Abrupt Change In Slope Research Articles

Formation of Ti3SiC2 interphase coating on SiCf/SiC composite by electrophoretic deposition

AbstractTo improve the oxidation resistance of SiC composites at high temperature, the feasibility of using Ti3SiC2 coated via electrophoretic deposition (EPD) as a SiC fiber reinforced SiC composite interphase material was studied. Through fiber pullout, Ti3SiC2, due to its lamellar structure, has the possibility of improving the fracture toughness of SiCf/SiC composites. In this study, Ti3SiC2 coating was produced by EPD on SiC fiber; using Ti3SiC2‐coated SiC fabric, SiCf/SiC composite was fabricated by hot pressing. Platelet Ti3SiC2 powder pulverized into nanoparticles through high‐energy wet ball milling was uniformly coated on the SiC fiber in a direction in which the basal plane of the particles was parallel to the fiber. In a 3‐point bending test of the SiCf/SiC composite using Ti3SiC2‐coated SiC fabric, the SiCf/SiC composite exhibited brittle fracture behavior, but an abrupt slope change in the strength‐displacement curve was observed during loading due to the Ti3SiC2 interphase. On the fracture surface, delamination between each layer of SiC fabric was observed.

Observation of temperature-dependent kinetics for catalytic CO oxidation over TiO2-supported Pt catalysts

TiO2-supported Pt catalysts were prepared for the study of CO oxidation kinetics at reaction conditions of pressures (1–100Torr) and temperatures (300–500K). We find two distinct temperature ranges with different reaction kinetics distinguished by an abrupt slope change at around 380K in the Arrhenius plot only with the excess O2, not with the stoichiometric O2/CO ratio. We propose that Pt oxides are formed during the catalytic reactions with increasing temperatures under the oxidizing condition and the origin of the slope change is due to the changes in the reaction pathways of CO oxidation due to the Pt oxide formation.

Role of the rare earth in lattice and magnetic coupling in multiferroic h−HoMnO3

We used Raman scattering to study the lattice and magnetic excitations in the hexagonal HoMnO3 single crystals. The E2 phonon mode at 237 cm-1 is affected by the magnetic order. This mode is related to the displacement of Mn and O ions in a-b plane and modulates the Mn-O-Mn bond angles in a-b plane and the in-plane Mn-Mn superexchange interaction. The mode at 269 cm-1 associated to the displacement of the apical Ho3+ ions along the c direction presents an abrupt change of slope at TN showing that the role of the rare earth ions can not be neglected in the magnetic transition. We have identified magnon and crystal field excitations. The temperature dependence of the magnetic excitations has been compared to the Mn and Ho moment and indicates that the exchange interaction pattern between Mn and Ho atoms drives the uniaxial anisotropy gap above the Mn-spin-rotation transition.

Effect of CuO addition on crystallization and thermal expansion properties of Li2O–ZnO–SiO2 glass-ceramics

A Li2O-ZnO-SiO2 (LZS) glass system was modified with CuO, and its phase development, microstructure evolution, crystallization kinetics and thermal expansion properties were investigated as a function of heat treatment temperature. As a result of the X-ray diffraction study and microstructure observation, lithium zinc silicate formed as the first crystalline phase with increasing heat treatment temperature. Silica polymorph developed as minor crystalline phase at higher temperatures. From the X-ray diffraction patterns, CuO addition led to a decrease in both the crystallization temperature of lithium zinc silicate phase and the volume fraction of quartz phase. According to the crystallization kinetics, the crystallization activation energy for lithium zinc silicates is almost equal to the diffusion activation energy of Zn2+ in glass, it suggests that the diffusion of network modifier Zn2+ dominates the crystallization of lithium zinc silicates. Additionally, CuO addition caused the transition of Zn2+ from network modifiers to network formers. From the thermal expansion coefficient measurements, two abrupt changes in slope of the thermal expansion curves were observed and attributed to the phase transitions of cristobalite and lithium zinc silicate, respectively. Comparison of the thermal expansion coefficient of two types of glass-ceramics revealed that CuO addition in the LZS system can partly inhibit the formation of cristobalite at high temperatures.

