around time for vaginal cylinder treatments. Recently there is increasing interest in transitioning from conventional 2D radiograph based brachytherapy to 3D image based brachytherapy, which has resulted in a substantial increase in treatment planning time and decrease in patient through-put. We describe a novel technique that significantly reduces the treatment planning time for CT-based vaginal cylinder brachytherapy. Material and methods Oncentra MasterPlan TPS allows multiple sets of data points to be classified as applicator points which has been harnessed in this method. The method relies on two hard anchor points: the first dwell position in a catheter and an applicator configuration specific dwell position as the plan origin and a soft anchor point beyond the last active dwell position to define the axis of the catheter. The spatial location of various data points on the applicator's surface and at 5 mm depth are stored in an Excel file that can easily be transferred into a patient CT data set using window operations and then used for treatment planning. The remainder of the treatment planning process remains unaffected. Results The treatment plans generated on the Oncentra MasterPlan TPS using this novel method yielded results comparable to those generated on the Plato TPS using a standard treatment plan library in terms of treatment times, dwell weights and dwell times for a given optimization method and normalization points. Less than 2% difference was noticed between the treatment times generated between both systems. Using the above method, the entire planning process, including CT importing, catheter reconstruction, multiple data point definition, optimization and dose prescription, can be completed in ~5–10 minutes. Conclusion The proposed method allows a smooth and efficient transition to 3D CT based vaginal cylinder brachytherapy planning. PMID:23349650

Global entanglement and quantum phase transitions in the transverse XY Heisenberg chain

NASA Astrophysics Data System (ADS)

Radgohar, Roya; Montakhab, Afshin

2018-01-01

We provide a study of various quantum phase transitions occurring in the XY Heisenberg chain in a transverse magnetic field using the Meyer-Wallach (MW) measure of (global) entanglement. Such a measure, while being readily evaluated, is a multipartite measure of entanglement as opposed to more commonly used bipartite measures. Consequently, we obtain analytic expression of the measure for finite-size systems and show that it can be used to obtain critical exponents via finite-size scaling with great accuracy for the Ising universality class. We also calculate an analytic expression for the isotropic (XX) model and show that global entanglement can precisely identify the level-crossing points. The critical exponent for the isotropic transition is obtained exactly from an analytic expression for global entanglement in the thermodynamic limit. Next, the general behavior of the measure is calculated in the thermodynamic limit considering the important role of symmetries for this limit. The so-called oscillatory transition in the ferromagnetic regime can only be characterized by the thermodynamic limit where global entanglement is shown to be zero on the transition curve. Finally, the anisotropic transition is explored where it is shown that global entanglement exhibits an interesting behavior in the finite-size limit. In the thermodynamic limit, we show that global entanglement shows a cusp singularity across the Ising and anisotropic transition, while showing non-analytic behavior at the XX multicritical point. It is concluded that global entanglement, despite its relative simplicity, can be used to identify all the rich structure of the ground-state Heisenberg chain.

Operator product expansion in Liouville field theory and Seiberg-type transitions in log-correlated random energy models

NASA Astrophysics Data System (ADS)

Cao, Xiangyu; Le Doussal, Pierre; Rosso, Alberto; Santachiara, Raoul

2018-04-01

We study transitions in log-correlated random energy models (logREMs) that are related to the violation of a Seiberg bound in Liouville field theory (LFT): the binding transition and the termination point transition (a.k.a., pre-freezing). By means of LFT-logREM mapping, replica symmetry breaking and traveling-wave equation techniques, we unify both transitions in a two-parameter diagram, which describes the free-energy large deviations of logREMs with a deterministic background log potential, or equivalently, the joint moments of the free energy and Gibbs measure in logREMs without background potential. Under the LFT-logREM mapping, the transitions correspond to the competition of discrete and continuous terms in a four-point correlation function. Our results provide a statistical interpretation of a peculiar nonlocality of the operator product expansion in LFT. The results are rederived by a traveling-wave equation calculation, which shows that the features of LFT responsible for the transitions are reproduced in a simple model of diffusion with absorption. We examine also the problem by a replica symmetry breaking analysis. It complements the previous methods and reveals a rich large deviation structure of the free energy of logREMs with a deterministic background log potential. Many results are verified in the integrable circular logREM, by a replica-Coulomb gas integral approach. The related problem of common length (overlap) distribution is also considered. We provide a traveling-wave equation derivation of the LFT predictions announced in a precedent work.

Thermodynamic model of social influence on two-dimensional square lattice: Case for two features

NASA Astrophysics Data System (ADS)

Genzor, Jozef; Bužek, Vladimír; Gendiar, Andrej

2015-02-01

We propose a thermodynamic multi-state spin model in order to describe equilibrial behavior of a society. Our model is inspired by the Axelrod model used in social network studies. In the framework of the statistical mechanics language, we analyze phase transitions of our model, in which the spin interaction J is interpreted as a mutual communication among individuals forming a society. The thermal fluctuations introduce a noise T into the communication, which suppresses long-range correlations. Below a certain phase transition point Tt, large-scale clusters of the individuals, who share a specific dominant property, are formed. The measure of the cluster sizes is an order parameter after spontaneous symmetry breaking. By means of the Corner transfer matrix renormalization group algorithm, we treat our model in the thermodynamic limit and classify the phase transitions with respect to inherent degrees of freedom. Each individual is chosen to possess two independent features f = 2 and each feature can assume one of q traits (e.g. interests). Hence, each individual is described by q2 degrees of freedom. A single first-order phase transition is detected in our model if q > 2, whereas two distinct continuous phase transitions are found if q = 2 only. Evaluating the free energy, order parameters, specific heat, and the entanglement von Neumann entropy, we classify the phase transitions Tt(q) in detail. The permanent existence of the ordered phase (the large-scale cluster formation with a non-zero order parameter) is conjectured below a non-zero transition point Tt(q) ≈ 0.5 in the asymptotic regime q → ∞.

Point defects in Cu 2 ZnSnSe 4 (CZTSe): Resonant X-ray diffraction study of the low-temperature order/disorder transition: Point defects in Cu 2 ZnSnSe 4 (CZTSe)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schelhas, L. T.; Stone, K. H.; Harvey, S. P.

The interest in Cu2ZnSn(S,Se)4 (CZTS) for photovoltaic applications is motivated by similarities to Cu(In,Ga)Se2 while being comprised of non-toxic and earth abundant elements. However, CZTS suffers from a Voc deficit, where the Voc is much lower than expected based on the band gap, which may be the result of a high concentration of point-defects in the CZTS lattice. Recently, reports have observed a low-temperature order/disorder transition by Raman and optical spectroscopies in CZTS films and is reported to describe the ordering of Cu and Zn atoms in the CZTS crystal structure. To directly determine the level of Cu/Zn ordering, wemore » have used resonant-XRD, a site, and element specific probe of long range order. We used CZTSe films annealed just below and quenched from just above the transition temperature; based on previous work, the Cu and Zn should be ordered and highly disordered, respectively. Our data show that there is some Cu/Zn ordering near the low temperature transition but significantly less than high chemical order expected from Raman. To understand both our resonant-XRD results and the Raman results, we present a structural model that involves antiphase domain boundaries and accommodates the excess Zn within the CZTS lattice.« less

NSSEFF Designing New Higher Temperature Superconductors

DTIC Science & Technology

2017-04-13

electronic structure calculations are integrated with the synthesis of new superconducting materials, with the aim of providing a rigorous test of the...apparent association of high temperature superconductivity with electron delocalization transitions occurring at quantum critical points. We will use...realistic electronic structure calculations to assess which transition metal monopnictides are closest to electron delocalization, and hence optimal for

Where Have All the Teachers Gone: A Case Study in Transitioning

ERIC Educational Resources Information Center

Potgieter, Amanda S.

