Triangular Cycles Research Articles

Decomposing planar graphs without triangular short cycles into a matching and a 3-colorable graph

Decomposing planar graphs without triangular short cycles into a matching and a 3-colorable graph

Learning a Metric for Multimodal Medical Image Registration without Supervision Based on Cycle Constraints.

Deep learning based medical image registration remains very difficult and often fails to improve over its classical counterparts where comprehensive supervision is not available, in particular for large transformations—including rigid alignment. The use of unsupervised, metric-based registration networks has become popular, but so far no universally applicable similarity metric is available for multimodal medical registration, requiring a trade-off between local contrast-invariant edge features or more global statistical metrics. In this work, we aim to improve over the use of handcrafted metric-based losses. We propose to use synthetic three-way (triangular) cycles that for each pair of images comprise two multimodal transformations to be estimated and one known synthetic monomodal transform. Additionally, we present a robust method for estimating large rigid transformations that is differentiable in end-to-end learning. By minimising the cycle discrepancy and adapting the synthetic transformation to be close to the real geometric difference of the image pairs during training, we successfully tackle intra-patient abdominal CT-MRI registration and reach performance on par with state-of-the-art metric-supervision and classic methods. Cyclic constraints enable the learning of cross-modality features that excel at accurate anatomical alignment of abdominal CT and MRI scans.

Electronic Structure and Magnetic Properties of Mixed-Ligand Cobalt Complexes Containing Organogermanium Triangulenes

Computational modeling of cobalt(II) diketonate adducts with o-benzoquinones modified with organogermanium triangular cycles of different size has been performed using the density functional theory method. Energy characteristics of the isomers of the investigated compounds have been found to be determined by the substituents in terminal diketone ligands. Paramagnetism of all the states of the studied molecules has been predicted. The systems, magnetic properties of which can be switched as a result of intramolecular electron transfer between the cobalt ion and the ligand, have been revealed.

Out-of-Phase TMF lifetime calculation of EN-GJS-600 (ASTM 80-55-06) ductile cast iron based on strain increase tests and evaluation of cyclic deformation behavior in isothermal measuring intervals

Components of internal combustion engines not only undergo mechanical high and low-cycle fatigue but also thermally induced loadings during start-stop and load changes. Accordingly, an efficient lifetime calculation method of the ductile cast iron EN-GJS-600 for Out-of-Phase thermomechanical fatigue (OP TMF) loading was developed based on Morrow’s relation between cyclic deformation and fatigue lifetime behavior. As an alternative to established fracture mechanics based approaches, the slope of the Wöhler curve is calculated from data determined in at least one each of a TMF strain increase and TMF constant amplitude test. Based on the Physically Based Lifetime calculation (PhyBaL) method previously published for isothermal low cycle fatigue (LCF) and high cycle fatigue (HCF) loadings, and data taken from only one strain increase and at least one constant amplitude OP TMF test, the Wöhler curve can be described as according well with constant amplitude OP TMF tests performed for validation. In the present work, triangular TMF cycles were applied at 5 mHz (0.005 Hz) with a temperature range from 50 to 350 °C. Cyclic deformation behavior as input data for calculation of the slope of the Wöhler curve was determined by stepwise increases of mechanical strain amplitude in OP TMF tests. By constant amplitude tests at different mechanical strain amplitudes, the lifetime and cyclic deformation behavior at OP TMF loading were determined for validation. Moreover, applicability of measurement cycles at constant temperature and low stress amplitude applied in defined intervals of regular OP TMF cycles proved to match the OP TMF cyclic deformation behavior well. This opens up the prospect of characterizing cyclic deformation behavior in more complex, near service TMF cycles as a baseline for lifetime assessment using the PhyBaL approach outlined above.

