Small Tr Research Articles

Thresholds for triggering the propagation of meteorological drought to hydrological drought in water-limited regions of China

Propagation thresholds that trigger a transition between meteorological drought and hydrological drought are poorly understood, which hinders effective establishment of drought warning systems and prevention measures. Here, propagation thresholds were assessed by firstly identifying drought events during 1961–2016 in the Yellow River Basin, China, subsequently pooling, excluding, and matching them, and finally assessing their threshold conditions by using a combined Copula function and transition rate (Tr) analysis. These results show that response time changed according to variations in drought duration and watershed characteristics. Importantly, response times increased according to the timescales over which they were studied; for example, the Wenjiachuan watershed recorded response times of 8, 10, 10, and 13 months when examined at 1-, 3-, 6-, and 12-month timescales, respectively. Additionally, the severity and duration of meteorological and hydrological drought events both increased when events were combined rather than studied individually. These effects were also amplified for matched meteorological and hydrological droughts by factors of 1.67 (severity) and 1.45 (duration), respectively. Shorter response times were identified in the Linjiacun (LJC) and Zhangjiashan (ZJS) watersheds, and correlated with their relatively small Tr values of 43 % and 47 %, respectively. Higher propagation thresholds for drought characteristics (e.g., 1.81 and 1.95 for drought severity in the LJC and ZJS watersheds, respectively) imply that shorter response times tended to have greater effects on hydrological drought events and lowered their Tr, and vice versa. These results provide new insight into propagation thresholds used for water resource planning and management, and may help to mitigate the effects of future climate change.

MP3RAGE: Simultaneous mapping of T1 and in human brain at 7T.

To map T1 and the local flip angle ( ) in human brain using a single MP3RAGE sequence with 3 rapid acquisitions of gradient echoes (RAGEs). A third RAGE with a relatively high flip angle was appended to an MP2RAGE sequence. Through curve fitting and a rational approximation for small flip angles and short TR, closed form solutions for T1 and were derived. The influence of different k-space encoding schemes on precision and whether edge enhancement artifacts could be reduced with a saturation pulse applied prior to the third RAGE were explored. Validation of T1 estimates was performed using single-slice inversion recovery (IR) and a subsequent region-of-interest-based comparison, whereas validation of was performed using a whole brain pixelwise comparison to a DREAM flip angle mapping protocol. Lastly, MP3RAGE was compared to T1 -mapping by MP2RAGE with separate correction. Whole brain maps of T1 and at 1 mm isotropic resolution were obtained with MP3RAGE in 06:37 min. A linear-reverse centric-reverse centric phase-encoding order of the 3 RAGEs improved precision, and artifacts were successfully reduced with the saturation pulse. Estimations of T1 and deviated +2.5 ± 3.1% and -1.7 ± 8.6% from their respective references. T1 and can be mapped simultaneously using MP3RAGE. The approach can be thought of as combining MP2RAGE with a dual flip angle T1 -mapping protocol. Both maps can be solved for analytically and will be inherently co-registered at the high resolution associated with MPRAGE.

Hydrothermal Behavior of Transient Fluid Flow and Heat Transfer Through a Rotating Curved Rectangular Duct with Natural and Forced Convection

The present work explores a spectral-based computational study on hydrothermal behavior of transient fluid flow with natural and forced convective heat transfer through a rotating curved rectangular duct of strong curvature. The outer wall of the duct is heated while the inner wall cooled, the other walls being thermally insulated. The system rotates about the vertical axis in the positive and negative direction for the Taylor number (-1000≤Tr≤1000) with a constant non-dimensional pressure gradient force, the Dean number Dn = 2000. Time-history analysis is performed and fluid characteristics are well determined by depicting the phase space of the time-history result. It is found that the chaotic flow turns into steady-state flow through multi-periodic and periodic oscillating flows, if Tr is increased either in the positive or in the negative direction. Streamlines of secondary flow and isotherms are obtained at some specific values of Tr, and it is found that the time-dependent flow consists of asymmetric 2- to multi-vortex solutions. Vortex structure of secondary flows is obtained for physically realizable solutions and it is found that maximum 8-vortex is obtained for the chaotic solution while 2-vortex for the steady-state solution. Nusselt number as well as temperature gradient is calculated as an index of heat transfer, and it is found that convective heat transfer is significantly enhanced by the secondary flow; and the chaotic flow, which occurs relatively at small Tr, boosts heat transfer more effectively than the steady-state or other solutions. Finally, our numerical results have been validated with the experimental outcomes and it is found that there is a good agreement between the numerical and experimental investigations.