Effect of an abrupt slope change on air entrainment and flow depths at stepped spillways

ABSTRACTSeveral stepped spillways have been built in recent decades, mostly integrated in the downstream faces of roller compacted concrete dams. Among them, only a few have changing bottom slopes. Comprehensive information on the effect of a slope change on the flow features is lacking. This paper reports a systematic study of air entrainment and flow bulking in skimming flow along stepped spillways in the vicinity of abrupt slope changes. Physical modelling was conducted using a large facility with abrupt pseudo-bottom slope changes from 50° to 30° and from 50° to 18.6°. Air–water flow measurements were conducted at several flow cross-sections upstream and downstream of the slope change. The results indicate a significant influence of the slope change on the air pattern and flow bulking. Four main flow sub-regions were identified to describe the typical air–water flow patterns. The normalized length of the influence reach induced by the slope change was found to depend mainly on the critical flow depth, regardless of the slope change and step height.

Analysis of the behavior of three digital elevation model correction methods on critical natural scenarios

Abstract Study region The methods explored in this study were tested in two study areas: Italy and Cuba. Study focus Virtually all Digital Elevation Models (DEM) contain flat areas or depression pixels that may be artifacts or actual landscape representations. These features must be removed before any further hydrological application can proceed. Diverse algorithms have been developed for the purpose of correcting these aspects, differing in how they handle the nature of the depressions, as well as the adopted mathematical procedures. In the present work, the behavior of a standard ( Fill ) and two advanced ( TOPAZ and PEM4PIT ) DEM correction methods on three critical natural scenarios is analyzed. Extensive flat areas, abrupt slope changes and large depressions − expressed in terms of: (1) geomorphological changes (elevation, affected area and slope); (2) flow velocity; (3) river network and width functions (WF) − are affected. New hydrological insights for the region Results confirm improved performance of the advanced methods over the standard method for each case study in Italy and Cuba. The analyzed parameters also show that correction processes are strongly influenced by the relief, the size of the predominating depressions and the neighbouring depressions. There is no one method among those compared which works optimally for every type of correction, and given that the majority of basins have diverse topographical conditions, a different approach to the corrections process and its computational procedures is likely needed.

Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

We study the temperature dependent magnetization properties of (010)-oriented Ni-Mn-Ga epitaxial films on MgO(001) substrates. In the martensitic phase, we observe pronounced abrupt slope changes in the magnetization loops for all studied samples. Our experimental findings are discussed in conjunction with the micromagnetic simulations, revealing that the characteristic magnetization behavior is governed solely by the magnetization switching within the specific martensitic variant pattern, and no reorientation of twin variants is involved in the process. Our study emphasizes the important role of the magnetostatic interactions in the magnetization behavior of magnetic shape memory alloy thin films.

Photoluminescence study of LiNbO3:Cr3+; W4+ at high pressure. Pressure dependence of spectroscopic parameters and local structure of Cr3+

In this study, the photoluminescence properties of congruent codoped LiNbO3:Cr3+; W4+, crystals have been systematically investigated by performing photoluminescence studies at room temperature in the 0–280 kbar pressure range. In particular, we focus on the influence that hydrostatic pressure has on the 2E→ 4A2 (R-lines) transitions of Cr3+. It has been observed that the pressure dependence of the spectral position of the R-lines associated with both Cr3+ centres β and γ shows a bilinear behaviour with an abrupt slope change near 210 kbar. This change is related to the existence of a pressure-induced structural phase transition in the LiNbO3 host. The analysis of experimental results provides the Racah parameters B and C and the crystal field parameter 10Dq and their pressure and volume, through the crystal field theory and equation of state, dependences.