2016-01-01

This paper reports the autobiographical narrative of Mr. L., as case-in-point example of the thresholding moment and the process of transitioning into Academia. The role of the lecturer-mentor and the multi-logic space that facilitates the process are clarified. I use hermeneutic phenomenology and interpretivism as methodological tools. This ex…

The E-Only Tipping Point for Journals: What's Ahead in the Print-to-Electronic Transition Zone

ERIC Educational Resources Information Center

Johnson, Richard K.; Luther, Judy

2007-01-01

This report examines the issues associated with moves toward electronic-only publication of journals, based on interviews with academic librarians and journal publishers. Noting that publishers and libraries today find themselves in an extended transition zone between print-only and e-only journals, the report investigates forces driving change…

Academic Socialization and the Transition to Elementary School: Parents' Conceptions of School Readiness, Practices, and Children's Academic Achievement Trajectories

ERIC Educational Resources Information Center

Puccioni, Jaime Lynn

2012-01-01

By the time children enter kindergarten, significant socioeconomic and racial gaps in academic achievement exist (Coley, 2002; Rouse, Brooks-Gunn, & Mclanahan, 2005). Kindergarten is considered to be a pivotal point of educational transition, as academic achievement upon kindergarten entry is associated with subsequent academic success…

Students' Writing "In Transition" from A-Levels to University: How Assessment Drives Students' Understandings, Practices and Discourses

ERIC Educational Resources Information Center

Baker, Sally

2017-01-01

The lament that "students can't write" remains loud and defiant, even after years of research pointing to the myriad factors that make students' writing challenging, particularly when they move into university. This paper reports on a longitudinal, ethnographic study which explored students' writing "in transition," from…

A Review of the Approaches Investigating the Post-16 Transition of Young Adults with Learning Difficulties

ERIC Educational Resources Information Center

Carroll, Catherine

2015-01-01

Investigations into the lives and transition from compulsory schooling of young adults with a disability, including a learning difficulty (LD), are increasing. The emerging consensus is one which points to this group of young people experiencing greater difficulties and poorer outcomes compared to the general population. How these investigations…

From Primary to Secondary Science: Keeping the Threads Intact

ERIC Educational Resources Information Center

Mould, Kirsten

2015-01-01

There are many transition points in the school life of a child, but the move from primary to secondary school is a particularly significant one. How can both the social and academic threads remain intact? In this article, Kristen Mould discusses the main issues relating to transition from primary to secondary science. She cites the primary factors…

A Latent Transition Analysis of Academic Intrinsic Motivation from Childhood through Adolescence

ERIC Educational Resources Information Center

Marcoulides, George A.; Gottfried, Adele Eskeles; Gottfried, Allen W.; Oliver, Pamella H.

2008-01-01

A longitudinal modeling approach was utilized to determine the existence of latent classes with regard to academic intrinsic motivation and the points of stability and transition of individuals between and within classes. A special type of latent Markov Chain model using "Mplus" was fit to data from the Fullerton Longitudinal Study, with…

Connecting the Forgotten Half: The School-to-Work Transition of Noncollege-Bound Youth

ERIC Educational Resources Information Center

Ling, Thomson J.; O'Brien, Karen M.

2013-01-01

While previous research has examined the school-to-work transition of noncollege-bound youth, most have considered how a limited set of variables relate to job attainment at a single point in time. This exploratory study extended beyond the identification of constructs associated with obtaining a job to investigate how several factors, collected…

Are Madrean ecosystems approaching tipping points? Anticipating interactions of landscape disturbance and climate change

Treesearch

Donald A. Falk

2013-01-01

Contemporary climate change is driving transitions in many Madrean ecosystems, but the time scale of these changes is accelerated greatly by severe landscape disturbances such as wildfires and insect outbreaks. Landscape-scale disturbance events such as wildfires interact with prior disturbance patterns and landscape structure to catalyze abrupt transitions to novel...

Density Affects the Nature of the Hexatic-Liquid Transition in Two-Dimensional Melting of Soft-Core Systems

NASA Astrophysics Data System (ADS)

Zu, Mengjie; Liu, Jun; Tong, Hua; Xu, Ning

2016-08-01

We find that both continuous and discontinuous hexatic-liquid transitions can happen in the melting of two-dimensional solids of soft-core disks. For three typical model systems, Hertzian, harmonic, and Gaussian-core models, we observe the same scenarios. These systems exhibit reentrant crystallization (melting) with a maximum melting temperature Tm happening at a crossover density ρm. The hexatic-liquid transition at a density smaller than ρm is discontinuous. Liquid and hexatic phases coexist in a density interval, which becomes narrower with increasing temperature and tends to vanish approximately at Tm. Above ρm, the transition is continuous, in agreement with the Kosterlitz-Thouless-Halperin-Nelson-Young theory. For these soft-core systems, the nature of the hexatic-liquid transition depends on density (pressure), with the melting at ρm being a plausible transition point from discontinuous to continuous hexatic-liquid transition.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1985-01-01

A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information. The data were analyzed by using a version of the STAN5 two-dimensional boundary layer code. The transition starting and ending points were determined by adjusting parameters in STAN5 until the calculations matched the data. The results are presented as a table of the deduced transition location and length as functions of the test parameters. The data sets reviewed cover a wide range of flow conditions, from low-speed, flat-plate tests to full-scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free-stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates.

PubMed

Middey, S; Meyers, D; Kareev, M; Cao, Yanwei; Liu, X; Shafer, P; Freeland, J W; Kim, J-W; Ryan, P J; Chakhalian, J

2018-04-13

Coupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO_{3}. Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries.

Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates

NASA Astrophysics Data System (ADS)

Middey, S.; Meyers, D.; Kareev, M.; Cao, Yanwei; Liu, X.; Shafer, P.; Freeland, J. W.; Kim, J.-W.; Ryan, P. J.; Chakhalian, J.

2018-04-01

Coupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO3 . Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries.

Phase transition in the (Li 0.5-( x/2) K 0.5-( x/2) Cs x) 2SO 4 system

NASA Astrophysics Data System (ADS)

Hamed, A. E.; El-Aziz, Y. M. Abd.; Madi, N. K.; Kassem, M. E.

1995-12-01

Phase transition in the (Li 0.5-( x/2) K 0.5-( x/2) Cs x) 2SO 4 system was studied by measuring the specific heat at constant pressure, C p, as a function of temperature in the temperature range 300-800 K. For non-zero values of X ( X = 0.2%, 0.5%, 1% and 2%) the critical behaviour of the phase transition was found to change considerably compared with that of X = 0 or pure LiKSO 4. The observed change in the phase transition with increase of Cs 2SO 4 content ( X) was accompanied by a decrease in the thermodynamic parameters: the value of the specific heat at the transition point (Δ C P) max, the transition temperature, T1, and the value of the energy of ordering. The results were interpreted within the Landau thermodynamic theory of the phase transition.