Electrostatically Driven Guest Binding in Self-Assembled Molecular Network of Hexagonal Pyridine Macrocycle at the Liquid/Solid Interface: Symmetry Breaking Induced by Coadsorbed Solvent Molecules.

We present here the construction of a self-assembled two-dimensional network at the liquid/solid interface using a hexagonal pyridine macrocycle which binds an organic cation in its intrinsic porous space by electrostatic interactions. For this purpose, a hexagonal pyridinylene-butadiynylene macrocycle (PyBM) having six octyloxymethyl groups, PyBM-C8, was synthesized. As guests, tropylium (Tr) tetrafluoroborate and trioxatriangulenium (TOTA) hexafluorophosphate were used. In this study, we focused on (i) the network patterns of PyBM-C8 which change in response to its concentration and (ii) the position of the guest immobilized in the porous space of the macrocycle. Scanning tunneling microscopy (STM) observations at the interface of 1,2,4-trichlorobenzene (TCB) and highly oriented pyrolytic graphite (HOPG) revealed that PyBM-C8 formed four different polymorphs, oblique, loose hexagonal, linear, and rectangular, depending on the solute concentration and annealing treatment. Solvent TCB molecules are likely coadsorbed to not only the intrinsically porous space of PyBM-C8 (internal TCB) but also the space outside of the macrocycle between its alkyl chains (external TCB) in most of the cases. Upon adding the guest cation, whereas small Tr was not visualized in the pore due to size mismatching, larger TOTA was clearly observed in each pore. In addition, based on high-resolution STM images of the rhombus packing pattern of PyBM-C8, we revealed experimentally that TOTA was placed at an off-center position of the deformed hexagonal macrocyclic core in the rhombus pattern. On the basis of the molecular mechanics calculations, we hypothesize that the off-center location of TOTA is due to deformation of the hexagonal macrocycle through interaction with two external TCB molecules located at opposite edges of the macrocyclic core. Symmetry breaking of the macrocyclic host framework induced by coadsorbed surrounding solvent molecules thus plays a significant role in host-guest complexation at the liquid/solid interface.

Correlation between SPGR MR signal intensity and iron concentration: Phantom study

Brain iron deposits have been demonstrated to be an important indicator in the pathophysiology of neurodegenerative processes. Hence, it is crucial to study the basic characteristics of ferric ion by using a noninvasive imaging modality, such as magnetic resonance imaging (MRI). Spoiled gradient recalled echo (SPGR) is one of the rapid MRI scanning pulse sequences and has been widely used in clinical diagnosis. There are three important scanning parameters, i.e., repetition time (TR), echo time (TE), and flip angle (FA), which will affect the SPGR MR signal intensity (SI) and contrast of investigated tissues and organs. The purpose of this study is to investigate the variability of SPGR MR SIs of ferric iron solutions with various concentrations by changing the TR, TE, and FA using a 1.5-T clinical whole body scanner. It was found that the optimal flip angle, i.e., the Ernst angle, increased with the concentration of ferric ions. The SI increased rapidly at smaller TRs and then rose slowly as the TR became larger. The SI was also found to be smaller for longer TE. Furthermore, there was better linearity between the MR, SI, and ferric iron concentration for the smaller TE, smaller TR, and larger FA.