Modeling discharge coefficient of normal and inverted orientation labyrinth weirs using machine learning techniques

A labyrinth weir is a polygonal overflow weir that is characterized by its hydraulic performance and distinct geometric shape (triangular, trapezoidal or rectangular cycles). The present study provides new knowledge and design information on the performance and operation of adaptive neuro-fuzzy inference system (ANFIS) and gene expression programming (GEP) techniques for predicting discharge coefficient of labyrinth weirs in a flume. Discharge coefficient, Cd, was considered as a function of headwater ratio, upstream Froude number, magnification ratio, sidewall angle, apex ratio, and cycle width ratio (dimensionless parameters). The records obtained through 300 laboratory data sets were used to determine the Cd of labyrinth weirs. The results showed that the best GEP model determined the Cd values of the normal and inverted orientation labyrinth weir with a RMSE of 0.0139, 0.590, DC of 0.977, 0.852 and R of 0.996, 0.923, respectively by using the four dimensionless parameters of Fr, HT/P, Lc/W and A/w as input variables. The best ANFIS model determined the Cd value of the normal orientation labyrinth weir by using all six dimensionless parameters (RMSE = 0.0110, DC = 0.964, R = 0.987) and inverted orientation labyrinth weir by using three dimensionless parameters of HT/P, α, and w/p as input variables (RMSE = 0.0290, DC = 0.952, R = 0.987). The results of sensitivity analysis showed that Fr in the GEP model and Fr and HT/P in the ANFIS model are the most effective variables for determining Cd for normal and inverted orientation labyrinth weirs, respectively. It was found that when low headwater ratios were eliminated from analysis, performance accuracy of the models was improved.

Effect of accelerated ageing tests on PBI HTPEM fuel cells performance degradation

The study presented in this paper aims to evaluate the performance degradation of Polybenzimidazole (PBI) based High Temperature PEM (HTPEM) fuel cells subjected to different ageing tests, according to a methodology already used by the authors. Three HTPEM Membrane Electrode Assemblies (MEAs) were characterized before and after different aging tests and performance compared. The three MEAs have been named MEA C, MEA D and MEA E. MEA C was subjected to 100,000 triangular sweep cycles between Open Circuit Voltage (OCV) and 0.5 A/cm2 with 2 s of permanence at OCV at each cycle. MEA D and MEA E were subjected to 440 h of operation at constant load of 0.22 A/cm2. In order to assess the cell performance, polarization curves, Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were recorded during the ageing tests. Degradation rates have been obtained for MEA C (44 μV/h), for MEA D (30 μV/h) and for MEA E (29 μV/h). ECSA (Electrochemical Surface Area) has been calculated for the three MEAs showing a reduction of approximately 50% for MEA C and of approximately 30% for MEA D and MEA E. Polarization curves during aging tests confirm that load cycling is more detrimental. A comparison with data obtained by the authors in a previous research seems to confirm the repeatability of the test protocol used.

(Invited) The Influence of the Carbon Support and Platinum Particles Size on Degradation of Cathode for Low Platinum-Loading Catalyst Layer

We demonstrated the ability to control the platinum particle size in the synthesis of carbon supported Pt (Pt/C) electrocatalyst with reactive spray deposition technology (RSDT). The degradation of Pt cathode with loading of 0.1 mg/cm2 in membrane electrode assembly (MEA) under simulated drive cycles (30000 triangular wave cycles between 0.6 and 1.0 VRHE) showed similar electrochemical surface area (ECSA) at the end of life (EOL), regardless of the initial Pt particle size or carbon support type. However, it is possible to reduce the loss of ECSA using a gradient catalyst layer consisting of a 6 mm layer with Pt particles of 5 nm toward the membrane and another 6 mm layer with Pt particles of 2 nm toward the GDL. Microscopy studies suggested that the gradient catalyst layer have less Pt loss% into the electrolyte, thereby maintained higher ECSA at EOL.