Transition State Geometry Measurements from 13C Isotope Effects. The Experimental Transition State for the Epoxidation of Alkenes with Oxaziridines

PubMed Central

Hirschi, Jennifer S.; Takeya, Tetsuya; Hang, Chao; Singleton, Daniel A.

2009-01-01

We suggest here and evaluate a methodology for the measurement of specific interatomic distances from a combination of theoretical calculations and experimentally measured 13C kinetic isotope effects. This process takes advantage of a broad diversity of transition structures available for the epoxidation of 2-methyl-2-butene with oxaziridines. From the isotope effects calculated for these transition structures, a theory-independent relationship between the C-O bond distances of the newly forming bonds and the isotope effects is established. Within the precision of the measurement, this relationship in combination with the experimental isotope effects provides a highly accurate picture of the C-O bonds forming at the transition state. The diversity of transition structures also allows an evaluation of the Schramm process for defining transition state geometries based on calculations at non-stationary points, and the methodology is found to be reasonably accurate. PMID:19146405

Determination of Boundary-Layer Transition on Three Symmetrical Airfoils in the NACA Full-Scale Wind Tunnel

NASA Technical Reports Server (NTRS)

Silverstein, Abe; Becker, John V

1938-01-01

For the purpose of studying the transition from laminar to turbulent flow, boundary-layer measurements were made in the NACA full-scale wind tunnel on three symmetrical airfoils of NACA 0009, 0012, and 0018 sections. The effects of variations in lift coefficient, Reynolds number, and airfoil thickness on transition were investigated. Air speed in the boundary layer was measured by total-head tubes and by hot wires; a comparison of transition as indicated by the two techniques was obtained. The results indicate no unique value of Reynolds number for the transition, whether the Reynolds number is based upon the distance along the chord or upon the thickness of the boundary layer at the transition point. In general, the transition is not abrupt and occurs in a region that varies in length as a function of the test conditions.

Genuine non-self-averaging and ultraslow convergence in gelation.

PubMed

Cho, Y S; Mazza, M G; Kahng, B; Nagler, J

2016-08-01

In irreversible aggregation processes droplets or polymers of microscopic size successively coalesce until a large cluster of macroscopic scale forms. This gelation transition is widely believed to be self-averaging, meaning that the order parameter (the relative size of the largest connected cluster) attains well-defined values upon ensemble averaging with no sample-to-sample fluctuations in the thermodynamic limit. Here, we report on anomalous gelation transition types. Depending on the growth rate of the largest clusters, the gelation transition can show very diverse patterns as a function of the control parameter, which includes multiple stochastic discontinuous transitions, genuine non-self-averaging and ultraslow convergence of the transition point. Our framework may be helpful in understanding and controlling gelation.

Sensitivity to perturbations and quantum phase transitions.

PubMed

Wisniacki, D A; Roncaglia, A J

2013-05-01

The local density of states or its Fourier transform, usually called fidelity amplitude, are important measures of quantum irreversibility due to imperfect evolution. In this Rapid Communication we study both quantities in a paradigmatic many body system, the Dicke Hamiltonian, where a single-mode bosonic field interacts with an ensemble of N two-level atoms. This model exhibits a quantum phase transition in the thermodynamic limit, while for finite instances the system undergoes a transition from quasi-integrability to quantum chaotic. We show that the width of the local density of states clearly points out the imprints of the transition from integrability to chaos but no trace remains of the quantum phase transition. The connection with the decay of the fidelity amplitude is also established.

Determining a young dancer's readiness for dancing on pointe.

PubMed

Shah, Selina

2009-01-01

Ballet is one of the most popular youth activities in the United States. Many ballet students eventually train to dance "en pointe," the French words for "on pointe," or "on the tips of their toes." No research exists to define criteria for determining when a young dancer can transition from dancing in ballet slippers to dancing in pointe shoes. However, dancers can be evaluated for this progression based on a number of factors, including adequate foot and ankle plantarflexion, technique, training, proprioception, alignment, and strength.

Extensible 3D (X3D) Graphics for Visualizing Marine Mammal Reaction to Underwater Sound on the Southern California ASW Range (SOAR)

DTIC Science & Technology

2007-06-01

file ARC- 20060811T130816.txt, where color is used to represent points in time (red being the earliest, transitioning to orange, yellow , then white...Administration (NOAA), using passive hydrophone arrays along the mid-Atlantic ridge to listen for underwater earthquakes and volcanoes , have found that a...appeared. The earliest data points were designated red, and later points were shades of orange and yellow , until the last points (relative to the

Thermodynamics and Phase Transition from Regular Bardeen Black Hole Surrounded by Quintessence

NASA Astrophysics Data System (ADS)

Saleh, Mahamat; Thomas, Bouetou Bouetou; Kofane, Timoleon Crepin

2018-05-01

In this paper, thermodynamics and phase transition are investigated for the regular Bardeen black hole surrounded by quintessence. Considering the metric of the Bardeen spacetime surrounded by quintessence, we derived the Unruh-Verlinde temperature. Using the first law of thermodynamics, we derived the expressions of the Hawking temperature as well as the specific heat for the black hole. Explicitly, their behaviors were plotted. It results that the magnetic monopole charge β as well as the presence of quintessence decrease the temperature and induce a thermodynamics phase transition in the spacetime. Moreover, when increasing the density of quintessence, the transition point moves to lower entropies.

Direct Numerical Simulation of a Plane Transitional Wall Jet

NASA Astrophysics Data System (ADS)

Ramesh, O.; Varghese, Joel

2017-11-01

A transitional plane wall jet is studied using direct numerical simulation. The presence of an inflectional point leads to the outer layer rolling up into vortices that interacts with the inner region resulting in a double array of counter rotating vortices before breakdown into turbulence. Past studies have focused on forced wall jet which results in shorter transition region and prominent vortical structures. In the present work, natural transition will be discussed by analysing the coherent structures and scaled frequency spectra. Clear hairpin like structures leaning downstream in the inner region(as in a boundary layer) and leaning upstream in the outerstream (as in a jet) are evident.

Pressure and magnetic field effects on the valence transition of EuRh2Si2

NASA Astrophysics Data System (ADS)

Mitsuda, Akihiro; Kishaba, Eigo; Fujimoto, Takumi; Oyama, Kohei; Wada, Hirofumi; Mizumaki, Masaichiro; Kawamura, Naomi; Ishimatsu, Naoki

2018-05-01

We have measured the X-ray absorption spectra (XAS), electrical resistivity and magnetic susceptibility of EuRh2Si2, which undergoes a valence transition under high pressures. A sharp decrease in the Eu valence determined from the XAS was observed at around 70 K in the temperature dependence at P = 1.2-1.9 GPa. In the temperature dependence of electrical resistivity and magnetic susceptibility, we observed jumps associated with the temperature-induced valence transition under high pressures. The magnetoresistance detected a field-induced valence transition. The results are discussed from the thermodynamic point of view.