A Comparative Study on Vortex Transmitter versus Differential Pressure Transmitter for Flow Control

This research emphasizes on the study of Vortex transmitter and Differential Pressure (DP) transmitter performance for a laboratory pilot plant by observing process response criteria consisting of dead-time (TD), rise time (TR), overshoot (%OS) and settling time (TS) for set point changes in a Proportional-Integral-Derivative (PID) flow control architecture. Four experiments were conducted; rising set point for Vortex transmitter, rising set point for DP transmitter, falling set point for Vortex transmitter and falling set point for DP transmitter. Limit tolerance test for Vortex transmitter and DP transmitter were done to determine the operational limits. Continuous Cycling Method is applied for controller tuning. Control and data collection for the flow plant is done using Distributed Control System (DCS) in real time. It is observed that Vortex transmitter produces a smaller TD, TS, Ts and %OS compared to DP transmitter for falling SP experiment, while less conclusive results were obtained for rising SP set up where Vortex transmitter produces a larger TD and Ts but smaller TR and %OS.

Assessment of logging efficiency and development of allometric models for predicting stumpage volume of some commercial tree species in Ghana

SUMMARY The need to develop instruments to capture the realistic stumpage volume and influence loggers to improve on their logging efficiency has been a topic of interest in recent times. This study assessed the logging efficiency in Ghana and developed allometric models to predict stumpage volume. A total of 135 trees from nine timber species were sampled from three logging sites during commercial logging operations. The average logging recovery for all sampled trees was about 75 %. The small-end diameter of the merchantable residues averaged between 31 cm and 60 cm while their length values varied from 3.0 m to 8.5 m. In general, species-specific models exhibited better predictive power than mixed-species models. Models that predicted total merchantable volume from the volume of the extracted logs had the best fits, with Furnival index values ranging from 0.590 to 1.727. Results of the models' validation indicated that mixed species models could predict merchantable volume better for relatively small tr...

Slice acquisition order and blood oxygenation level dependent frequency content: an event-related functional magnetic resonance imaging study.

Many event-related functional magnetic resonance imaging paradigms performed so far have been designed to study a limited part of the brain with high temporal resolution. However, event-related paradigms can be exploratory, therefore requiring whole brain scans and so repetition times (TR) of several seconds. For these large TR values, the slice acquisition order may have an important effect on the detection of event-related activation. Indeed, when the scanning is interleaved, the temporal delay between the acquisition of two contiguous slices can reach a few seconds. During this time, the subject is likely to move, and the haemodynamic response will vary significantly. In this case, the interpolation applied between contiguous slices for motion correction induces a temporal smoothing between voxels that are spatially close but temporally sampled a few seconds apart. This should modify the frequency structure of the response and may impair the detection of short events. We, therefore tested the effect of three acquisition schemes (sequential, sequential with gap and interleaved, INT) at two repetition times (TR=3 and 6 s on six and seven subjects, respectively) on activation detection and frequency content in a visual motion event-related paradigm. Unexpectedly, for large TR (6 s), results were found in favour of the INT acquisition scheme (P<0.05). For smaller TR, no strong bias could be found. Generally, intra-subject variability (across acquisition schemes) is found to be much smaller than inter-subject variability, confirming the importance of multi-subjects analyses. Our study also shows that important physiological information is carried by high frequency components that should not be filtered out.

Large angle spin-echo imaging

A study was undertaken to assess the use of excitation flip angles greater than 90 degrees for T1 weighted spin-echo (SE) imaging with a single 180 degrees refocusing pulse and short TR values. Theoretical predictions of signal intensity for SE images with excitation pulse angles of 90-180 degrees were calculated based on the Bloch equations and then measured experimentally from MR images of MnCl2 phantoms of various concentrations. Liver signal-to-noise ratios (SNR) and liver-spleen contrast-to-noise ratios (CNR) were measured from breathhold MR images of the upper abdomen in 16 patients using 90 and 110 degrees excitation flip angles. The theoretical predictions showed significant improvements in SNR with excitation flip angles > 90 degrees, which were more pronounced at small TR values. The phantom studies showed reasonably good agreement with the theoretical predictions in correlating the excitation pulse angle with signal intensity. In the human imaging studies, the 110 degrees excitation pulse angle resulted in a 7.4% (p < .01) increase in liver SNR and an 8.2% (p = .2) increase in liver-spleen CNR compared to the 90 degrees pulse angle at TR = 275 ms. Increased signal intensity resulting from the use of large flip angle excitation pulses with a single echo SE pulse sequence was predicted and confirmed experimentally in phantoms and humans.