Numerical study of liquid phase diffusion growth of SiGe subjected to accelerated crucible rotation

The effect of accelerated crucible rotation technique (ACRT) on liquid phase diffusion (LPD) growth of SixGe1−x crystal has been investigated numerically. Transient, axisymmetric simulations have been carried out for triangular and trapezoidal ACRT cycles. Natural convection driven flow in the early growth hours is found to be modified by the ACRT induced Ekman flow. Results also reveal that a substantial mixing in the solution can be induced by the application of ACRT in the later hours of growth which is otherwise a diffusion dominated growth period for LPD growth technique. A comparison is drawn to the cases of stationary crucible and crucible rotating at a constant speed examined previously for this growth system by Sekhon and Dost (J. Cryst. Growth 430 (2015) 63). It is found that a superior interface flattening effect and radial compositional uniformity along the growth interface can be accomplished by employing ACRT at 12rpm than that which could be achieved by using steady crucible rotation at 25rpm, owing to the higher time averaged growth velocity achieved in the former case. Furthermore, minor differences are also predicted in the results obtained for trapezoidal and triangular ACRT cycles.

Chow groups of tensor triangulated categories

We recall P. Balmer's definition of tensor triangular Chow group for a tensor triangulated category K and explore some of its properties. We give a proof that for a suitably nice scheme X it recovers the usual notion of Chow group from algebraic geometry when we put K=Dperf(X). Furthermore, we identify a class of functors for which tensor triangular Chow groups behave functorially and show that (for suitably nice schemes) proper push-forward and flat pull-back of algebraic cycles can be interpreted as being induced by the derived inverse and direct image functors between the bounded derived categories of the involved schemes. We also compute some examples for derived and stable categories from modular representation theory, where we obtain tensor triangular cycle groups with torsion coefficients. This illustrates our point of view that tensor triangular cycles are elements of a certain Grothendieck group, rather than Z-linear combinations of closed subspaces of some topological space.

14 kA HTS Current Leads with one 4.8 K Helium Stream for the Prototype Test Facility at GSI

The key part of the international FAIR project in Darmstadt, Germany, is the synchrotron SIS100, for which superconducting mag- nets are employed. For the First of Series Dipole a pair of HTS current leads with a nominal current of 14 kA DC were specified, manufactured and successfully tested. The motivation for these current leads was a high operation current and the liquefaction limit of 1g/s of the cooling plant. In the design it has to be taken into account that per lead only one helium stream is available for the entirely inner cooling. For I=0 (8 kA DC) only 0.25g/s/lead (0.38) were necessary to be compared to 0.365 (0.51) specified. Slow ramping with 50 A/s up to 17 kA was accomplished. Triangular cycles with 27 kA/s up to 14 kA were achieved. The current leads withstood the test voltage of 3kV between two leads and between lead and ground. The one stream helium flow is regulated by the temperature at the warm end of the HTS to be 50K. The reliability of the first pair, especially of the cold terminal, is a clear go for the series of HTS current leads needed for the Series Test Facility, the String Test and the SIS100 ring. There is a separate 50K helium gas supply which allows a significant reduction of cooling requirements. These 19 pairs in total shall have a common design which will be slightly different to that of the first pair for the Prototype Test Facility.