Correspondence between solar fine-scale structures in the corona, transition region, and lower atmosphere from collaborative observations

NASA Technical Reports Server (NTRS)

Moses, J. Daniel; Cook, J. W.; Bartoe, J.-D. F.; Brueckner, G. E.; Dere, K. P.; Webb, D. F.; Davis, John M.; Recely, F.; Martin, S. F.; Zirin, H.

1989-01-01

The Soft X-Ray Imaging Payload and the High Resolution Telescope and Spectrograph (HRTS) instrument were launched from White Sands on 11 December 1987 in coordinated sounding rocket flights to investigate the correspondence of coronal and transition region structures, especially the relationship between X-ray bright points (XBPs) and transition region small spatial scale energetic events. The coaligned data from X-ray images are presented along with maps of sites of transition region energetic events observed in C IV (100,000 K), HRTS 1600 A spectroheliograms of the T sub min region and ground based magnetogram and He I 10830 A images.

Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of YbNi3Ga9

NASA Astrophysics Data System (ADS)

Matsubayashi, K.; Hirayama, T.; Yamashita, T.; Ohara, S.; Kawamura, N.; Mizumaki, M.; Ishimatsu, N.; Watanabe, S.; Kitagawa, K.; Uwatoko, Y.

2015-02-01

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence YbNi3Ga9 under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below Pc˜9 GPa where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

Raman spectra and phase transitions in Rb{sub 2}KInF{sub 6} elpasolite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krylov, A. S.; Krylova, S. N., E-mail: slanky@iph.krasn.ru; Vtyurin, A. N.

2011-01-15

The Raman spectra of Rb{sub 2}KInF{sub 6} elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. Several anomalies of internal modes of InF{sub 6} octahedra and low-frequency lattice vibrations, which are related to the structural changes at the transition points, have been found and quantitatively analyzed. The results of a quantitative analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions.

Feasibility study of transit photon correlation anemometer for Ames Research Center unitary wind tunnel plan

NASA Technical Reports Server (NTRS)

Mayo, W. T., Jr.; Smart, A. E.

1979-01-01

A laser transit anemometer measured a two-dimensional vector velocity, using the transit time of scattering particles between two focused and parallel laser beams. The objectives were: (1) the determination of the concentration levels and light scattering efficiencies of naturally occurring, submicron particles in the NASA/Ames unitary wind tunnel and (2) the evaluation based on these measured data of a laser transit anemometer with digital correlation processing for nonintrusive velocity measurement in this facility. The evaluation criteria were the speeds at which point velocity measurements could be realized with this technique (as determined from computer simulations) for given accuracy requirements.

Holographic research on phase transitions for a five dimensional AdS black hole with conformally coupled scalar hair

NASA Astrophysics Data System (ADS)

Li, Hui-Ling; Yang, Shu-Zheng; Zu, Xiao-Tao

2017-01-01

In the framework of holography, we survey the phase structure for a higher dimensional hairy black hole including the effects of the scalar field hair. It is worth emphasizing that, not only black hole entropy, but also entanglement entropy and two point correlation function exhibit the Van der Waals-like phase transition in a fixed scalar charge ensemble. Furthermore, by making use of numerical computation, we show that the Maxwell's equal area law is valid for the first order phase transition. In addition, we also discuss how the hair parameter affects the black hole's phase transition.

Revivals of electron currents and topological-band insulator transitions in 2D gapped Dirac materials

NASA Astrophysics Data System (ADS)

Romera, E.; Bolívar, J. C.; Roldán, J. B.; de los Santos, F.

2016-07-01

We have studied the time evolution of electron wave packets in silicene under perpendicular magnetic and electric fields to characterize topological-band insulator transitions. We have found that at the charge neutrality points, the periodicities exhibited by the wave packet dynamics (classical and revival times) reach maximum values, and that the electron currents reflect the transition from a topological insulator to a band insulator. This provides a signature of topological phase transition in silicene that can be extended to other 2D Dirac materials isostructural to graphene and with a buckled structure and a significant spin-orbit coupling.

Elastic Constants of Ni-Mn-Ga Magnetic Shape Memory Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stipcich, M.; Manosa, L.; Planes, A.

2004-01-01

We have measured the adiabatic second order elastic constants of two Ni-Mn-Ga magnetic shape memory crystals with different martensitic transition temperatures, using ultrasonic methods. The temperature dependence of the elastic constants has been followed across the ferromagnetic transition and down to the martensitic transition temperature. Within experimental errors no noticeable change in any of the elastic constants has been observed at the Curie point. The temperature dependence of the shear elastic constant C' has been found to be very different for the two alloys. Such a different behavior is in agreement with recent theoretical predictions for systems undergoing multi-stage structuralmore » transitions.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

DOE PAGES

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean -Christophe; ...

2017-11-15

In this paper, connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered CH 3NH 3more » + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R- and M-point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean -Christophe

In this paper, connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered CH 3NH 3more » + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R- and M-point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

NASA Astrophysics Data System (ADS)

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean-Christophe; Even, Jacky; Mohite, Aditya D.; Sfeir, Matthew Y.

2017-11-01

Connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered C H3N H3 + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R - and M -point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.

Liquid-gas phase transitions and C K symmetry in quantum field theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishimura, Hiromichi; Ogilvie, Michael C.; Pangeni, Kamal

A general field-theoretic framework for the treatment of liquid-gas phase transitions is developed. Starting from a fundamental four-dimensional field theory at nonzero temperature and density, an effective three-dimensional field theory is derived. The effective field theory has a sign problem at finite density. Although finite density explicitly breaks charge conjugation C , there remains a symmetry under C K , where K is complex conjugation. Here, we consider four models: relativistic fermions, nonrelativistic fermions, static fermions and classical particles. The interactions are via an attractive potential due to scalar field exchange and a repulsive potential due to massive vector exchange.more » The field-theoretic representation of the partition function is closely related to the equivalence of the sine-Gordon field theory with a classical gas. The thermodynamic behavior is extracted from C K -symmetric complex saddle points of the effective field theory at tree level. In the cases of nonrelativistic fermions and classical particles, we find complex saddle point solutions but no first-order transitions, and neither model has a ground state at tree level. The relativistic and static fermions show a liquid-gas transition at tree level in the effective field theory. The liquid-gas transition, when it occurs, manifests as a first-order line at low temperature and high density, terminated by a critical end point. The mass matrix controlling the behavior of correlation functions is obtained from fluctuations around the saddle points. Due to the C K symmetry of the models, the eigenvalues of the mass matrix are not always real but can be complex. This then leads to the existence of disorder lines, which mark the boundaries where the eigenvalues go from purely real to complex. The regions where the mass matrix eigenvalues are complex are associated with the critical line. In the case of static fermions, a powerful duality between particles and holes allows for the analytic determination of both the critical line and the disorder lines. Depending on the values of the parameters, either zero, one, or two disorder lines are found. Our numerical results for relativistic fermions give a very similar picture.« less