Periodicity analysis of δ18O in precipitation over Central Europe: Time–frequency considerations of the isotopic ‘temperature’ effect

Summary In this paper the periodic patterns of the isotopic composition of precipitation (δ 18 O) for 22 stations located around Central Europe are investigated through sinusoidal models and wavelet analysis over a 23 years period (1980/01–2002/12). The seasonal distribution of δ 18 O follows the temporal variability of air temperature providing seasonal amplitudes ranging from 0.94‰ to 4.47‰; the monthly isotopic maximum is observed in July. The isotopic amplitude reflects the geographical dependencies of the isotopic composition of precipitation providing higher values when moving inland. In order to describe the dominant oscillation modes included in δ 18 O time series, the Morlet Continuous Wavelet Transform is evaluated. The main periodicity is represented at 12-months (annual periodicity) where the wavelet power is mainly concentrated. Stations (i.e. Cuxhaven, Trier, etc.) with limited seasonal isotopic effect provide sparse wavelet power areas at the annual periodicity mode explaining the fact that precipitation has a complex isotopic fingerprint that cannot be examined solely by the seasonality effect. Since temperature is the main contributor of the isotopic variability in mid-latitudes, the isotope–temperature effect is also investigated. The isotope–temperature slope ranges from 0.11‰/°C to 0.47‰/°C with steeper values observed at the southernmost stations of the study area. Bivariate wavelet analysis is applied in order to determine the correlation and the slope of the δ 18 O – temperature relationship over the time–frequency plane. High coherencies are detected at the annual periodicity mode. The time–frequency slope is calculated at the annual periodicity mode ranging from 0.45‰/°C to 0.83‰/°C with higher values at stations that show a more distinguishable seasonal isotopic behavior. Generally the slope fluctuates around a mean value but in certain cases (sites with low seasonal effect) abrupt slope changes are derived and the slope becomes strongly unstable.

Dynamics of the 2008 earthquake-triggered Wenjiagou Creek rock avalanche, Qingping, Sichuan, China

The Wenjiagou Creek rock avalanche was triggered by the 2008 Wenchuan earthquake. It traveled 4.6km and left a granular deposit of 1.5×108m3 in Wenjiagou Creek valley. The dynamics of the rock avalanche were studied through field and laboratory investigations and remote sensing. The dynamic course was divided into three segments: (1) Failing — the original slope failed due to the huge earthquake ground accelerations acting on a rock mass weakened by severe karstification; (2) Falling — the rock mass experienced several drops due to abrupt changes in slope, and broke into granular debris during collisions with the ground and mountain flanks; and (3) Flow — the broken granular mass flowed approximately 3km down the valley of Wenjiagou Creek. The transport mechanism of the granular mass of debris was studied by analyzing the structure of the deposit and through ring-shear tests. A gully incised into the deposit by rainfall runoff and debris flows enabled the internal structure of the deposit to be examined and sampled. In cross-section, the exposed deposit was finest near the base, and gradually became coarser towards the surface (inverse grading); in longitudinal section, deposits near the base and on the surface both became finer with increasing travel distance. Near the base, the granular debris experienced the maximum normal and shear stresses, and fragmented into the finest grains. Both normal and shear stresses between the grains gradually decreased from near the base to the surface. Samples were sheared in a ring-shear apparatus to simulate the shearing within the granular debris. Shear resistance between grains was found to decrease as grains became finer due to pervasive fragmentation, which is one of the possible mechanisms by which the granular debris was able to travel a long distance at a high speed.

