scholarly journals STUDY OF PHYSICAL PROCESSES IN THE DIRECT CURRENT LINK OF THE LOADING-BACK SCHEME OF ASYNCHRONOUS MACHINES

2020 ◽  
pp. 141-149
Author(s):  
Viktor V. Kharlamov ◽  
Denis I. Popov ◽  
Roman V. Sergeev
Keyword(s):  
Direct Current ◽  
Time Interval ◽  
Physical Processes ◽  
Asynchronous Machines ◽  
True Value ◽  
Power Of The Test ◽  
Asynchronous Motors ◽  
Procedural Error ◽  
Test Engine ◽  
Capacitor Capacitance

The article notes the tendency of introducing asynchronous engines, entailing the necessity to introduce the equipment which is intended to carry out maintenance, repair and acceptance check-outs. The general part of test circuits for asynchronous motors by the loading-back method with two controlled inverters is emphasized. The mathematical model of similar schemes’ functioning is shown. The article gives the results obtained by mathematic simulation of physical processes in the direct current link in the loading-back scheme for asynchronous machines Significant ripple voltage of constant voltage and DC in these circuits is noted. The issue of measuring power in the DC link passing through one inverter to the test engine and through another inverter from the load generator is considered. The authors carried out calculation of the capacities mentioned in the steady state modes for asynchronous machines with nominal power of 0.37 kW, 5.5 kW and 250 kW at different values of capacitor capacitance included in the DC link. Basing on the results of calculations, the authors found the dependence between the relative value of the procedural error in determining power in the DC link by the product of the current values of pulsed voltages and current. The current value from the product of instantaneous values of voltage and current at some time interval was taken as the true value of power. It is shown that at the capacitor capacity above some critical value this procedural error does not exceed 0.9% at the nominal power of the test engines 0.37 kW; 0.3% – at the power of 5.5 kW; 0.2% – at the power of 250 kW. This error increases dramatically when capacitor capacitance decreases. It is shown that the value of the capacitance corresponding to the inflection of the considered dependence approximately corresponds to the value necessary for limiting ripple voltage in the DC link of up to 600 V.

scholarly journals Effects of Transcranial Direct Current Stimulation on effort during a working-memory task

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
David Framorando ◽  
Tianlan Cai ◽  
Yi Wang ◽  
Alan J. Pegna
Keyword(s):  
Working Memory ◽  
Direct Current ◽  
Transcranial Direct Current Stimulation ◽  
Memory Task ◽  
Time Interval ◽  
Direct Current Stimulation ◽  
Anodal Stimulation ◽  
Dorsolateral Prefrontal ◽  
Systolic Time ◽  
Task Mastery

AbstractTranscranial Direct Current Stimulation (tDCS) has shown that stimulation of Dorsolateral Prefrontal Cortex (DLPFC) facilitates task performance in working-memory tasks. However, little is known about its potential effects on effort. This study examined whether tDCS affects effort during a working-memory task. Participants received anodal, cathodal and sham stimulation over DLPFC across three sessions before carrying out a 2-back task. During the task, effort-related cardiovascular measures were recorded—especially the Initial Systolic Time Interval (ISTI). Results showed that anodal stimulation produced a shorter ISTI, indicating a greater effort compared to cathodal and sham conditions, where effort was lower. These findings demonstrate that anodal stimulation helps participants to maintain engagement in a highly demanding task (by increasing task mastery), without which they would otherwise disengage. This study is the first to show that tDCS impacts the extent of effort engaged by individuals during a difficult task.

scholarly journals Are the Fractionation Corrections Correct: Are the Isotopic Shifts for 14C/12C Ratios in Physical Processes and Chemical Reactions Really Twice Those for 13C/12C?

Radiocarbon ◽  
2011 ◽  
Vol 53 (4) ◽  
pp. 691-704 ◽  
Author(s):  
John Southon
Keyword(s):  
Chemical Reactions ◽  
Isotopic Fractionation ◽  
Theoretical Work ◽  
Chemical Processes ◽  
Physical Processes ◽  
Isotopic Discrimination ◽  
True Value ◽  
A Value ◽  
Isotopic Shifts ◽  
Physical And Chemical

Conventional radiocarbon calculations correct for isotopic fractionation using an assumed value of 2.0 for the fractionation of 14C relative to 13C. In other words, isotopic discrimination in physical and chemical processes is assumed to cause relative shifts in 14C/12C ratios that are exactly double those of 13C/12C. This paper analyzes a 1984 experiment that produced a value for the fractionation ratio in photosynthesis of 2.3, which is used to this day by some researchers in the fields of hydrology and speleothem geochemistry. While the value of 2.3 is almost certainly incorrect, theoretical work suggests that the true value may indeed deviate from 2.0, which would have significant implications for 14C calculations.