Modeling Degradation of Polymer Electrolyte Fuel Cells

Mitigation strategies and/or advanced materials are needed to meet the stringent durability targets for polymer electrolyte fuel cells (PEFC) for transport applications [1]. Development of these strategies requires an improved understanding of the degradation mechanisms for electrocatalysts, catalyst supports, ionomer in catalyst layers, polymer membrane electrolyte, gas diffusion layers (GDL), bipolar plates, and seals. Although platinum is widely used as an electrocatalyst in low-temperature fuel cells because of its high activity for the oxygen reduction reaction (ORR) and its stability at cathode operating potentials, Pt can dissolve in acidic media. The dissolution rate increases at higher potentials and can accelerate under potentiodynamic conditions [1]. Dissolution of nano-Pt, highly dispersed on carbon support, was measured in 0.57 M HCLO4aqueous media using ICP-MS [2]. A solid solution theory was formulated to explain the observed peak in dissolved Pt concentration at ~1.1 V on the basis of enhanced dissolution at high potentials coupled with the protective oxide formation that stabilizes Pt by reducing its activity in the solid solution [3]. The observed growth in Pt particles and the resulting electrochemical surface area (ECSA) loss under cyclic potentials was analyzed using a model that determines the dynamics of particle size evolution due to dissolution of Pt catalyst into the electrolyte, redeposition of Pt from the electrolyte onto the Pt particles, and sintering of Pt particles. The simulation results suggest that the observed coarsening in size of Pt particles is primarily due to coalescence/sintering mechanism rather than Ostwald ripening [4].Carbon corrosion has been investigated in membrane electrode assemblies fabricated with varying degrees of graphitization [5]. The rate of carbon oxidation to CO2 was monitored by non-dispersive infrared spectroscopy (NDIR) at different temperatures, relative humidities, potentials and sweep rates. As observed by others [6], the measured CO2 emission rates had characteristic profiles showing multiple peaks and hysteresis under triangular potential cycles with variable lower potential limits (0.1-1.0 V), upper potential limits (0.6-1.3 V), and scan rates (2-50 mV.s-1). The observed profiles are consistent with a dynamic corrosion model that considers four electrochemical reactions for peroxide attack at low potentials, reversible formation of active surface oxides, conversion of active oxides to CO2, and reversible formation of passive oxides. Same model with different rate constants can describe the corrosion data for different carbon supports except that two-types of sites must be considered for Vulcan XC-72 (V-Type) and only one type of sites for high surface area Ketjenblack (E-Type) and graphitized KB (EA-Type). Preliminary work has been performed to extend the Pt growth model to include Pt coalescence that occurs as carbon corrodes, and the cathode catalyst layer (CCL) compacts due to collapse of pores and changes in carbon structure. Figure 1 presents empirical correlations that have been developed for Pt growth factor and Pt stratification factor. The first factor accounts for the effect of Pt dissolution and redeposition, and the second factor accounts for partial loss of three-phase boundary due to carbon corrosion. The product of the two factors gives Pt utilization, defined as the ratio of ECSA to geometric surface area calculated from the modeled evolution of Pt size distribution. Combined experimental and theoretical work shows that the loss in ECSA due to Pt dissolution results in performance degradation not only due to increased ORR kinetic overpotentials but also higher mass transfer overpotentials. In catalyst layers with low Pt loadings, increase in mass transfer overpotentials with ageing can greatly exceed the increase in kinetic overpotentials. Also, much of the increase in mass transfer overpotentials results from the greater resistance to O2 diffusion in the CCL ionomer [7].

Electrochemical Test Procedures for Accelerated Evaluation of Fuel Cell Cathode Catalyst Degradation

AbstractThe paper introduces an accelerated test procedure that was developed to evaluate the cathode catalyst stability. It is based on systematic analysis of square wave cycles (SWC) in comparison to triangular wave cycles (TWC). Two voltage windows were used: (i) 0.6–0.9 V to simulate the fuel cell drive cycles and (ii) 0.6–1.2 V to accelerate the test. When simulating the drive cycles over 6,000 h, an estimated loss of 40% in electrochemical surface area (ECSA) is found. Increasing the potential window, the testing time could be reduced to 20 h for TWC and for SWC to 4 h.

Investigation of HTS Current Leads Under Pulsed Operation for JT-60SA

The test of two Wendelstein 7-X (W7-X) prototype high temperature superconductor (HTS) current leads (CL) was extended to dynamic operation, in order to evaluate AC losses in parts of the CL. Trapezoidal and triangular current cycles up to a maximum current of 20 kA with different ramp rates between 0.5 kA/s and 10 kA/s were performed. Temperature changes at the warm end of the HTS-module and the influence on the heat load at the cold end of the CL were studied. Additionally, a DC operation that generates a power loss equivalent to the triangular pulsing run was investigated. AC losses in the low temperature part of the CL are estimated by simplified models and compared to the experimental results of the heat load measurements. The effect of the AC losses on the CL performance is discussed.