Liquid-gas phase transitions and C K symmetry in quantum field theories

DOE PAGES

Nishimura, Hiromichi; Ogilvie, Michael C.; Pangeni, Kamal

2017-04-04

A general field-theoretic framework for the treatment of liquid-gas phase transitions is developed. Starting from a fundamental four-dimensional field theory at nonzero temperature and density, an effective three-dimensional field theory is derived. The effective field theory has a sign problem at finite density. Although finite density explicitly breaks charge conjugation C , there remains a symmetry under C K , where K is complex conjugation. Here, we consider four models: relativistic fermions, nonrelativistic fermions, static fermions and classical particles. The interactions are via an attractive potential due to scalar field exchange and a repulsive potential due to massive vector exchange.more » The field-theoretic representation of the partition function is closely related to the equivalence of the sine-Gordon field theory with a classical gas. The thermodynamic behavior is extracted from C K -symmetric complex saddle points of the effective field theory at tree level. In the cases of nonrelativistic fermions and classical particles, we find complex saddle point solutions but no first-order transitions, and neither model has a ground state at tree level. The relativistic and static fermions show a liquid-gas transition at tree level in the effective field theory. The liquid-gas transition, when it occurs, manifests as a first-order line at low temperature and high density, terminated by a critical end point. The mass matrix controlling the behavior of correlation functions is obtained from fluctuations around the saddle points. Due to the C K symmetry of the models, the eigenvalues of the mass matrix are not always real but can be complex. This then leads to the existence of disorder lines, which mark the boundaries where the eigenvalues go from purely real to complex. The regions where the mass matrix eigenvalues are complex are associated with the critical line. In the case of static fermions, a powerful duality between particles and holes allows for the analytic determination of both the critical line and the disorder lines. Depending on the values of the parameters, either zero, one, or two disorder lines are found. Our numerical results for relativistic fermions give a very similar picture.« less

Four-body trajectory optimization

NASA Technical Reports Server (NTRS)

Pu, C. L.; Edelbaum, T. N.

1974-01-01

A comprehensive optimization program has been developed for computing fuel-optimal trajectories between the earth and a point in the sun-earth-moon system. It presents methods for generating fuel optimal two-impulse trajectories which may originate at the earth or a point in space and fuel optimal three-impulse trajectories between two points in space. The extrapolation of the state vector and the computation of the state transition matrix are accomplished by the Stumpff-Weiss method. The cost and constraint gradients are computed analytically in terms of the terminal state and the state transition matrix. The 4-body Lambert problem is solved by using the Newton-Raphson method. An accelerated gradient projection method is used to optimize a 2-impulse trajectory with terminal constraint. The Davidon's Variance Method is used both in the accelerated gradient projection method and the outer loop of a 3-impulse trajectory optimization problem.

Investigation of indirect excitons in bulk 2H-MoS2 using transmission electron energy-loss spectroscopy.

PubMed

Habenicht, Carsten; Schuster, Roman; Knupfer, Martin; Büchner, Bernd

2018-05-23

We have investigated indirect excitons in bulk 2H-MoS 2 using transmission electron energy-loss spectroscopy. The electron energy-loss spectra were measured for various momentum transfer values parallel to the [Formula: see text] and [Formula: see text] directions of the Brillouin zone. The results allowed the identification of the indirect excitons between the valence band K v and conduction band Λ c points, the Γ v and K c points as well as adjacent K v and [Formula: see text] points. The energy-momentum dispersions for the K v -Λ c , Γ v -K c and K v1 -[Formula: see text] excitons along the [Formula: see text] line are presented. The former two transitions exhibit a quadratic dispersion which allowed calculating their effective exciton masses based on the effective mass approximation. The K v1 -[Formula: see text] transition follows a more linear dispersion relationship.

Mixed Spin-1/2 and Spin-5/2 Model by Renormalization Group Theory: Recursion Equations and Thermodynamic Study

NASA Astrophysics Data System (ADS)

Antari, A. El; Zahir, H.; Hasnaoui, A.; Hachem, N.; Alrajhi, A.; Madani, M.; Bouziani, M. El

2018-04-01

Using the renormalization group approximation, specifically the Migdal-Kadanoff technique, we investigate the Blume-Capel model with mixed spins S = 1/2 and S = 5/2 on d-dimensional hypercubic lattice. The flow in the parameter space of the Hamiltonian and the thermodynamic functions are determined. The phase diagram of this model is plotted in the (anisotropy, temperature) plane for both cases d = 2 and d = 3 in which the system exhibits the first and second order phase transitions and critical end-points. The associated fixed points are drawn up in a table, and by linearizing the transformation at the vicinity of these points, we determine the critical exponents for d = 2 and d = 3. We have also presented a variation of the free energy derivative at the vicinity of the first and second order transitions. Finally, this work is completed by a discussion and comparison with other approximation.

Mechanical Metamaterials with Negative Compressibility Transitions

NASA Astrophysics Data System (ADS)

Motter, Adilson

2015-03-01

When tensioned, ordinary materials expand along the direction of the applied force. In this presentation, I will explore network concepts to design metamaterials exhibiting negative compressibility transitions, during which the material undergoes contraction when tensioned (or expansion when pressured). Such transitions, which are forbidden in thermodynamic equilibrium, are possible during the decay of metastable, super-strained states. I will introduce a statistical physics theory for negative compressibility transitions, derive a first-principles model to predict these transitions, and present a validation of the model using molecular dynamics simulations. Aside from its immediate mechanical implications, our theory points to a wealth of analogous inverted responses, such as inverted susceptibility or heat-capacity transitions, allowed when considering realistic scales. This research was done in collaboration with Zachary Nicolaou, and was supported by the National Science Foundation and the Alfred P. Sloan Foundation.

Ashkin-Teller criticality and weak first-order behavior of the phase transition to a fourfold degenerate state in two-dimensional frustrated Ising antiferromagnets

NASA Astrophysics Data System (ADS)

Liu, R. M.; Zhuo, W. Z.; Chen, J.; Qin, M. H.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.

2017-07-01

We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses. Furthermore, a similar behavior of the transition to the fourfold single-stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the fourfold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior.

Hybrid Percolation Transition in Cluster Merging Processes: Continuously Varying Exponents

NASA Astrophysics Data System (ADS)

Cho, Y. S.; Lee, J. S.; Herrmann, H. J.; Kahng, B.

2016-01-01

Consider growing a network, in which every new connection is made between two disconnected nodes. At least one node is chosen randomly from a subset consisting of g fraction of the entire population in the smallest clusters. Here we show that this simple strategy for improving connection exhibits a more unusual phase transition, namely a hybrid percolation transition exhibiting the properties of both first-order and second-order phase transitions. The cluster size distribution of finite clusters at a transition point exhibits power-law behavior with a continuously varying exponent τ in the range 2 <τ (g )≤2.5 . This pattern reveals a necessary condition for a hybrid transition in cluster aggregation processes, which is comparable to the power-law behavior of the avalanche size distribution arising in models with link-deleting processes in interdependent networks.