Detection of Molecular Relapse of AML by Very Frequent Quantitative Monitoring of Different Molecular Markers (Fusion Transcripts and WT1) in Different Compartments (Peripheral Blood-PB, Bone Marrow-BM, and Selected CD34+ Bone Marrow Cells) and Its Treatment with Chemotherapy or Gemtuzumab Ozogamicin.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 4481-4481
Author(s):  
Jiri Mayer ◽  
Ivo Palasek ◽  
Zdenek Pospisil ◽  
Sona Struncova ◽  
Dana Dvorakova ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Residual Disease ◽  
Subsequent Development ◽  
Fusion Transcript ◽  
Gemtuzumab Ozogamicin ◽  
Time Interval ◽  
Clinical Relapse ◽  
Fusion Transcripts ◽  
True Value

Abstract Patients and Methods. In order to find some markers, which reliably enable to predict clinical relapse in AML patients, we primarily focused on patients with the known fusion transcript (CBFB-MYH, AML1-ETO, or involving the MLL gene) and correlated this values with the WT1 for estimation of the true value of WT1 monitoring of disease behavior in a given patients. The value of different compartments for minimal residual disease (MDR) monitoring (PB, BM or CD34+ BM cells) was also analyzed. The study was prospective; in the case of MDR dynamics, the patients were actively called for earlier visit. This strategy could estimate the real time interval from MRD level increase to hematological relapse detection. In the interventional part of the study, the patients with already known MRD dynamics were treated at the time of molecular relapse. Results and Discussion. In 67 AML patients and 3 healthy volunteers, 2184 BM or PB samples were examined, including 240 samples from CD34+ BM cells. Follow-up was 31–252 weeks (median: 88 w). The correlation between the fusion transcripts levels in BM and PB was excellent (r=0.9676). The correlation between WT1 PB and BM levels was far less satisfactory. Since the WT1 values were frequently >0 even if the level of fusion transcript =0, we wanted to find some “normal” value for WT1. Using the ROC curves, however, we were not able to find any WT1 level being a confidential marker of molecular remission in either compartment (PB, BM or CD34+). Molecular relapse was defined as a reappearance of the fusion transcript detection or its 10-fold increase, repeatedly detected. The time from molecular to hematological relapse was 8–79 days (median: 25 d). In the cases of subsequent development of hematological relapses, the levels of fusion transcript in CD34+ BM cells were one order of magnitude higher than in the BM or PB, even in the case of CD34− blasts. Eight patients were treated for 13 molecular relapses with following results: chemotherapy, CR=2, PR=2; gemtuzumab ozogamicin, CR=3, PR=1, NR=3; IL-2±DLI, CR=2 (PR was defined as a decrease in fusion transcript level at least 10-fold). Patients with CD33− blast at diagnosis did not respond to gemtuzumab ozogamicin. Non-responsiveness to one treatment option did not mean non-responsiveness to another treatment. Conclusion: Fusion transcript monitoring enables reliable detection of molecular relapse in AML and high values in CD34+ BM cells signalize imminent hematological relapse (even in the case of CD34− blasts). PB is a suitable compartment for frequent monitoring. However, in some cases, relapse are fulminate, hardly allowing any intervention. WT1 does not seem to be a reliable marker for exact molecular relapse detection. AML at the stage of molecular relapse behaves similarly to AML at the frank hematological relapse: there are CRs, PRs, or NRs when using chemotherapy or gemtuzumab ozogamicin. AML with CD33− blasts at diagnosis does not seem to respond to gemtuzumab ozogamicin at the stage of molecular relapse. Success of AML therapy in the future seems to be dependant on efficient targeting the leukemia stem cell.

scholarly journals Degradation of stator insulation of high-voltage asynchronous machines in gamma and neutron radiation field

2019 ◽  
Vol 34 (3) ◽  
pp. 264-271 ◽  
Author(s):  
Nenad Kartalovic ◽  
Bojan Jokanovic ◽  
Milan Bebic ◽  
Djordje Lazarevic
Keyword(s):  
Gamma Radiation ◽  
High Voltage ◽  
Power Plants ◽  
Asynchronous Motor ◽  
Life Time ◽  
Neutron Radiation ◽  
Time Duration ◽  
Asynchronous Machines ◽  
Asynchronous Motors ◽  
Time Exponent

