Blood oxygenation level dependent (BOLD). Renal imaging. Concepts and applications
Many renal diseases as well as several pharmacons cause a change in renal blood flow and/or renal oxygenation. The blood oxygenation level dependent (BOLD) imaging takes advantage of local field inhomogeneities and is based on a T2*-weighted sequence. BOLD is a non-invasive method allowing an estimation of the renal, particularly the medullary oxygenation, and an indirect measurement of blood flow without administration of contrast agents. Thus, effects of different drugs on the kidney and various renal diseases can be controlled and observed. This work will provide an overview of the studies carried out so far and identify ways how BOLD can be used in clinical studies. (orig.)
Nissen, Johanna C.; Haneder, Stefan; Schoenberg, Stefan O.; Michaely, Henrik J. [Heidelberg Univ. Medizinische Fakultaet Mannheim (Germany). Inst. fuer Klinische Radiologie und Nuklearmedizin; Mie, Moritz B.; Zoellner, Frank G. [Heidelberg Univ. Medizinische Fakultaet Mannheim (DE). Inst. fuer Computerunterstuetzte Klinische Medizin (CKM)
2010-07-01
Many renal diseases as well as several pharmacons cause a change in renal blood flow and/or renal oxygenation. The blood oxygenation level dependent (BOLD) imaging takes advantage of local field inhomogeneities and is based on a T2{sup *}-weighted sequence. BOLD is a non-invasive method allowing an estimation of the renal, particularly the medullary oxygenation, and an indirect measurement of blood flow without administration of contrast agents. Thus, effects of different drugs on the kidney and various renal diseases can be controlled and observed. This work will provide an overview of the studies carried out so far and identify ways how BOLD can be used in clinical studies. (orig.)
Blood oxygenation level-dependent MRI for assessment of renal oxygenation
Neugarten J; Golestaneh L
2014-01-01
Joel Neugarten, Ladan Golestaneh Renal Division, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA Abstract: Blood oxygen level-dependent magnetic resonance imaging (BOLD MRI) has recently emerged as an important noninvasive technique to assess intrarenal oxygenation under physiologic and pathophysiologic conditions. Although this tool represents a major addition to our armamentarium of methodologies to investigate the role of hypoxia in the pathogenesis of acute...
Tsurugizawa, Tomokazu; Uematsu, Akira; Uneyama, Hisayuki; Torii, Kunio
2009-12-01
The postingestive actions after intragastric or oronasal stimulation of fat have been well investigated. The blood oxygenation level-dependent (BOLD) signal changes, however, after intragastric load of corn oil emulsion have yet to be elucidated. Here, using functional magnetic resonance imaging, we investigated the BOLD signal response to gut corn oil emulsion in nonanesthetized rats. Intragastrically infused 7% corn oil emulsion induced a BOLD signal increase in several brain regions, including the bilateral amygdala, hippocampus and the ventral tegmental area. These results indicate that the limbic system responds to gut corn oil emulsion and that activation of this system could promote the reinforcing action for food with high fat content. PMID:19918206
Blood oxygenation level-dependent MRI for assessment of renal oxygenation
Neugarten J
2014-11-01
Full Text Available Joel Neugarten, Ladan Golestaneh Renal Division, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY, USA Abstract: Blood oxygen level-dependent magnetic resonance imaging (BOLD MRI has recently emerged as an important noninvasive technique to assess intrarenal oxygenation under physiologic and pathophysiologic conditions. Although this tool represents a major addition to our armamentarium of methodologies to investigate the role of hypoxia in the pathogenesis of acute kidney injury and progressive chronic kidney disease, numerous technical limitations confound interpretation of data derived from this approach. BOLD MRI has been utilized to assess intrarenal oxygenation in numerous experimental models of kidney disease and in human subjects with diabetic and nondiabetic chronic kidney disease, acute kidney injury, renal allograft rejection, contrast-associated nephropathy, and obstructive uropathy. However, confidence in conclusions based on data derived from BOLD MRI measurements will require continuing advances and technical refinements in the use of this technique. Keywords: kidney, hypoxia, oxygenation, diabetes mellitus, chronic kidney disease, acute kidney injury, contrast-associated nephropathy, BOLD MRI
Zhang, Qingtian; Hu, Xiaolin; Luo, Huan; Li, Jianmin; Zhang, Xiaolu; Zhang, Bo
2016-03-01
Linguistic units such as phonemes and syllables are important for speech perception. How the brain encodes these units is not well understood. Many neuroimaging studies have found distinct representations of consonant-vowel syllables that shared one phoneme and differed in the other phoneme (e.g. /ba/ and /da/), but it is unclear whether this discrimination ability is due to the neural coding of phonemes or syllables. We combined functional magnetic resonance imaging with multivariate pattern analysis to explore this question. Subjects listened to nine Mandarin syllables in a consonant-vowel form. We successfully decoded phonemes from the syllables based on the blood oxygenation level-dependent signals in the superior temporal gyrus (STG). Specifically, a classifier trained on the cortical patterns elicited by a set of syllables, which contained two phonemes, could distinguish the cortical patterns elicited by other syllables that contained the two phonemes. The results indicated that phonemes have unique representations in the STG. In addition, there was a categorical effect, i.e. the cortical patterns of consonants were similar, and so were the cortical patterns of vowels. Further analysis showed that phonemes exhibited stronger encoding specificity in the mid-STG than in the anterior STG. PMID:26751256
To demonstrate the functional neuroanatomy associated with sexual arousal visually evoked in depressed males who have underlying sexual dysfunction using Blood Oxygenation Level Dependent-based fMRI. Ten healthy volunteers (age range 21-55: mean 32.5 years), and 10 depressed subjects (age range 23-51: mean 34.4 years, mean Beck Depression Inventory score of 39.6 ± 5.9, mean Hamilton Rating Scale Depression (HAMD)-17 score of 33.5 ± 6.0) with sexual arousal dysfunction viewed erotic and neutral video films during functional magnetic resonance imaging (fMRI) with 1.5 T MR scanner (GE Signa Horizon). The fMRI data were obtained from 7 oblique planes using gradient-echo EPI (flip angle/TR/TE=90 .deg. /6000 ms/50 ms). The visual stimulation paradigm began with 60 sec of black screen, 150 sec of neutral stimulation with a documentary video film, 30 sec of black screen, 150 sec of sexual stimulation with an erotic video film followed by 30 sec of black screen. The brain activation maps and their quantification were analyzed by SPM99 program. There was a significant difference of brain activation between two groups during visual sexual stimulation. In depressed subjects, the level of activation during the visually evoked sexual arousal was significantly less than that of healthy volunteers, especially in the cerebrocortical areas of the hypothalamus, thalamus, caudate nucleus, and inferior and superior temporal gyri. On the other hand, the cerebral activation patterns during the neutral condition in both groups showed no significant differences (ρ < 0.01). This study is the first demonstration of the functional neuroanatomy of the brain associated with sexual dysfunction in depressed patients using fMRI. In order to validate our physiological neuroscience results, further studies that would include patients with other disorders and sexual dysfunction, and depressed patients without sexual dysfunction and their treatment response are needed
Yang, Jong Chul [Chonnam National Univ. Hospital, Kwangju (Korea, Republic of)
2004-06-15