Studies of a general flat space/boson star transition model in a box through a language similar to holographic superconductors

NASA Astrophysics Data System (ADS)

Peng, Yan

2017-07-01

We study a general flat space/boson star transition model in quasi-local ensemble through approaches familiar from holographic superconductor theories. We manage to find a parameter ψ 2, which is proved to be useful in disclosing properties of phase transitions. In this work, we explore effects of the scalar mass, scalar charge and Stückelberg mechanism on the critical phase transition points and the order of transitions mainly from behaviors of the parameter ψ 2. We mention that properties of transitions in quasi-local gravity are strikingly similar to those in holographic superconductor models. We also obtain an analytical relation ψ 2 ∝ ( μ - μ c )1/2, which also holds for the condensed scalar operator in the holographic insulator/superconductor system in accordance with mean field theories.

Implications of Weak Link Effects on Thermal Characteristics of Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Bailey, Catherine

2011-01-01

Weak link behavior in transition-edge sensor (TES) devices creates the need for a more careful characterization of a device's thermal characteristics through its transition. This is particularly true for small TESs where a small change in the measurement current results in large changes in temperature. A highly current-dependent transition shape makes accurate thermal characterization of the TES parameters through the transition challenging. To accurately interpret measurements, especially complex impedance, it is crucial to know the temperature-dependent thermal conductance, G(T), and heat capacity, C(T), at each point through the transition. We will present data illustrating these effects and discuss how we overcome the challenges that are present in accurately determining G and T from IV curves. We will also show how these weak link effects vary with TES size.

Competition of density waves and quantum multicritical behavior in Dirac materials from functional renormalization

NASA Astrophysics Data System (ADS)

Classen, Laura; Herbut, Igor F.; Janssen, Lukas; Scherer, Michael M.

2016-03-01

We study the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dimensional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics near the multicritical point at which the semimetallic and the spin- and charge-density-wave phases meet. With the help of a functional renormalization group approach, we are able to reveal a complex structure of fixed points, the stability properties of which decisively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compared to the previous first-order ɛ expansion. For small Nf, the universal behavior near the multicritical point is determined by the chiral Heisenberg universality class supplemented by a decoupled, purely bosonic, Ising sector. At large Nf, a novel fixed point with nontrivial couplings between all sectors becomes stable. At intermediate Nf, including the graphene case (Nf=2 ), no stable and physically admissible fixed point exists. Graphene's phase diagram in the vicinity of the intersection between the semimetal, antiferromagnetic, and staggered density phases should consequently be governed by a triple point exhibiting first-order transitions.

Towards a critical transition theory under different temporal scales and noise strengths

NASA Astrophysics Data System (ADS)

Shi, Jifan; Li, Tiejun; Chen, Luonan

2016-03-01

The mechanism of critical phenomena or critical transitions has been recently studied from various aspects, in particular considering slow parameter change and small noise. In this article, we systematically classify critical transitions into three types based on temporal scales and noise strengths of dynamical systems. Specifically, the classification is made by comparing three important time scales τλ, τtran, and τergo, where τλ is the time scale of parameter change (e.g., the change of environment), τtran is the time scale when a particle or state transits from a metastable state into another, and τergo is the time scale when the system becomes ergodic. According to the time scales, we classify the critical transition behaviors as three types, i.e., state transition, basin transition, and distribution transition. Moreover, for each type of transition, there are two cases, i.e., single-trajectory transition and multitrajectory ensemble transition, which correspond to the transition of individual behavior and population behavior, respectively. We also define the critical point for each type of critical transition, derive several properties, and further propose the indicators for predicting critical transitions with numerical simulations. In addition, we show that the noise-to-signal ratio is effective to make the classification of critical transitions for real systems.

Critical points of metal vapors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khomkin, A. L., E-mail: alhomkin@mail.ru; Shumikhin, A. S.

2015-09-15

A new method is proposed for calculating the parameters of critical points and binodals for the vapor–liquid (insulator–metal) phase transition in vapors of metals with multielectron valence shells. The method is based on a model developed earlier for the vapors of alkali metals, atomic hydrogen, and exciton gas, proceeding from the assumption that the cohesion determining the basic characteristics of metals under normal conditions is also responsible for their properties in the vicinity of the critical point. It is proposed to calculate the cohesion of multielectron atoms using well-known scaling relations for the binding energy, which are constructed for mostmore » metals in the periodic table by processing the results of many numerical calculations. The adopted model allows the parameters of critical points and binodals for the vapor–liquid phase transition in metal vapors to be calculated using published data on the properties of metals under normal conditions. The parameters of critical points have been calculated for a large number of metals and show satisfactory agreement with experimental data for alkali metals and with available estimates for all other metals. Binodals of metals have been calculated for the first time.« less

Inversion symmetry breaking induced triply degenerate points in orderly arranged PtSeTe family materials

NASA Astrophysics Data System (ADS)

Xiao, R. C.; Cheung, C. H.; Gong, P. L.; Lu, W. J.; Si, J. G.; Sun, Y. P.

2018-06-01

k paths exactly with symmetry allow to find triply degenerate points (TDPs) in band structures. The paths that host the type-II Dirac points in PtSe2 family materials also have the spatial symmetry. However, due to Kramers degeneracy (the systems have both inversion symmetry and time reversal symmetry), the crossing points in them are Dirac ones. In this work, based on symmetry analysis, first-principles calculations, and method, we predict that PtSe2 family materials should undergo topological transitions if the inversion symmetry is broken, i.e. the Dirac fermions in PtSe2 family materials split into TDPs in PtSeTe family materials (PtSSe, PtSeTe, and PdSeTe) with orderly arranged S/Se (Se/Te). It is different from the case in high-energy physics that breaking inversion symmetry I leads to the splitting of Dirac fermion into Weyl fermions. We also address a possible method to achieve the orderly arranged in PtSeTe family materials in experiments. Our study provides a real example that Dirac points transform into TDPs, and is helpful to investigate the topological transition between Dirac fermions and TDP fermions.

Effective scheme to determine accurate defect formation energies and charge transition levels of point defects in semiconductors

NASA Astrophysics Data System (ADS)

Yao, Cang Lang; Li, Jian Chen; Gao, Wang; Tkatchenko, Alexandre; Jiang, Qing

2017-12-01

We propose an effective method to accurately determine the defect formation energy Ef and charge transition level ɛ of the point defects using exclusively cohesive energy Ecoh and the fundamental band gap Eg of pristine host materials. We find that Ef of the point defects can be effectively separated into geometric and electronic contributions with a functional form: Ef=χ Ecoh+λ Eg , where χ and λ are dictated by the geometric and electronic factors of the point defects (χ and λ are defect dependent). Such a linear combination of Ecoh and Eg reproduces Ef with an accuracy better than 5% for electronic structure methods ranging from hybrid density-functional theory (DFT) to many-body random-phase approximation (RPA) and experiments. Accordingly, ɛ is also determined by Ecoh/Eg and the defect geometric/electronic factors. The identified correlation is rather general for monovacancies and interstitials, which holds in a wide variety of semiconductors covering Si, Ge, phosphorenes, ZnO, GaAs, and InP, and enables one to obtain reliable values of Ef and ɛ of the point defects for RPA and experiments based on semilocal DFT calculations.

Rate of recovery from perturbations as a means to forecast future stability of living systems.