This paper presents the results of an examination of function stability of high-voltage asynchronous motors exposed to ambient strain caused by combined neutron and gamma radiation. This problem appears in practice when a high-voltage asynchronous motor is used in nu- clear power plants where it can be exposed to this type of ambient strain. The failure of the engine's operation under such conditions may have unexpected consequences. As more than 50 % of failure (malfunction) of high-voltage asynchronous motors is caused by damage to stator insulation, the focus of the paper was on testing the effects of combined neutron and gamma radiation on stator insulation. The tests were carried out under well-controlled laboratory conditions on samples taken from both new and used factory coil windings. Two-layer samples were used to record partial discharge threshold voltage and breakdown voltage. By comparing the experimentally obtained results with the applicable mathematical-statistical procedure, an estimate was made of the aging acceleration of stator insulation and the time duration of reliable operation of high-voltage asynchronous motor was determined by life-time exponent.

scholarly journals On the Abyssal Circulation in the Glacial Atlantic

2008 ◽  
Vol 38 (9) ◽  
pp. 2014-2037 ◽  
Author(s):  
Olivier Marchal ◽  
William B. Curry
Keyword(s):  
Ocean Circulation ◽  
Benthic Foraminifera ◽  
Dissolved Inorganic Carbon ◽  
World Ocean ◽  
Volume Transport ◽  
Time Interval ◽  
Organic C ◽  
Power Of The Test ◽  
Abyssal Circulation ◽  
Sediment Data

Abstract An inverse method is used to evaluate the information contained in sediment data for the Atlantic basin during the Last Glacial Maximum (defined here as the time interval 18–21 kyr before present). The data being considered are an updated compilation of the isotopic ratios 18O/16O (δ18O) and 13C/12C (δ13C) of fossil shells of benthic foraminifera (bottom-dwelling organisms). First, an estimate of the abyssal circulation in the modern Atlantic is obtained, which is consistent with (i) climatologies of temperature and salinity of the World Ocean Circulation Experiment, (ii) observational estimates of volume transport at specific locations, and (iii) the statements of a finite-difference geostrophic model. Second, estimates of water properties (δ18O of equilibrium calcite or δ18Oc and δ13C of dissolved inorganic carbon or δ13CDIC) derived from sediment data are combined with this circulation estimate to test their consistency with the modern flow. It is found that more than approximately 80% of water property estimates (δ18Oc or δ13CDIC) are compatible with the modern flow given their uncertainties. The consistency of glacial δ13CDIC estimates with the modern flow could be rejected after two assumptions are made: (i) the uncertainty in these estimates is ±0.1‰ (this uncertainty includes errors in sediment core chronology and oceanic representativity of benthic δ13C, which alone appears better than this value on average); and (ii) δ13CDIC in the glacial deep Atlantic was dominated by a balance between water advection and organic C remineralization. Measurements of δ13C on benthic foraminifera are clearly useful, but the current uncertainties in the distribution and budget of δ13CDIC in the glacial Atlantic must be reduced to increase the power of the test.

The transient electromagnetic response of a magnetic or superparamagnetic ground

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 854-860 ◽  
Author(s):  
T. Lee
Keyword(s):  
Transient Response ◽  
Direct Current ◽  
Free Space ◽  
Electromagnetic Response ◽  
Time Constants ◽  
True Value ◽  
Transient Electromagnetic ◽  
Current Value ◽  
The Wire ◽  
Weakly Magnetic

The effect of superparamagnetic minerals on the transient response of a uniform ground can be modeled by allowing the permeability of the ground μ to vary with frequency ω as [Formula: see text] Here [Formula: see text] and [Formula: see text] are the upper and lower time constants for the superparamagnetic minerals and [Formula: see text] is the direct current value of the susceptibility. For single‐loop data it is found that the voltage will decay as 1/t, provided that [Formula: see text] and [Formula: see text] Here, a is the radius of the wire loop and b is the radius of the wire, t represents time and [Formula: see text] is the permeability of free space. Even if a separate transmitter and receiver are used, the transient will still be anomalous. For this case the 1/t term in the equations is less important, and more prevalent now is the [Formula: see text] term. These results show that a uniform ground behaves in a similar way to a ground which only has a thin superparamagnetic layer. A difference is that whereas the amplitude of the 1/t term could be drastically reduced by using a separate receiver, this is not the case for a uniform ground. A magnetic ground for late times will decay as [Formula: see text]. However, if the conductivity of the ground is estimated from apparent conductivities it will be found that the value of the conductivity will be incorrect by a factor that is related to the susceptibility [Formula: see text] of the ground. For a weakly magnetic ground the estimated conductivity [Formula: see text] is related to the true value of the conductivity [Formula: see text].