To demonstrate the functional neuroanatomy associated with sexual arousal visually evoked in depressed males who have underlying sexual dysfunction using Blood Oxygenation Level Dependent-based fMRI. Ten healthy volunteers (age range 21-55: mean 32.5 years), and 10 depressed subjects (age range 23-51: mean 34.4 years, mean Beck Depression Inventory score of 39.6 {+-} 5.9, mean Hamilton Rating Scale Depression (HAMD)-17 score of 33.5 {+-} 6.0) with sexual arousal dysfunction viewed erotic and neutral video films during functional magnetic resonance imaging (fMRI) with 1.5 T MR scanner (GE Signa Horizon). The fMRI data were obtained from 7 oblique planes using gradient-echo EPI (flip angle/TR/TE=90 .deg. /6000 ms/50 ms). The visual stimulation paradigm began with 60 sec of black screen, 150 sec of neutral stimulation with a documentary video film, 30 sec of black screen, 150 sec of sexual stimulation with an erotic video film followed by 30 sec of black screen. The brain activation maps and their quantification were analyzed by SPM99 program. There was a significant difference of brain activation between two groups during visual sexual stimulation. In depressed subjects, the level of activation during the visually evoked sexual arousal was significantly less than that of healthy volunteers, especially in the cerebrocortical areas of the hypothalamus, thalamus, caudate nucleus, and inferior and superior temporal gyri. On the other hand, the cerebral activation patterns during the neutral condition in both groups showed no significant differences ({rho} < 0.01). This study is the first demonstration of the functional neuroanatomy of the brain associated with sexual dysfunction in depressed patients using fMRI. In order to validate our physiological neuroscience results, further studies that would include patients with other disorders and sexual dysfunction, and depressed patients without sexual dysfunction and their treatment response are needed.
Objective: To verify the accuracy of blood oxygenation level dependent (BOLD)-based activation using electrocortical stimulation mapping (ESM) and explore the value of language fMRI in the navigating operation of neurosurgery. Methods: In 8 cases with brain tumors, BOLD-fMRI examinations were done before the operations. Under the state of awake anesthesia,the patients were aroused and ESM was conducted. Point-to-point comparison between the BOLD signal activations and the ESM was carried out under the surveillance of the neuro-navigation technology. In order to observe the sensibility and specificity of BOLD activations, the location of BOLD activations and the point of ESM was compared to calculate the stimulating positive points inside the regions of BOLD signals (real positive), outside BOLD regions (pseudo- negative), the stimulating negative points inside the regions of BOLD signals (pseudo-positive), and outside BOLD region (real negative). Two kinds of criteria for assessment were used. One was that the positive stimulating points were located in BOLD regions, and the other was that the positive stimulating points were located within 1 cm around the range of BOLD regions. Removal of the lesions were conducted with the tissue 1 cm around the language region preserved, and the cortex inside 0.5-1.0 cm distance from the positive points were retained. Results: Of the 8 cases, only 6 finished the tasks. Among them, 3 cases were with astrocytoma of grade 2, 2 were with astrocytoma of grade 3, and one with glioblastoma. The total number of stimulating points was 48, among which the positive points were 11. When the first criteria was applied, the sensitivity was 72.7% (8/11), and the specificity was 81.8% (30/37). When the second criteria was applied, the sensitivity was 82.0% (9/11), and the specificity was 75.6% (28/37). Follow-up after operation showed no aphasia occurred. Conclusions: BOLD-fMRI had a high sensitivity and specificity in displaying the language
Niendorf, T; Pohlmann, A.; Arakelyan, K.; Flemming, B; Cantow, K.; Hentschel, J.; Grosenick, D; Ladwig, M.; Reimann, H; Klix, S.; Waiczies, S; Seeliger, E.
2015-01-01
Renal tissue hypoperfusion and hypoxia are key elements in the pathophysiology of acute kidney injury and its progression to chronic kidney disease. Yet, in vivo assessment of renal haemodynamics and tissue oxygenation remains a challenge. Many of the established approaches are invasive, hence not applicable in humans. Blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) offers an alternative. BOLD-MRI is non-invasive and indicative of renal tissue oxygenation. Nonetheles...
Kassim, A A; Umans, H; Nagel, R L; Fabry, M E
2000-09-01
Priapism is a common complication of sickle cell anemia. We report a little known sequela of priapism: painless megalophallus, with significant penile enlargement. The patient had had an intense episode of priapism 9 years previously and his penis remained enlarged. Blood oxygen level-dependent magnetic resonance imaging revealed enlarged, hypoxic corpora cavernosa. Megalophallus probably resulted from permanent loss of elasticity of the tunica albuginea due to severe engorgement during the episode of priapism. This sequela needs to be recognized by physicians because no intervention is necessary and sexual function seems to remain intact. PMID:10962334
Liu, Chong; Liu, Yong; Li, Weilan; Wang, Dawei; Jiang, Tianzi; Zhang, Yunting; Yu, Chunshui
2011-03-01
Although resting-state functional magnetic resonance imaging has shown altered functional connectivity between visual and other brain areas in the early blind individuals, it cannot answer which brain area's local activities are changed. In this study, regional homogeneity, a measure of the homogeneity of the local blood oxygen level-dependent signals, was used for the first time to investigate the changes in the resting-state brain activity in the early blind individuals. Compared with age-matched and sex-matched sighted individuals, the early blind individuals showed increased regional homogeneity only in the occipital areas, which might be explained by the abnormal cortical development and/or experience-dependent plasticity, resulted from an early visual deprivation. PMID:21304328
D'Souza Olympio
2010-02-01
Full Text Available Abstract Introduction Cerebral misery perfusion represents a failure of cerebral autoregulation. It is an important differential diagnosis in post-stroke patients presenting with collapses in the presence of haemodynamically significant cerebrovascular stenosis. This is particularly the case when cortical or internal watershed infarcts are present. When this condition occurs, further investigation should be done immediately. Case presentation A 50-year-old Caucasian man presented with a stroke secondary to complete occlusion of his left internal carotid artery. He went on to suffer recurrent seizures. Neuroimaging demonstrated numerous new watershed-territory cerebral infarcts. No source of arterial thromboembolism was demonstrable. Hypercapnic blood-oxygenation-level-dependent-contrast functional magnetic resonance imaging was used to measure his cerebrovascular reserve capacity. The findings were suggestive of cerebral misery perfusion. Conclusions Blood-oxygenation-level-dependent-contrast functional magnetic resonance imaging allows the inference of cerebral misery perfusion. This procedure is cheaper and more readily available than positron emission tomography imaging, which is the current gold standard diagnostic test. The most evaluated treatment for cerebral misery perfusion is extracranial-intracranial bypass. Although previous trials of this have been unfavourable, the results of new studies involving extracranial-intracranial bypass in high-risk patients identified during cerebral perfusion imaging are awaited. Cerebral misery perfusion is an important and under-recognized condition in which emerging imaging and treatment modalities present the possibility of practical and evidence-based management in the near future. Physicians should thus be aware of this disorder and of recent developments in diagnostic tests that allow its detection.