PubMed

Ghadami, Amin; Gourgou, Eleni; Epureanu, Bogdan I

2018-06-18

Anticipating critical transitions in complex ecological and living systems is an important need because it is often difficult to restore a system to its pre-transition state once the transition occurs. Recent studies demonstrate that several indicators based on changes in ecological time series can indicate that the system is approaching an impending transition. An exciting question is, however, whether we can predict more characteristics of the future system stability using measurements taken away from the transition. We address this question by introducing a model-less forecasting method to forecast catastrophic transition of an experimental ecological system. The experiment is based on the dynamics of a yeast population, which is known to exhibit a catastrophic transition as the environment deteriorates. By measuring the system's response to perturbations prior to transition, we forecast the distance to the upcoming transition, the type of the transition (i.e., catastrophic/non-catastrophic) and the future equilibrium points within a range near the transition. Experimental results suggest a strong potential for practical applicability of this approach for ecological systems which are at risk of catastrophic transitions, where there is a pressing need for information about upcoming thresholds.

Evidence for a universal localization transition underlying the glass transition

NASA Astrophysics Data System (ADS)

Simmons, David; Hung, Jui-Hsiang; Patra, Tarak; Meenakshisundaram, Venkatesh; Mangalara, Jayachandra Hari

The glass transition is a ubiquitous pathway to the development of solid-like character, occurring in materials ranging from polymers to metals. Despite its technological and fundamental importance across diverse materials, the underlying nature of the glass transition remains a durable open question. Here we describe results from high-throughput simulations of the glass transition in metals, polymers, small organic molecules, and organics, indicating that a universal particle localization transition underlies the dynamic glass transition. We find that a single adjustable parameter is sufficient to describe the nonuniversal growth in relaxation time resulting from this localization event. These results point to an opportunity to advance the modern understanding of the glass transition by refocusing attention on the onset of localization rather than the growth in relaxation time as the key experimental observable. This work was made possible by generous support from the W. M. Keck Foundation. This material is based in part on work sup-ported by the National Science Foundation NSF Career Award Grant Number DMR1554920.

Epidemic models for phase transitions: application to a physical gel

NASA Astrophysics Data System (ADS)

Bilge, A. H.; Pekcan, O.; Kara, S.; Ogrenci, A. S.

2017-09-01

Carrageenan gels are characterized by reversible sol-gel and gel-sol transitions under cooling and heating processes and these transitions are approximated by generalized logistic growth curves. We express the transitions of carrageenan-water system, as a representative of reversible physical gels, in terms of a modified Susceptible-Infected-Susceptible epidemic model, as opposed to the Susceptible-Infected-Removed model used to represent the (irreversible) chemical gel formation in the previous work. We locate the gel point Tc of sol-gel and gel-sol transitions and we find that, for the sol-gel transition (cooling), Tc > Tsg (transition temperature), i.e. Tc is earlier in time for all carrageenan contents and moves forward in time and gets closer to Tsg as the carrageenan content increases. For the gel-sol transition (heating), Tc is relatively closer to Tgs; it is greater than Tgs, i.e. later in time for low carrageenan contents and moves backward as carrageenan content increases.

Pressure induced structural phase transition in IB transition metal nitrides compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soni, Shubhangi; Kaurav, Netram, E-mail: netramkaurav@yahoo.co.uk; Jain, A.

2015-06-24

Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbormore » ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.« less

The role and significance of nurses in managing transitions to palliative care: a qualitative study

PubMed Central

Kirby, Emma; Broom, Alex; Good, Phillip

2014-01-01

Objectives Nurses are generally present, and often influential, in supporting patient and family acceptance of medical futility and in assisting doctors in negotiating referral to palliative care. Yet the specificities of the nursing role and how nurses may contribute to timely and effective referrals is not well understood. This study aimed to systematically explore hospital-based nurses’ accounts of the transition to palliative care, and the potential role of nurses in facilitating more effective palliative care transitions. Design Qualitative study using semistructured interviews. Setting Two health services with public as well as private clinical environments in a major metropolitan area of Australia. Participants Hospital-based nurses (n=20) who regularly work with patients at the point of referral and in managing transitions to palliative care. Results Four significant themes emerged from thematic analysis. These include: (1) professional dynamics and the roles played by nurses in initiating the transition to palliative care; (2) the value of nurses’ informal interactions in timely and effective transitions; (3) the emerging challenge of managing task-oriented nursing versus intense emotional nursing work at the point of medical futility and (4) the emotional burden experienced by nurses within this clinical context. Nurses self-reported occupying critical albeit complex roles in the management of medical futility and the transition to palliative care. They reported experiencing significant emotional burden in balancing interpersonal and interprofessional relationships during this time. Conclusions The results suggest that nurses may be utilised in a more formalised and systematic fashion in the context of managing medical futility and the need to topicalise the transition, with the focus shifted away from medical referrals towards more team-based and patient-centred timely transitions. Further research focused on the experiences of doctors, allied health professionals, patients and families is required to provide a broader interdisciplinary understanding of futility and contributions to the negotiation of palliative care. PMID:25270859

Non-linear education gradient across the nutrition transition: mothers' overweight and the population education transition.

PubMed

Jeon, Haram; Salinas, Daniel; Baker, David P

2015-12-01

Previous studies found that developed and developing countries present opposite education-overweight gradients but have not considered the dynamics at different levels of national development. An inverted U-shaped curve is hypothesized to best describe the education-overweight association. It is also hypothesized that as the nutrition transition unfolds within nations the shape of education-overweight curve changes. Multilevel logistic regression was used to estimate the moderating effect of the nutrition transition at the population level on the education-overweight gradient. At the individual level, a non-linear estimate of the education association was used to assess the optimal functional form of the association across the nutrition transition. Twenty-two administrations of the Demographic and Health Survey, collected at different time points across the nutrition transition in nine Latin American/Caribbean countries. Mothers of reproductive age (15-49 years) in each administration (n 143 258). In the pooled sample, a non-linear education gradient on mothers' overweight was found; each additional year of schooling increases the probability of being overweight up to the end of primary schooling, after which each additional year of schooling decreases the probability of overweight. Also, as access to diets high in animal fats and sweeteners increases over time, the curve's critical point moves to lower education levels, the detrimental positive effect of education diminishes, and both occur as the overall risk of overweight increases with greater access to harmful diets. Both hypotheses were supported. As the nutrition transition progresses, the education-overweight curve shifts steadily to a negative linear association with a higher average risk of overweight; and education, at increasingly lower levels, acts as a 'social vaccine' against increasing risk of overweight. These empirical patterns fit the general 'population education transition' curve hypothesis about how education's influences on health risks are contextualized across population transitions.

Active Oxidation of SiC

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Myers,Dwight L.; Harder, Bryan J.

2011-01-01

The high temperature oxidation of silicon carbide occurs in either a passive or active mode, depending on temperature and oxygen potential. Passive oxidation forms a protective oxide film which limits attack of the SiC:SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g.) Active oxidation forms a volatile oxide and leads to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g). The transition points and rates of active oxidation are a major issue. Previous studies are reviewed and the leading theories of passive/active transitions summarized. Comparisons are made to the active/passive transitions in pure Si, which are relatively well-understood. Critical questions remain about the difference between the active-to-passive transition and passive-to-active transition. For Si, Wagner [2] points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. This suggests a significant oxygen potential difference between these two transitions and our experiments confirm this. For Si, the initial stages of active oxidation are characterized by the formation of SiO(g) and further oxidation to SiO2(s) as micron-sized rods, with a distinctive morphology. SiC shows significant differences. The active-to-passive and the passive-to-active transitions are close. The SiO2 rods only appear as the passive film breaks down. These differences are explained in terms of the reactions at the SiC/SiO2 interface. In order to understand the breakdown of the passive film, pre-oxidation experiments are conducted. These involve forming dense protective scales of 0.5, 1, and 2 microns and then subjecting the samples with these scales to a known active oxidation environment. Microstructural studies show that SiC/SiO2 interfacial reactions lead to a breakdown of the scale with a distinct morphology.