Fragmentation and boosting of rock falls and rock avalanches

Fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches. The occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth inclined terrain followed by a flat region (a geometry common to many landslides) is first studied numerically by means of a discrete element 2-D code in which blocks are subjected to mutual collisions and impact with the terrain. This numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes. We thus analyze this geometry of impact in two cases: low- and high-impact energy. In the first case, where recent experimental data are available, a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments, a highly probable scenario in rock avalanche dynamics. When the impact is so energetic to disintegrate the landslide, we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche. As a consequence, a net momentum gain (boost) results along the horizontal direction due to the terrain asymmetry. However, under normal field conditions, only when the slope angle is greater than 70° and fragmentation produces clasts of fairly uniform size, the momentum and runout distance are significantly enhanced. Allowing for a spectrum of fragment sizes and velocities, we find a relationship between the degree of fragmentation and the magnitude of the extra boost.

Single photon laser altimeter data processing, analysis and experimental validation

Spaceborne laser altimeters are common instruments on-board the rendezvous spacecraft. This manuscript deals with the altimeters using a single photon approach, which belongs to the family of time-of-flight range measurements. Moreover, the single photon receiver part of the altimeter may be utilized as an Earth-to-spacecraft link enabling one-way ranging, time transfer and data transfer. The single photon altimeters evaluate actual altitude through the repetitive detections of single photons of the reflected laser pulses. We propose the single photon altimeter signal processing and data mining algorithm based on the Poisson statistic filter (histogram method) and the modified Kalman filter, providing all common altimetry products (altitude, slope, background photon flux and albedo). The Kalman filter is extended for the background noise filtering, the varying slope adaptation and the non-causal extension for an abrupt slope change. Moreover, the algorithm partially removes the major drawback of a single photon altitude reading, namely that the photon detection measurement statistics must be gathered. The developed algorithm deduces the actual altitude on the basis of a single photon detection; thus, being optimal in the sense that each detected signal photon carrying altitude information is tracked and no altitude information is lost. The algorithm was tested on the simulated datasets and partially cross-probed with the experimental data collected using the developed single photon altimeter breadboard based on the microchip laser with the pulse energy on the order of microjoule and the repetition rate of several kilohertz. We demonstrated that such an altimeter configuration may be utilized for landing or hovering a small body (asteroid, comet).

Active flexural‐slip faulting: A study from the Pamir‐Tian Shan convergent zone, NW China

AbstractThe flexural‐slip fault (FSF), a type of secondary fault generated by bed‐parallel slip, occurs commonly and plays an important role in accommodating fold growth. Although the kinematics and mechanics of FSFs are well studied, relatively few field observations or geometric models explore its geomorphic expression. In the Pamir‐Tian Shan convergent zone, NW China, suites of well‐preserved FSF scarps displace fluvial terraces in the Mingyaole and Wulagen folds. Integrating interpretations of Google Earth images, detailed geologic and geomorphic mapping, and differential GPS measurements of terrace surfaces, we summarize geomorphic features that typify these faults and create kinematic models of active flexural‐slip faulting. Our study indicates the following: (i) FSF scarps commonly occur near synclinal hinges, irrespective of whether (a) the dip direction of beds on either side of the hinge is unidirectional or in opposite directions, (b) the hinge is migrating or fixed, or (c) the hinge shape is narrow and angular or wide and curved. (ii) Active FSFs are likely to produce higher scarps on steeper beds, whereas lower or no topographic scarps typify gentler beds. (iii) Tilt angles of the terrace surface displaced above FSFs progressively decrease farther away from the hinge, with abrupt changes in slope coinciding with FSF scarps; the changes in tilt angle and scarp height have a predictable geometric relationship. (iv) Active FSFs can accommodate a significant fraction of total slip and play a significant role in folding deformation. (v) Active FSFs may be used to assess seismic hazards associated with active folds and associated blind thrusts.