Ashley D Harris
Full Text Available Several recent studies have reported an inter-individual correlation between regional GABA concentration, as measured by MRS, and the amplitude of the functional blood oxygenation level dependent (BOLD response in the same region. In this study, we set out to investigate whether this coupling generalizes across cortex. In 18 healthy participants, we performed edited MRS measurements of GABA and BOLD-fMRI experiments using regionally related activation paradigms. Regions and tasks were the: occipital cortex with a visual grating stimulus; auditory cortex with a white noise stimulus; sensorimotor cortex with a finger-tapping task; frontal eye field with a saccade task; and dorsolateral prefrontal cortex with a working memory task. In contrast to the prior literature, no correlation between GABA concentration and BOLD activation was detected in any region. The origin of this discrepancy is not clear. Subtle differences in study design or insufficient power may cause differing results; these and other potential reasons for the discrepant results are discussed. This negative result, although it should be interpreted with caution, has a larger sample size than prior positive results, and suggests that the relationship between GABA and the BOLD response may be more complex than previously thought.
Purpose: to compare calf muscle Blood Oxygenation Level-Dependent (BOLD) response during ischemia in patients suffering from peripheral arterial occlusive disease (PAOD) and age-matched non-PAOD subjects. Materials and methods: PAOD patients with symptoms of intermittent calf claudication and an age-matched control group underwent T2*-weighted single-shot multi-echo planar imaging on a whole-body MR scanner at 1.5 T. The muscle BOLD signal in the calf was acquired during 60 sec of baseline and 240 sec of ischemia induced by cuff compression. T2* time courses in four calf muscles were evaluated. Results: significant differences in the mean T2* values were noted after 150 sec of measurement (p < 0.05). Patients with PAOD revealed a significantly reduced BOLD signal decrease compared to an age-matched control group. Conclusion: potential cause for this observation may be changes in the structure and/or the metabolic turnover of the muscle in PAOD patients. (orig.)
Potthast, Silke [Unispital Basel, Inst. fuer Radiologie (Switzerland); Schulte, A. [Univ. Hospital Ulm (Germany). Clinic for Radiation Therapy and Radiooncology; Kos, S.; Bilecen, D. [Unispital Basel, Interventional Radiology (Switzerland); Aschwanden, M. [Unispital Basel (Switzerland). Angiologie
2009-12-15
Purpose: to compare calf muscle Blood Oxygenation Level-Dependent (BOLD) response during ischemia in patients suffering from peripheral arterial occlusive disease (PAOD) and age-matched non-PAOD subjects. Materials and methods: PAOD patients with symptoms of intermittent calf claudication and an age-matched control group underwent T2*-weighted single-shot multi-echo planar imaging on a whole-body MR scanner at 1.5 T. The muscle BOLD signal in the calf was acquired during 60 sec of baseline and 240 sec of ischemia induced by cuff compression. T2* time courses in four calf muscles were evaluated. Results: significant differences in the mean T2* values were noted after 150 sec of measurement (p < 0.05). Patients with PAOD revealed a significantly reduced BOLD signal decrease compared to an age-matched control group. Conclusion: potential cause for this observation may be changes in the structure and/or the metabolic turnover of the muscle in PAOD patients. (orig.)
Seif, Maryam; Eisenberger, Ute; Binser, Tobias; Thoeny, Harriet C; Krauer, Fabienne; Rusch, Aurelia; Boesch, Chris; Vogt, Bruno; Vermathen, Peter
2016-06-01
Purpose To determine renal oxygenation changes associated with uninephrectomy and transplantation in both native donor kidneys and transplanted kidneys by using blood oxygenation level-dependent (BOLD) MR imaging. Materials and Methods The study protocol was approved by the local ethics committee. Thirteen healthy kidney donors and their corresponding recipients underwent kidney BOLD MR imaging with a 3-T imager. Written informed consent was obtained from each subject. BOLD MR imaging was performed in donors before uninephrectomy and in donors and recipients 8 days, 3 months, and 12 months after transplantation. R2* values, which are inversely related to tissue partial pressure of oxygen, were determined in the cortex and medulla. Longitudinal R2* changes were statistically analyzed by using repeated measures one-way analysis of variance with post hoc pair-wise comparisons. Results R2* values in the remaining kidneys significantly decreased early after uninephrectomy in both the medulla and cortex (P oxygen content. In donors, R2* remained significantly decreased in both the medulla and cortex at 3 (P < .01) and 12 (P < .01) months. In transplanted kidneys, R2* remained stable during the first year after transplantation, with no significant change. Among donors, cortical R2* was found to be negatively correlated with estimated glomerular filtration rate (R = -0.47, P < .001). Conclusion The results suggest that BOLD MR imaging may potentially be used to monitor renal functional changes in both remaining and corresponding transplanted kidneys. (©) RSNA, 2016. PMID:26744926
LI Shao-wu; WANG Jiang-fei; JIANG Tao; LI Shou-wei; ZHANG Wen-bo; LI Zi-xiao; ZHANG Zhong; DAI Jian-ping; WANG Zhong-cheng
2010-01-01
Background Localization of sensory cortical areas during the operation is essential to preserve the sensory function.Intraoperative direct electrostimulation under awake anesthesia is the golden standard but time-consuming. We applied 3T high field blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to identify the relationship between glioma and cortical sensory areas preoperatively and to guide intraoperative direct electrostimulation for quick and precise localization.Methods Five glioma patients with sensory cortex involvement by or next to the lesion had preoperative BOLD fMRI to determine the spatial relationship of cortical sensory areas to the tumours. Bilateral hand opposite movement was performed by these patients for fMRI. Precentral and postcentral gyri were identified by electrical stimulation during the operation. Karnofsky Performance Status scores of the patients' pre- and postoperative and the role of BOLD fMRI were evaluated.Results The cortical sensory areas were all activated in five glioma patients involving postcentral gyrus areas by BOLDf MRI with bilateral hand opposite movement. The detected activation areas corresponded with the results from cortical electrical stimulation.Conclusions The relationship between cortical sensory areas and tumour can be accurately shown by BOLD fMRI before operation. And the information used to make the tumour resection could obtain good clinical results.