The Cold Test of Super-FRS Superconducting Dipole Prototype for FAIR Project

Superconducting dipole prototype of the Super-FRS (Super FRagment Separator) for FAIR Project (Facility for antiproton and Ion Research) which is jointly developed by the Institute of Modern Physics (Lanzhou), the Institute of Plasma Physics (Hefei) and the Institute of Electrical Engineering (Beijing), have passed the final magnetic field measurement and low temperature test. The magnetic flux density is up to 1.6 T when the operating current is 232 A, and magnetic field homogeneity meets the calculation result which is ±1 × 10-4. The single ramping tests up to 232 A and 278 A at the rate of 3 A/s, 3 triangular cycles ramping up to 232 A within 120 seconds, and the quench tests at 232 A and 278 A by using the spot heater were done. Some other tests were finished at the same time. All the test results indicate that the superconducting dipole prototype could meet the requirements of FAIR.

Iron-Catalyzed Cyclopropanation in 6 M KOH with in Situ Generation of Diazomethane

Diazomethane is a common and versatile reagent in organic synthesis whose broader use is generally impeded by its explosiveness and toxicity. Here we report that a simple iron porphyrin complex catalyzes the cyclopropanation of styrenes, enynes, and dienes under the demanding conditions [aqueous 6 molar potassium hydroxide (KOH) solution, open to air] necessary for the in situ generation of diazomethane from a water-soluble diazald derivative. A biphasic reaction medium arising from the immiscibility of the olefin substrates with water appears essential to the overall efficiency of the process. The work we describe highlights an approach to catalysis with untoward reactive intermediates, in which the conditions for their generation under operationally safe regimes dictate catalyst selection.

Optimal Identifying Codes in Cycles and Paths

The concept of identifying codes in a graph was introduced by Karpovsky et al. (in IEEE Trans Inf Theory 44(2):599–611, 1998). These codes have been studied in several types of graphs such as hypercubes, trees, the square grid, the triangular grid, cycles and paths. In this paper, we determine the optimal cardinalities of identifying codes in cycles and paths in the remaining open cases.

Isothermal and Thermal Fatigue of Tool Steel AISI H11

Lifetime of hot-work tool steels is often limited by the development of crack nets as a consequence of thermal or mechanical fatigue loading. In this paper, the isothermal and thermal fatigue behaviour of tool steel AISI H11 (German grade X38CrMoV 5-1) in the temperature range between room temperature and 650°C is investigated. In addition to stress controlled isothermal tension-compression fatigue tests, out-of-phase thermal fatigue tests were carried out using a servohydraulic testing system, keeping the macroscopic total strain of the gauge length constant, while triangular time-temperature cycles were applied. The temperature range was chosen in such a way that numbers of cycles to fracture between 1,000 and 10,000 were achieved. The development of stress amplitudes, plastic strain amplitudes as well as of mean stresses was analysed during the tests. Results of isothermal and thermal fatigue tests are compared and discussed.

06/01305 The analysis of triangular cycles of cooling and heating: Rozhentsev, A. et al. Applied Thermal Engineering, 2005, 25, (1), 21–30

06/01305 The analysis of triangular cycles of cooling and heating: Rozhentsev, A. et al. Applied Thermal Engineering, 2005, 25, (1), 21–30

Cutting Triangular Cycles of Lines in Space

We show that n lines in 3-space can be cut into O(n2-1/69log16/69n) pieces, such that all depth cycles defined by triples of lines are eliminated. This partially resolves a long-standing open problem in computational geometry, motivated by hidden-surface removal in computer graphics.

The analysis of triangular cycles of cooling and heating

Theoretical study of triangular cycle with cooling and heating at variable temperatures is investigated in this study. Simple approximated correlations for COP are obtained. By implementation of the cooling and heating using multistage machines, single-compressor machines accompanying with refrigerants mixtures, semiconductor thermopiles, and the supercritical cycles with variable temperature of heat rejection, the “triangular” cycle shows promising interesting features.