A new interpretation of the Besnus transition in monoclinic pyrrhotite

NASA Astrophysics Data System (ADS)

Gehring, Andreas

2016-04-01

Non-stoichiometric monoclinic 4C pyrrhotite (ideal formula: Fe7S8) is a major magnetic remanence carrier in the Earth's crust and in extraterrestrial materials. Because of its low-temperature magnetic transition around 30 K also known as Besnus transition, this mineral phase is easily detectable in natural samples. Considering the rock magnetic literature, an intrinsic origin of the Besnus transition similar to that of the Verwey transition has generally been assumed. Although the physical properties of pyrrhotite have intensively been studied, the mechanism behind the pronounced change in magnetization at the low-temperature transition is still debated. To address this question we performed magnetization experiments on a natural pyrrhotite crystal (Fe6.6S8) that consists of an epitaxial intergrowth of a commensurate 4C and an incommensurate 5C* superstructure that are different in their defect structure (1,2). The occurrence of two monoclinic superstructures detected by X-ray diffractometry is magnetically confirmed by symmetric inflection points in hysteresis measurements above the transition at about 30 K. The disappearance of the inflection points and the associated change of the hysteresis parameters indicate that the two superstructures become strongly coupled to form a unitary magnetic anisotropy system at the transition. From this it follows that the Besnus transition in monoclinic pyrrhotite is an extrinsic magnetic phenomenon with respect to the 4C superstructure and therefore the physics behind it is in fact different from that of the well-known Verwey transition. Finally, this novel interpretation explains the rock magnetic data for the low-temperature transition that has been reported for monoclinic pyrrhotite. It will also provide deeper understanding of magnetism in monoclinic pyrrhotite, which in turn will enable a more profound insight to the magnetization properties of the Earth's crust. 1.) Charilaou, M., Kind, J., Koulialias, D., Weidler, P.G., Mensing, C., Löffler, J.F. & Gehring, A.U., 2015. J. Appl. Phys., 118, 083903. 2.) Koulialias, D., Kind, J., Charilaou, M., Weidler, P.G., Löffler, J.F. & Gehring, A.U. 2016. Geophys. J. Int., 204, 961-967.

Spacelab experiment definition study on phase transition and critical phenomena in fluids: Interim report on experimental justification

NASA Technical Reports Server (NTRS)

Moldover, M. R.; Hocken, M. R.; Gammon, R. W.; Sengers, J. V.

1976-01-01

Pure fluids and fluid mixtures near critical points are identified and are related to the progress of several disciplines. Consideration is given to thermodynamic properties, transport properties, and the complex nonlinear phenomena which occur when fluids undergo phase transitions in the critical region. The distinction is made between practical limits which may be extended by advances in technology and intrinsic ones which arise from the modification of fluid properties by the earth's gravitational field. The kinds of experiments near critical points which could best exploit the low gravity environment of an orbiting laboratory are identified. These include studies of the index of refraction, constant volume specific heat, and phase separation.

Nanoscale interfacial defect shedding in a growing nematic droplet.

PubMed

Gurevich, Sebastian; Provatas, Nikolas; Rey, Alejandro

2017-08-01

Interfacial defect shedding is the most recent known mechanism for defect formation in a thermally driven isotropic-to-nematic phase transition. It manifests in nematic-isotropic interfaces going through an anchoring switch. Numerical computations in planar geometry established that a growing nematic droplet can undergo interfacial defect shedding, nucleating interfacial defect structures that shed into the bulk as +1/2 point defects. By extending the study of interfacial defect shedding in a growing nematic droplet to larger length and time scales, and to three dimensions, we unveil an oscillatory growth mode involving shape and anchoring transitions that results in a controllable regular distributions of point defects in planar geometry, and complex structures of disclination lines in three dimensions.

Maxwell’s equal area law for Lovelock thermodynamics

NASA Astrophysics Data System (ADS)

Xu, Hao; Xu, Zhen-Ming

We present the construction of Maxwell’s equal area law for the Guass-Bonnet AdS black holes in d = 5, 6 and third-order Lovelock AdS black holes in d = 7, 8. The equal area law can be used to find the number and location of the points of intersection in the plots of Gibbs free energy, so that we can get the thermodynamically preferred solution which corresponds to the first-order phase transition. We obtain the radius of the small and large black holes in the phase transition which share the same Gibbs free energy. The case with two critical points is explored in much more details. The latent heat is also studied.

Influence of crystal fields on the quasimetallic reflection spectra of crystals: Optical spectra of polymorphs of a squarylium dye

NASA Astrophysics Data System (ADS)

Tristani-Kendra, M.; Eckhardt, C. J.

1984-08-01

The reflection and Kramers-Kronig absorption spectra have been obtained from the monoclinic and triclinic polymorphs of a squarylium dye, 2,4-bis(4-diethylamino-2-hydroxy phenyl) cyclobutadienediylium-1,3-diolate. The extremely different optical responses were found to arise from two molecular singlet transitions of essentially long axis polarization. Successful application of a four oscillator molecular exciton-polariton theory required the use of point charge densities rather than point dipoles in an extension of the theory which employed both interactions between the two singlets as well as a frequency dependent lattice damping. An intermolecular charge transfer transition is also assigned.

Curriculum on the European Policy Agenda: Global Transitions and Learning Outcomes from Transnational and National Points of View

ERIC Educational Resources Information Center

Sivesind, Kirsten; Wahlström, Ninni

2016-01-01

This special issue examines curricula and their histories as they have evolved throughout the 21st century as part of transnational and national education policies. With a specific focus on the policy transitions that are taking place in Europe, the articles demonstrate how curriculum making processes move in different directions, following their…

Tool Use and the Development of the Function Concept: From Repeated Calculations to Functional Thinking

ERIC Educational Resources Information Center

Doorman, Michiel; Drijvers, Paul; Gravemeijer, Koeno; Boon, Peter; Reed, Helen

2012-01-01

The concept of function is a central but difficult topic in secondary school mathematics curricula, which encompasses a transition from an operational to a structural view. The question in this paper is how the use of computer tools may foster this transition. With domain-specific pedagogical knowledge on the learning of function as a point of…

Signs and Transitions: Do They Differ Phonetically and Does It Matter?

ERIC Educational Resources Information Center

Jantunen, Tommi

2013-01-01

The point of departure of this article is the cluster of three pre-theoretical presuppositions (P) governing modern research on sign languages: (1) that a stream of signing consists of signs (S) and transitions (T), (2) that only Ss are linguistically relevant units, and (3) that there is a qualitative (e.g., phonetic) difference between Ss and…