XIE Jian; CHEN Xu-zhu; JIANG Tao; LI Shou-wei; LI Zi-xiao; ZHANG Zhong; DAI Jian-ping; WANG Zhong-cheng
2008-01-01
Background Blood oxygen level-dependent(BOLD)functional magnetic resonance imaging(fMRI)plays an important role in identifying functional cortical areas of the brain.especially In patients with gliomas.This study aimed to assess the value of fMRI in presurgical planning and functional outcome of patients with gliomas in the motor cortical areas.Methods Twenty-six patients with gliomas in the motor cortex were recruited in the study.Before operation.fMRI was performed in each patient to obtain the mapping of bilateral hands area on the primary sensorimotor cortex.This examination was performed on a 3.0T scanner with a bilateral hands movement paradigm.During microsurgery under awake anesthesia,the motor area was identified using direct electrical stimulation and compared with preoperative mapping.Finally the tumor was resected as much as possible with the motor cortex preserved in each patlent.Karnofsky performance status(KPS)was evaluated in all patients before and after operation.Results Twenty-three patients showed a successful fMRI mapping.Among them,19 were calssified to be grade Ⅲ;4,grade Ⅱ;3,grade Ⅰ.The operation time was about 7 hours in the 23 patients,8.5 hours in the other 3.The pre- and pOstODerative KPS score was 82.3±8.6 and 94.2±8.1,respectively.Conclusions Preoperative fMRI of the hand motor area shows a high consistency with intraoperative cortical electronic stimulation.Combined use of the two methods shows a maximum benefit in surgical treatment.
Julien Poublanc
2013-04-01
Full Text Available Introduction: Blood oxygen level-dependent (BOLD magnetic resonance imaging (MRI during manipulation of inhaled carbon dioxide (CO2 can be used to measure cerebrovascular reactivity (CVR and map regions of exhausted cerebrovascular reserve. These regions exhibit a reduced or negative BOLD response to inhaled CO2. In this study, we sought to clarify the mechanism behind the negative BOLD response by investigating its time delay (TD. Dynamic susceptibility contrast (DSC MRI with the injection of a contrast agent was used as the gold standard in order to provide measurement of the blood arrival time to which CVR TD could be compared. We hypothesize that if negative BOLD responses are the result of a steal phenomenon, they should be synchronized with positive BOLD responses from healthy brain tissue, even though the blood arrival time would be delayed. Methods: On a 3-tesla MRI system, BOLD CVR and DSC images were collected in a group of 19 patients with steno-occlusive cerebrovascular disease. For each patient, we generated a CVR magnitude map by regressing the BOLD signal with the end-tidal partial pressure of CO2 (PETCO2, and a CVR TD map by extracting the time of maximum cross-correlation between the BOLD signal and PETCO2. In addition, a blood arrival time map was generated by fitting the DSC signal with a gamma variate function. ROI masks corresponding to varying degrees of reactivity were constructed. Within these masks, the mean CVR magnitude, CVR TD and DSC blood arrival time were extracted and averaged over the 19 patients. CVR magnitude and CVR TD were then plotted against DSC blood arrival time. Results: The results show that CVR magnitude is highly correlated to DSC blood arrival time. As expected, the most compromised tissues with the longest blood arrival time have the lowest (most negative CVR magnitude. However, CVR TD shows a noncontinuous relationship with DSC blood arrival time. CVR TD is well correlated to DSC blood arrival time
Objective: To study the changes of motor cortex in patients with amyotrophic lateral sclerosis (ALS) while executing sequential finger tapping movement by using blood oxygenation level dependent (BOLD) functional MRI. Methods: Fifteen patients with definite or probable ALS and 15 age and gender matched normal controls were enrolled in the BOLD study, and all the subjects were right-handed with no other diseases or any recent medication history. A 3.0 T MR scanner' was employed and gradient echo EPI (GRE-EPI)sequence was used to acquire the functional images. Subjects executed sequential finger tapping movement at a frequency of 1-2 Hz during a block design task. fMRI data were analyzed by using statistical parametric mapping (SPM) 2. Volume of activated brain areas was compared with the use of a Student's t-test. Results: Bilateral primary sensorimotor cortex (PSM), bilateral posterior aspect of premotor area (PA), bilateral supplementary motor area (SMA), contralateral inferior lateral premotor area (ILPA), bilateral parietal region (PAR), and ipsilateral cerebellum showed activation in both ALS patients and normal controls when executing the same motor task. The activation areas in bilateral PSM and bilateral posterior aspect of PA ( right hand ipsilateral activation: ALS (924.5±141.1) mm3, control (829.9± 98.4) mm3, P=0.05; right hand contralateral activation: ALS (9143.8±702.8) mm3, control (8638.8±506.4) mm3 P3, control (902.5±3 184.2)mm, P3, control (5934.6±616.4) mm3, P3, control (4710.7±416.3) mm3, P3, control (3688.9±672.3) mm3, P3, control (254.3±84.4) mm3, P3, control (1689.0±719.6) mm3, P<0.05) were significantly larger in ALS patients than in normal controls. Extra activation areas including ipsilateral ILPA, contralateral cerebellum and bilateral posterior limb of internal capsule were only detected in ALS patients. Conclusions: Similar activation areas were seen in both groups while executing the same motor task, but the activated areas
Bo Liu; Zhiwei Li; Peng Xie
2014-01-01
Vertebral artery oriifce stenting may improve blood supply of the posterior circulation of the brain to regions such as the cerebellum and brainstem. However, previous studies have mainly focused on recovery of cerebral blood lfow and perfusion in the posterior circulation after inter-ventional therapy. This study examined the effects of functional recovery of local brain tissue on cerebellar function remodeling using blood oxygen level-dependent functional magnetic reso-nance imaging before and after interventional therapy. A total of 40 Chinese patients with severe unilateral vertebral artery oriifce stenosis were enrolled in this study. Patients were equally and randomly assigned to intervention and control groups. The control group received drug treat-ment only. The intervention group received vertebral artery oriifce angioplasty and stenting+identical drug treatment to the control group. At 13 days after treatment, the Dizziness Handicap Inventory score was compared between the intervention and control groups. Cerebellar function remodeling was observed between the two groups using blood oxygen level-dependent function-al magnetic resonance imaging. The improvement in dizziness handicap and cerebellar function was more obvious in the intervention group than in the control group. Interventional therapy for severe vertebral artery oriifce stenosis may effectively promote cerebellar function remodeling and exert neuroprotective effects.