scholarly journals Effect of Caribbean Water Incursion into the Gulf of Mexico derived from Absolute Dynamic Topography, Satellite Data, and Remotely – sensed Chlorophyll-<i>a</i>

2019 ◽  
Author(s):  
Juan Antonio Delgado ◽  
Joël Sudre ◽  
Sorayda Tanahara ◽  
Ivonne Montes ◽  
José Martin Hernandez-Ayon ◽  
...  
Keyword(s):  
Satellite Data ◽  
Winter Period ◽  
Time Interval ◽  
Loop Current ◽  
Dynamic Topography ◽  
Physical Processes ◽  
Surface Layers ◽  
Chl A ◽  
Mean Differences ◽  
Oceanic Currents

Abstract. The dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCE’s) dominate the Gulf of Mexico's (GoM) surface layers' circulation transporting Caribbean water (CW) into the GoM.  In this work, 25-years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll-a (Chl-a) concentrations from 1998–2017 including temporal changes, mean differences, and regional concentration tendencies. Physical variables analyzed are absolute dynamic topography (ADT), oceanic currents, and wind stress. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of the CW with an inward incursion that starts in spring, peaks in the summer (reaching to 26.58˚N and 88.32˚W) and then retreats in winter. Minimum surface Chl-a concentrations (<0.08 mg m−3) are found during the summer-autumn period inside the region of maximum incursion of the CW; the opposite is observed during the winter period when the Chl-a concentrations were at a maximum, e.g., >0.14 mg m−3. The three-year running averages of ADT 40-cm isoline reproduce qualitatively the climatological pattern of 25 years showing that before 2002 the CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from Caribbean Sea have invaded the western GoM and reduced mean surface Chl-a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that, in the latter time interval, Chl-a concentration over waters deeper than 250 m has decreased significantly.

scholarly journals The History and Evolution of Optically Accessible Research Engines and Their Impact on Our Understanding of Engine Combustion

2014 ◽  
Author(s):  
Paul C. Miles
Keyword(s):  
High Speed ◽  
Combustion Process ◽  
Physical Processes ◽  
Engine Simulation ◽  
Engine Combustion ◽  
Test Engine ◽  
And Performance ◽  
Combustion Processes ◽  
Fundamental Physical

The development and application of optically accessible engines to further our understanding of in-cylinder combustion processes is reviewed, spanning early efforts in simplified engines to the more recent development of high-pressure, high-speed engines that retain the geometric complexities of modern production engines. Limitations of these engines with respect to the reproduction of realistic metal test engine characteristics and performance are identified, as well as methods that have been used to overcome these limitations. Lastly, the role of the work performed in these engines on clarifying the fundamental physical processes governing the combustion process and on laying the foundation for predictive engine simulation is summarized.

scholarly journals Influence of strands transposition on current distribution and power losses in windings of AC machines

2018 ◽  
Vol 12 (2) ◽  
pp. 86-92
Author(s):  
Branko Tomičić ◽  
Dunja Srpak
Keyword(s):  
Current Distribution ◽  
Motor Power ◽  
Power Losses ◽  
Ac Machines ◽  
Positive Effects ◽  
Asynchronous Machines ◽  
Asynchronous Motors ◽  
Different Types ◽  
Positive Effect ◽  
Small Positive Effect

This paper analyses how the type of winding affects the current distribution and power losses in armature winding. Using finite element method, four different types of winding used in large asynchronous motors are analyzed: form-wound concentric, with and without transposition, and form-wound barrel, with and without transposition, for the stationary state. In two cases, the calculation shows clear differences between maximum currents in strands, a shift in their phases, and a resulting increase of AC resistance. In two other cases, minor deviations, smaller phase shift and smaller increase of AC resistance, are detected. It indicates that in certain types of armature winding of large motors the strands transposition leads to significant positive effects in terms of motor power, while in other cases it leads to unnecessary complications making the manufacture of large asynchronous machines more difficult, with relatively small positive effect on the motor power losses.

Sign in / Sign up

Export Citation Format

Share Document