A CORRELATED STUDY OF OPTICAL AND X-RAY AFTERGLOWS OF GRBs

We study an extensive sample of 87 GRBs for which there are well sampled and simultaneous optical and X-ray light-curves. We extract the cleanest possible signal of the afterglow component, and compare the temporal behaviors of the X-ray light-curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst. Overall we find 62\% GRBs that are consistent with the standard afterglow model. When more advanced modeling is invoked, up to 91\% of the bursts in our sample may be consistent with the external shock model. A large fraction of these bursts are consistent with occurring in a constant interstellar density medium (ISM) (61\%) while only 39\% of them occur in a wind-like medium. Only 9 cases have afterglow light-curves that exactly match the standard fireball model prediction, having a single power law decay in both energy bands which are observed during their entire duration. In particular, for the bursts with chromatic behavior additional model assumptions must be made over limited segments of the light-curves in order for these bursts to fully agree with the external shock model. Interestingly, for 54\% of the X-ray and 40\% of the optical band observations the end of the shallow decay ($t^{\sim-0.5}$) period coincides with the jet break ($t^{\sim-p}$) time, causing an abrupt change in decay slope. The fraction of the burst that consistent with the external shock model is independent of the observational epochs in the rest frame of GRBs. Moreover, no cases can be explained by the cooling frequency crossing the X-ray or optical band.

Depositional characteristics of debris flows in a rectangular channel with an abrupt change in slope

The degradation in the discharge capacity of culvert installed in mountain region is typically attributable to debris flow deposition, which may result in property damage and serious casualties. Understanding and accurately reproducing the behavior and the deposition features of debris flows with different material properties under various geometrical configurations are prerequisites for developing advanced design criteria for drainage culverts to prevent such damages. This study employed a series of laboratory experiments of debris flows in a rectangular channel with a constant width and with the change of slope to investigate the behavior of debris flows under a variety of conditions regarding approaching and culvert-like downstream channel slopes, representative grain sizes and sediment volume concentrations. The experimental results show that the thickness of debris flow can substantially increase (up to more than four times) compared to the thickness of clean water flow at the same flow rate. Sediment deposition of fine-material debris flow begins further downstream with an approximately 3° higher surface slope compared to the case of coarse-material debris flow. Thus, the deposition area of coarse-material debris flow reaches further upstream in the approaching channel than that of fine-material debris flow. The total volume of coarse-material debris flow deposition in the channel appears to be larger than that of fine-material debris flow deposition. Based on experimental measurements and a series of complementary numerical simulations, we have developed a logistic regression model with the goal of determining optimal design criteria to prevent debris flow from depositing in the culvert-like channel. The resulting estimated logistic regression coefficients and derived deposition criteria curve indicate that the deposition of debris flow in the culvert-like channel is controlled predominantly by the bottom slope as well as the sediment volume concentration, whereas debris flow deposition is relatively less sensitive to the approaching channel slope and the representative grain size.

Magnetic properties of Dirac fermions in a buckled honeycomb lattice

We calculate the magnetic response of a buckled honeycomb lattice with intrinsic spin-orbit coupling (such as silicene) which supports valley-spin polarized energy bands when subjected to a perpendicular electric field $E_z$. By changing the magnitude of the external electric field, the size of the two band gaps involved can be tuned, and a transition from a topological insulator (TI) to a trivial band insulator (BI) is induced as one of the gaps becomes zero, and the system enters a valley-spin polarized metallic state (VSPM). In an external magnetic field ($B$), a distinct signature of the transition is seen in the derivative of the magnetization with respect to chemical potential ($\mu$) which gives the quantization of the Hall plateaus through the Streda relation. When plotted as a function of the external electric field, the magnetization has an abrupt change in slope at its minimum which signals the VSPM state. The magnetic susceptibility ($\chi$) shows jumps as a function of $\mu$ when a band gap is crossed which provides a measure of the gaps' variation as a function of external electric field. Alternatively, at fixed $\mu$, the susceptibility displays an increasingly large diamagnetic response as the electric field approaches the critical value of the VSPM phase. In the VSPM state, magnetic oscillations exist for any value of chemical potential while for the TI, and BI state, $\mu$ must be larger than the minimum gap in the system. When $\mu$ is larger than both gaps, there are two fundamental cyclotron frequencies (which can also be tuned by $E_z$) involved in the de-Haas van-Alphen oscillations which are close in magnitude. This causes a prominent beating pattern to emerge.