Physiological and functional magnetic resonance imaging using balanced steady-state free precession
Park, Sung Hong; Han, Paul Kyu [Magnetic Resonance Imaging Lab, Dept. of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology, Daejeon(Korea, Republic of); Choi, Seung Hong [Dept. of Radiology, Seoul National University College of Medicine, Seoul (Korea, Republic of)
2015-06-15
Balanced steady-state free precession (bSSFP) is a highly efficient pulse sequence that is known to provide the highest signal-to-noise ratio per unit time. Recently, bSSFP is getting increasingly popular in both the research and clinical communities. This review will be focusing on the application of the bSSFP technique in the context of probing the physiological and functional information. In the first part of this review, the basic principles of bSSFP are briefly covered. Afterwards, recent developments related to the application of bSSFP, in terms of physiological and functional imaging, are introduced and reviewed. Despite its long development history, bSSFP is still a promising technique that has many potential benefits for obtaining high-resolution physiological and functional images.
Choi, Hye Young; Ko, Eun Sook; Han, Boo-Kyung; Kim, Eun Ju; Kim, Sun Mi; Lim, Yaeji; Kim, Rock Bum
2016-01-01
Objective To examine the relationship between magnetic resonance transverse relaxation rate (R2*) and prognostic factors. Materials and Methods A total of 159 women with invasive ductal carcinomas (IDCs) underwent breast magnetic resonance imaging (MRI) including blood oxygenation level-dependent (BOLD) sequence at 3 T. The distribution of the measured R2* values were analyzed, and the correlation between R2* and various prognostic factors (age, tumor size, histologic grade, lymphovascular invasion, and axillary lymph node status, as well as expression of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, p53, and Ki-67) were retrospectively assessed using patient medical records. Results The baseline R2* values of the IDCs were very heterogeneous with wide range among the patients. The mean R2* value was (32.8 ± 14.0) Hz with a median of 29.3 Hz (range 13.5–109.4 Hz). In multivariate analysis, older age was associated with decreased R2* value (P = 0.011) and IDCs with p53-overexpression showed higher R2* values than those without p53-overexpression group (P = 0.031). Other prognostic factors were not significantly correlated with R2* value. Conclusion In this study, R2* values were significantly correlated with age and expression of p53. Further studies are necessary to determine the prognostic value of BOLD-MRI. PMID:27384310
Kim, Chan Kyo; Park, Sung Yoon; Park, Byung Kwan [Sungkyunkwan University School of Medicine, Department of Radiology and Center for Imaging Science, Samsung Medical Center, Seoul (Korea, Republic of); Park, Won; Huh, Seung Jae [Sungkyunkwan University School of Medicine, Department of Radiation Oncology, Samsung Medical Center, Seoul (Korea, Republic of)
2014-07-15
To investigate the value of blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) as a predictor of therapeutic response in cervical cancer patients undergoing concurrent chemoradiotherapy (CCRT). Thirty consecutive patients with biopsy-proven cervical cancer were examined by BOLD MRI before (preTx) and after CCRT (postTx). The R2* value (s{sup -1}) was calculated in the tumour and normal myometrium for preTx and postTx studies. Final tumour responses, as determined by changes of tumour size or volume on MRI, were correlated with tumour R2* values at preTx. The mean R2* values of tumours at preTx (21.1) were significantly lower than those at postTx (39.4 s{sup -1}) (p < 0.001), while those of normal myometrium were similar between preTx and postTx (p = 0.363). At preTx, tumour R2* values showed significantly negative correlation with final tumour size response (p = 0.022, Spearman's coefficient = -0.415). However, tumour R2* values at preTx were not associated with final tumour volume response (p = 0.069). BOLD MRI at 3 T, as an imaging biomarker, may have the potential to evaluate therapeutic response in cervical cancers. The association between BOLD MRI findings and CCRT responses warrants further validation. (orig.)
Brown, Trecia A; Joanisse, Marc F; Gati, Joseph S; Hughes, Sarah M; Nixon, Pam L; Menon, Ravi S; Lomber, Stephen G
2013-01-01
Much of what is known about the cortical organization for audition in humans draws from studies of auditory cortex in the cat. However, these data build largely on electrophysiological recordings that are both highly invasive and provide less evidence concerning macroscopic patterns of brain activation. Optical imaging, using intrinsic signals or dyes, allows visualization of surface-based activity but is also quite invasive. Functional magnetic resonance imaging (fMRI) overcomes these limitations by providing a large-scale perspective of distributed activity across the brain in a non-invasive manner. The present study used fMRI to characterize stimulus-evoked activity in auditory cortex of an anesthetized (ketamine/isoflurane) cat, focusing specifically on the blood-oxygen-level-dependent (BOLD) signal time course. Functional images were acquired for adult cats in a 7 T MRI scanner. To determine the BOLD signal time course, we presented 1s broadband noise bursts between widely spaced scan acquisitions at randomized delays (1-12 s in 1s increments) prior to each scan. Baseline trials in which no stimulus was presented were also acquired. Our results indicate that the BOLD response peaks at about 3.5s in primary auditory cortex (AI) and at about 4.5 s in non-primary areas (AII, PAF) of cat auditory cortex. The observed peak latency is within the range reported for humans and non-human primates (3-4 s). The time course of hemodynamic activity in cat auditory cortex also occurs on a comparatively shorter scale than in cat visual cortex. The results of this study will provide a foundation for future auditory fMRI studies in the cat to incorporate these hemodynamic response properties into appropriate analyses of cat auditory cortex. PMID:23000258
Di, Ningning; Mao, Ning; Cheng, Wenna; Pang, Haopeng; Ren, Yan; Wang, Ning; Liu, Xinjiang; Wang, Bin
2016-01-01