Removal of influenza A virus, phage T1, and PP7 from fluids with a nylon 0.04‐μM membrane filter

AbstractWe tested the ability of a 0.04‐μm nylon membrane filter to remove viral agents (influenza A virus, 80–120 nm; phage T1, 50–150 nm; and phage PP7, 25 nm) from the following media: ultrapure water (UPW), Dulbecco's modified Eagle minimum essential medium (DMEM), gelatin phosphate (GP), DMEM with 10% (DMEM‐10) fetal bovine serum (FBS), and 100% FBS. When challenged with at least 3.0 × 107 plaque‐forming units/mL, no influenza A virus was detected downstream of the filter with any of the fluids tested. The titer reduction (Tr) was determined using the equation: equation image .Higher concentrations of phage T1 were removed from UPW (Tr = 1.6 × 106) and DMEM (Tr = 1.1 × 106) than from GP (Tr = 9.3 × 103), DMEM‐10 (Tr = 1.5 × 102), and 100% FBS (Tr = 2.4 × 102). Phage PP7 was removed in significant numbers only in ultrapure water (Tr = 8.5 × 104). The results indicate that adsorption enhanced the titer reduction in fluids containing low levels of protein. The titer reduction in DMEM‐10 and 100% FBS may reflect the sieving properties of the 0.04‐μm filter. As expected, a much smaller Tr was observed in the filtrate of the 0.2‐μm filters, compared to the 0.04 μm filters. In contrast to the 0.04‐μm filter, no increase in Tr was detected when the 0.2‐μm filters were challenged with virus diluted in UPW compared with virus diluted in GP. These results suggest that the 0.04‐μm filter has greater adsorptive properties than the 0.2‐μm filter. © 1994 by John Wiley &amp; Sons, Inc..

Effect of pressure rise time on starting transients of flue pipes

A special wind supply provides adjustable rise time Tr. Adjustable closed and open pipes having frequencies 198 to 256 Hz are studied. The steady‐state supply pressure is 530 Pa. The precursor, at several times the fundamental frequency, and a subsequent burst dominated by the next mode above the fundamental are strongest for Tr between 1 and 10 fundamental periods, but may vanish for larger or smaller Tr. For nearly harmonic pipe resonances, the fundamental and higher components can grow simultaneously, and the burst may exceed the steady‐state amplitude. For more inharmonic modes (e.g., a wider pipe) the fundamental quenches the burst when the overall amplitude is well below steady state. External sound at the fundamental frequency suppresses both the precursor and the subsequent burst. Important features of the experimental results occur in a computer model that involves time‐delayed nonlinear feedback and uses simple oscillators to represent resonator modes [N.H. Fletcher, Acustica 34, 224–233 (1976)]. With numerical rather than analytical solutions it is possible to treat the realistic case of the fully switched jet.

A modified saturation-recovery approximation for multiple spin-echo pulse sequences.

In equations describing multiple spin-echo pulse sequences, the T1 dependence is often approximated by a saturation-recovery expression, which is valid only when the repetition time TR is much greater than the time required for the echoes. A slight modification of this approximation greatly increases its accuracy for small TR values.

Some Results Concerning the OB Aggregate Around Eta Carinae

UBV observations of stars in the small and compact cluster Tr 15 located 20 arcmin north of Eta Carinae confirms its physical connection to the OB aggregate comprising TR 14, Tr 16 and Cr 228. Its corrected distance modulus is Vo–Mv = 12.1, with a mean interstellar absorption of Av = 1.4 ± 0.2 mag. Two very red variable stars, RT Car, close to the cluster (2 arcmin), and BO Car, about 8 arcmin southeast, appear to be related to the cluster itself. These two are the only bright red supergiants in the whole region, and from the RICK measures the probable membership of both is verified. The extinction law from the B-V, V-I diagram indicates a higher value of R in comparison with the normal one, but lower than the amount derived earlier for the Tr 14/16 (Feinstein, Marraco, and Muzzio 1973), and which is also confirmed with new measures in this photometric system. The extinction law for the young cluster NGC 6611 (Feinstein, in preparation) appears to be the same, in spite of being probably younger.