Assessing sensor accuracy for non-adjunct use of continuous glucose monitoring.

The level of continuous glucose monitoring (CGM) accuracy needed for insulin dosing using sensor values (i.e., the level of accuracy permitting non-adjunct CGM use) is a topic of ongoing debate. Assessment of this level in clinical experiments is virtually impossible because the magnitude of CGM errors cannot be manipulated and related prospectively to clinical outcomes. A combination of archival data (parallel CGM, insulin pump, self-monitoring of blood glucose [SMBG] records, and meals for 56 pump users with type 1 diabetes) and in silico experiments was used to "replay" real-life treatment scenarios and relate sensor error to glycemic outcomes. Nominal blood glucose (BG) traces were extracted using a mathematical model, yielding 2,082 BG segments each initiated by insulin bolus and confirmed by SMBG. These segments were replayed at seven sensor accuracy levels (mean absolute relative differences [MARDs] of 3-22%) testing six scenarios: insulin dosing using sensor values, threshold, and predictive alarms, each without or with considering CGM trend arrows. In all six scenarios, the occurrence of hypoglycemia (frequency of BG levels ≤50 mg/dL and BG levels ≤39 mg/dL) increased with sensor error, displaying an abrupt slope change at MARD =10%. Similarly, hyperglycemia (frequency of BG levels ≥250 mg/dL and BG levels ≥400 mg/dL) increased and displayed an abrupt slope change at MARD=10%. When added to insulin dosing decisions, information from CGM trend arrows, threshold, and predictive alarms resulted in improvement in average glycemia by 1.86, 8.17, and 8.88 mg/dL, respectively. Using CGM for insulin dosing decisions is feasible below a certain level of sensor error, estimated in silico at MARD=10%. In our experiments, further accuracy improvement did not contribute substantively to better glycemic outcomes.

Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen

The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time–temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling.In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time–temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4W/m2K and for nucleate-boiling h=1355±51W/m2K. These values were further validated by predicting the time–temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations.The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to improvements in the design of cooling devices in the cryobiology field.

Determination of critical micelle concentration of cationic surfactants by surface-enhanced Raman scattering

A novel approach, based on surface-enhanced Raman scattering (SERS) and 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) functionalized silver nanoparticles, was developed to determine the critical micelle concentration (CMC) of cationic surfactants. A graph was generated by plotting the Raman intensity ratio between the aromatic ring vibration of DTNB at 1558 cm−1 and its symmetric nitro stretching at 1333 cm−1 as a function of surfactant concentration. An abrupt change of slope at a particular concentration was shown to reliably predict the CMC of cetyltrimethylammonium bromide (CTAB).

Changes in shear wave splitting before the 2010 Eyjafjallajökull eruption in Iceland

SUMMARY We use shear wave splitting (SWS) above microearthquakes to monitor stress variations before the 2010 March and April flank and summit eruptions of Eyjafjallaj¨ okull volcano in Iceland. SWS time delays before Eyjafjallaj¨ okull show characteristic variations similar to those seen before earthquakes. The time delays display a nearly linear increase before the eruption, an abrupt change of slope and a rapid nearly linear decrease until the flank eruption begins. Similar variations before earthquakes are interpreted as stress-accumulation increases, and stress-relaxation decreases as microcracks coalesce onto the eventual fault plane. The changes in SWS before Eyjafjallaj¨ okull are interpreted as a similar stress-accumulation increase, as magma penetrates the crust, and stress-relaxation decrease as microcracks coalesce onto the magma conduit prior to magma release. We suggest that the remarkable similarity between stress changes before eruption and earthquake is strong evidence for the New Geophysics of a critically microcracked crust.