Objective The aim of this study was to investigate whether the blood oxygenation level-dependent (BOLD) contrast magnetic resonance imaging (MRI) can evaluate tumor maturity and preoperatively differentiate prostate cancer (PCa) from benign prostate hyperplasia (BPH). Patients and methods BOLD MRI based on transverse relaxation time*-weighted echo planar imaging was performed to assess PCa (19) and BPH (22) responses to carbogen (95% O2 and 5% CO2). The average signal values of PCa and BPH before and after carbogen breathing and the relative increased signal values were computed, respectively. The endothelial-cell marker, CD31, and the pericyte marker, α-smooth muscle actin (mature vessels), were detected with immunofluorescence, and were assessed by microvessel density (MVD) and microvessel pericyte density (MPD). The microvessel pericyte coverage index (MPI) was used to evaluate the degree of vascular maturity. The changed signal from BOLD MRI was correlated with MVD, MPD, and MPI. Results After inhaling carbogen, both PCa and BPH showed an increased signal, but a lower slope was found in PCa than that in BPH (PMPI than BPH. The increased signal intensity was positively correlated with MPI in PCa and that in BPH (r=0.616, P=0.011; r=0.658, P=0.002); however, there was no correlation between the increased signal intensity and MPD or MVD in PCa than that in BPH (P>0.05). Conclusion Our results confirmed that the increased signal values induced by BOLD MRI well differentiated PCa from BPH and had a positive correlation with vessel maturity in both of them. BOLD MRI can be utilized as a surrogate marker for the noninvasive assessment of the degree of vessel maturity. PMID:27462169
Lin, Yu-Chun [Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Department of Electrical Engineering, Chang Gung University, Linkou, Taiwan (China); Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Wang, Jiun-Jie [Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Hong, Ji-Hong [Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Department of Radiation Oncology, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Lin, Yi-Ping [Department of Radiation Oncology, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Lee, Chung-Chi [Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Department of Radiation Oncology, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Wai, Yau-Yau; Ng, Shu-Hang; Wu, Yi-Ming [Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Linkou, Taiwan (China); Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Wang, Chun-Chieh, E-mail: jjwang@adm.cgmh.org.tw [Department of Medical Imaging and Radiological Sciences, Chang Gung University, Linkou, Taiwan (China); Department of Radiation Oncology, Chang Gung Memorial Hospital, Linkou, Taiwan (China)
2013-04-01
Purpose: The microvasculature of a tumor plays an important role in its response to radiation therapy. Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) and blood oxygen level-dependent (BOLD) MRI are both sensitive to vascular characteristics. The present study proposed a partial irradiation approach to a xenograft tumor to investigate the intratumoral response to radiation therapy using DCE and BOLD MRI. Methods and Materials: TRAMP-C1 tumors were grown in C57BL/6J mice. Partial irradiation was performed on the distal half of the tumor with a single dose of 15 Gy. DCE MRI was performed to derive the endothelium transfer constant, K{sup trans}, using pharmacokinetic analysis. BOLD MRI was performed using quantitative R2* measurements with carbogen breathing. The histology of the tumor was analyzed using hematoxylin and eosin staining and CD31 staining to detect endothelial cells. The differences between the irradiated and nonirradiated regions of the tumor were assessed using K{sup trans} values, ΔR2* values in response to carbogen and microvascular density (MVD) measurements. Results: A significantly increased K{sup trans} and reduced BOLD response to carbogen were found in the irradiated region of the tumor compared with the nonirradiated region (P<.05). Histologic analysis showed a significant aggregation of giant cells and a reduced MVD in the irradiated region of the tumor. The radiation-induced difference in the BOLD response was associated with differences in MVD and K{sup trans}. Conclusions: We demonstrated that DCE MRI and carbogen-challenge BOLD MRI can detect differential responses within a tumor that may potentially serve as noninvasive imaging biomarkers to detect microvascular changes in response to radiation therapy.
Wu, Pei-Hsin; Chung, Hsiao-Wen [Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Tsai, Ping-Huei [Imaging Research Center, Taipei Medical University, Taipei 11031, Taiwan and Department of Medical Imaging, Taipei Medical University Hospital, Taipei Medical University, Taipei 11031, Taiwan (China); Wu, Ming-Long, E-mail: minglong.wu@csie.ncku.edu.tw [Institute of Medical Informatics, National Cheng-Kung University, Tainan 70101, Taiwan and Department of Computer Science and Information Engineering, National Cheng-Kung University, Tainan 70101, Taiwan (China); Chuang, Tzu-Chao [Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan (China); Shih, Yi-Yu [Siemens Limited Healthcare Sector, Taipei 11503, Taiwan (China); Huang, Teng-Yi [Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China)
2013-12-15
Purpose: One of the technical advantages of functional magnetic resonance imaging (fMRI) is its precise localization of changes from neuronal activities. While current practice of fMRI acquisition at voxel size around 3 × 3 × 3 mm{sup 3} achieves satisfactory results in studies of basic brain functions, higher spatial resolution is required in order to resolve finer cortical structures. This study investigated spatial resolution effects on brain fMRI experiments using balanced steady-state free precession (bSSFP) imaging with 0.37 mm{sup 3} voxel volume at 3.0 T. Methods: In fMRI experiments, full and unilateral visual field 5 Hz flashing checkerboard stimulations were given to healthy subjects. The bSSFP imaging experiments were performed at three different frequency offsets to widen the coverage, with functional activations in the primary visual cortex analyzed using the general linear model. Variations of the spatial resolution were achieved by removing outerk-space data components. Results: Results show that a reduction in voxel volume from 3.44 × 3.44 × 2 mm{sup 3} to 0.43 × 0.43 × 2 mm{sup 3} has resulted in an increase of the functional activation signals from (7.7 ± 1.7)% to (20.9 ± 2.0)% at 3.0 T, despite of the threefold SNR decreases in the original images, leading to nearly invariant functional contrast-to-noise ratios (fCNR) even at high spatial resolution. Activation signals aligning nicely with gray matter sulci at high spatial resolution would, on the other hand, have possibly been mistaken as noise at low spatial resolution. Conclusions: It is concluded that the bSSFP sequence is a plausible technique for fMRI investigations at submillimeter voxel widths without compromising fCNR. The reduction of partial volume averaging with nonactivated brain tissues to retain fCNR is uniquely suitable for high spatial resolution applications such as the resolving of columnar organization in the brain.
MR-derived cerebral metabolic rate of oxygen utilization (CMRO2) has been suggested to be analogous to PET-derived CMRO2 and therefore may be used for detection of viable tissue at risk for infarction. The purpose of this study was to evaluate MR-derived CMRO2 mapping in acute ischemic stroke in relation to established diffusion- and perfusion-weighted imaging. In 23 patients (mean age 63 ± 18.7 years, 11 women) with imaging findings for acute ischemic stroke, relative oxygen extraction fraction was calculated from quantitative transverse relaxation times (T2, T2*) and relative cerebral blood volume using a quantitative blood oxygenation level dependent (BOLD) approach in order to detect a local increase of deoxyhemoglobin. Relative CMRO2 (rCMRO2) maps were calculated by multiplying relative oxygen extraction fraction (rOEF) by cerebral blood flow, derived from PWI. After co-registration, rCMRO2 maps were evaluated in comparison with apparent diffusion coefficient (ADC) and time-to-peak (TTP) maps. Mean rCMRO2 values in areas with diffusion-restriction or TTP/ADC mismatch were compared with rCMRO2 values in the contralateral tissue. In tissue with diffusion restriction, mean rCMRO2 values were significantly decreased compared to perfusion-impaired (17.9 [95 % confidence interval 10.3, 25.0] vs. 58.1 [95 % confidence interval 50.1, 70.3]; P < 0.001) and tissue in the contralateral hemisphere (68.2 [95 % confidence interval 61.4, 75.0]; P < 0.001). rCMRO2 in perfusion-impaired tissue showed no significant change compared to tissue in the contralateral hemisphere (58.1 [95 % confidence interval 50.1, 70.3] vs. 66.7 [95 % confidence interval 53.4, 73.4]; P = 0.34). MR-derived CMRO2 was decreased within diffusion-restricted tissue and stable within perfusion-impaired tissue, suggesting that this technique may be adequate to reveal different pathophysiological stages in acute stroke. (orig.)
Gersing, Alexandra S.; Schwaiger, Benedikt J. [Technical University Munich, Klinikum rechts der Isar, Department of Neuroradiology, Munich (Germany); University of California, Department of Radiology and Biomedical Imaging, San Francisco, CA (United States); Ankenbrank, Monika; Toth, Vivien; Bauer, Jan S.; Zimmer, Claus [Technical University Munich, Klinikum rechts der Isar, Department of Neuroradiology, Munich (Germany); Janssen, Insa [Technical University Munich, Department of Neurosurgery, Munich (Germany); Kooijman, Hendrik [Philips Healthcare, Hamburg (Germany); Wunderlich, Silke [Technical University Munich, Department of Neurology, Munich (Germany); Preibisch, Christine [Technical University Munich, Klinikum rechts der Isar, Department of Neuroradiology, Munich (Germany); Technical University Munich, Department of Neurology, Munich (Germany)
2015-12-15
MR-derived cerebral metabolic rate of oxygen utilization (CMRO{sub 2}) has been suggested to be analogous to PET-derived CMRO{sub 2} and therefore may be used for detection of viable tissue at risk for infarction. The purpose of this study was to evaluate MR-derived CMRO{sub 2} mapping in acute ischemic stroke in relation to established diffusion- and perfusion-weighted imaging. In 23 patients (mean age 63 ± 18.7 years, 11 women) with imaging findings for acute ischemic stroke, relative oxygen extraction fraction was calculated from quantitative transverse relaxation times (T2, T2*) and relative cerebral blood volume using a quantitative blood oxygenation level dependent (BOLD) approach in order to detect a local increase of deoxyhemoglobin. Relative CMRO{sub 2} (rCMRO{sub 2}) maps were calculated by multiplying relative oxygen extraction fraction (rOEF) by cerebral blood flow, derived from PWI. After co-registration, rCMRO{sub 2} maps were evaluated in comparison with apparent diffusion coefficient (ADC) and time-to-peak (TTP) maps. Mean rCMRO{sub 2} values in areas with diffusion-restriction or TTP/ADC mismatch were compared with rCMRO{sub 2} values in the contralateral tissue. In tissue with diffusion restriction, mean rCMRO{sub 2} values were significantly decreased compared to perfusion-impaired (17.9 [95 % confidence interval 10.3, 25.0] vs. 58.1 [95 % confidence interval 50.1, 70.3]; P < 0.001) and tissue in the contralateral hemisphere (68.2 [95 % confidence interval 61.4, 75.0]; P < 0.001). rCMRO{sub 2} in perfusion-impaired tissue showed no significant change compared to tissue in the contralateral hemisphere (58.1 [95 % confidence interval 50.1, 70.3] vs. 66.7 [95 % confidence interval 53.4, 73.4]; P = 0.34). MR-derived CMRO{sub 2} was decreased within diffusion-restricted tissue and stable within perfusion-impaired tissue, suggesting that this technique may be adequate to reveal different pathophysiological stages in acute stroke. (orig.)
Yuechun Li; Xiaoyan Liu; Guorong Liu; Ying He; Baojun Wang; Furu Liang; Li Wang; Hui Zhang; Jingfen Zhang; Ruiming Li
2006-01-01
BACKGROUND: Previous studies about blood oxygenation-level dependent (BOLD) functional MRI (fMRI) have indicated that the poststroke recovery of motor function is accompanied by the selective activation of motor cor texes with high correlation.OBJECTIVE: To evaluate the short-term outcomes after rehabilitative interventions with BOLD fMRI in hemi plegic patients with acute stroke, and analyze the correlation of the excitement of brain function in the passive and active movements of the affected limb with the recovery of motor function. DESIGN : A case observation. SETTING: Department of Neurology, Baotou Central Hospital. PARTICIPANTS: Thirty hemiplegic inpatients with ischemic stroke were selected from the Department of Neurology, Baotou Central Hospital from January to December in 2005, including 16 males and 14 females, aging 44-71 years with an average age of (56±5) years, and the disease course ranged from 12 to 72 hours. Inclusive criteria: In accordance with the diagnostic standard of ischemic stroke revised by the Fourth National Academic Meeting for Cerebrovascular Disease; Confirmed by cranial CT or MRI. They were all informed agreed with the detected items.METHODS: ① The Bobath technique was adopted in the rehabilitative interventions of the 30 patients, 30 minutes for each time, twice a day for three weeks continuously. ② The hand motor recovery of the stroke patients was graded by the Brunnstrom,stages ( Ⅰ -Ⅵ), and be able to grasp various objects and extend for the whole range was taken as grade Ⅵ. ③ The patients were examined with fMRI BOLD before rehabilitation and 3 weeks after rehabilitation. All the patients were trained with finger movements, the distracting thoughts should be eliminated as much as possible especially during the movement phase, the patients should highly concentrate on the hand movements. The range for the finger movements should be as large as possible with moderate frequency. The hand movements should be 10 s with
An Addendum to ``Detailed Balance has a Counterpart in Nonequilibrium Steady States''
Simha, Aditi; Evans, R. M. L.
2011-12-01
Transition rates in continuously driven steady states (relevant to sheared complex fluids) were derived in Evans (2004, 2005) by demanding that no information other than the microscopic laws of motion and the macroscopic observables of the system be used to describe it. This implies that the (nonequilibrium) reservoir, to which the system is weakly coupled, is fully characterized by its mean energy and mean flux. While we expect the resulting prescription for the rates in continuous- and discretized-time models to be equivalent, it is not trivial to see this from the expression for the rates derived in Evans (2005). We demonstrate this equivalence for a model of activated processes solved previously for continuous time (Evans 2005), thus demonstrating consistency of the theory.
Steady-state mass balance model for mercury in the St. Lawrence River near Cornwall, Ontario, Canada
We have developed a local mass balance model for the St. Lawrence River near Cornwall, Ontario that describes the fate and transport of mercury in three forms, elemental, divalent, and methylated, in a five compartment environment (air, water, sediments, periphyton, and benthos). Our objective was to construct a steady-state mass balance model to determine the dominant sources and sinks of mercury in this environment. We compiled mercury concentrations, fluxes, and transformation rates from previous studies completed in this section of the river to develop the model. The inflow of mercury was the major source to this system, accounting for 0.42 mol month−1, or 95.5% of all mercury inputs, whereas outflow was 0.28 mol month−1, or 63.6% of all losses, and sediment deposition was 0.12 mol month−1, or 27.3% of all losses. Uncertainty estimates were greatest for advective fluxes in surface water, porewater, periphyton, and benthic invertebrates. -- Highlights: ► Inflow accounted for 95.5% of all mercury inputs to the St. Lawrence River near Cornwall. ► Major losses of mercury were by outflow (63%) and sedimentation (27%). ► Sediments account for over 94% of all mercury in the system. -- A steady-state mass balance model is presented for mercury species in the St. Lawrence River near Cornwall, Ontario
Using bioprocess stoichiometry to build a plant-wide mass balance based steady-state WWTP model.
Ekama, G A
2009-05-01
Steady-state models are useful for design of wastewater treatment plants (WWTPs) because they allow reactor sizes and interconnecting flows to be simply determined from explicit equations in terms of unit operation performance criteria. Once the overall WWTP scheme is established and the main system defining parameters of the individual unit operations estimated, dynamic models can be applied to the connected unit operations to refine their design and evaluate their performance under dynamic flow and load conditions. To model anaerobic digestion (AD) within plant-wide WWTP models, not only COD and nitrogen (N) but also carbon (C) fluxes entering the AD need to be defined. Current plant-wide models, like benchmark simulation model No 2 (BSM2), impose a C flux at the AD influent. In this paper, the COD and N mass balance steady-state models of activated sludge (AS) organics degradation, nitrification and denitrification (ND) and anaerobic (AD) and aerobic (AerD) digestion of wastewater sludge are extended and linked with bioprocess transformation stoichiometry to form C, H, O, N, chemical oxygen demand (COD) and charge mass balance based models so that also C (and H and O) can be tracked through the whole WWTP. By assigning a stoichiometric composition (x, y, z and a in C(x)H(y)O(z)N(a)) to each of the five main influent wastewater organic fractions and ammonia, these, and the products generated from them via the biological processes, are tracked through the WWTP. The model is applied to two theoretical case study WWTPs treating the same raw wastewater (WW) to the same final sludge residual biodegradable COD. It is demonstrated that much useful information can be generated with the relatively simple steady-state models to aid WWTP layout design and track the different products exiting the WWTP via the solid, liquid and gas streams, such as aerobic versus anaerobic digestion of waste activated sludge, N loads in recycle streams, methane production for energy recovery
Helicity Balance and Steady-State Strength of the Dynamo Generated Galactic Magnetic Field
Kleeorin, N.; Moss, D.; Rogachevskii, I.; Sokoloff, D.
2002-01-01
We demonstrate that the inclusion of the helicity flux in the magnetic helicity balance in the nonlinear stage of galactic dynamo action results in a radical change in the magnetic field dynamics. The equilibrium value of the large-scale magnetic field is then approximately the equipartition level. This is in contrast to the situation without the flux of helicity, when the magnetic helicity is conserved locally, which leads to substantially subequipartition values for the equilibrium large-sc...
The goal of this study was to evaluate the ability of balanced steady state free precession (b-SSFP) magnetic resonance imaging sequence to distinguish between live and lysed iron-labelled cells. Human breast cancer cells were labelled with iron oxide nanoparticles. Cells were lysed using sonication. Imaging was performed at 3 T. The timing parameters for b-SSFP and the number of iron-labelled cells in samples were varied to optimise the b-SSFP signal difference between live and lysed iron-labelled cell samples. For in vivo experiments, cells were mixed with Matrigel and implanted into nude mice. Three mice implanted with live labelled cancer cells were irradiated to validate this method. Lysed iron-labelled cells have a significantly higher signal compared with live, intact iron-labelled cells in bSSFP images. The contrast between live and dead cells can be maximised by careful optimisation of timing parameters. A change in the b-SSFP signal was measured 6 days after irradiation, reflecting cell death in vivo. Histology confirmed the presence of dead cells in the implant. Our results show that the b-SSFP sequence can be optimised to allow for the discrimination of live iron-labelled cells and lysed iron-labelled cells in vitro and in vivo. (orig.)
Glockner, James F; Saranathan, Manojkumar; Bayram, Ersin; Lee, Christine U
2013-10-01
A novel 3D breath-held Dixon fat-water separated balanced steady state free precession (b-SSFP) sequence for MR cholangiopancreatography (MRCP) is described and its potential clinical utility assessed in a series of patients. The main motivation is to develop a robust breath-held alternative to the respiratory gated 3D Fast Spin Echo (FSE) sequence, the current clinical sequence of choice for MRCP. Respiratory gated acquisitions are susceptible to motion artifacts and blurring in patients with significant diaphragmatic drift, erratic respiratory rhythms or sleep apnea. A two point Dixon fat-water separation scheme was developed which eliminates signal loss arising from B0 inhomogeneity effects and minimizes artifacts from perturbation of the b-SSFP steady state. Preliminary results from qualitative analysis of 49 patients demonstrate robust performance of the 3D Dixon b-SSFP sequence with diagnostic image quality acquired in a 20-24s breath-hold. PMID:23876262
王文娟; 郭燕; 李竹浩; 蔡华崧; 史瑶平; 杨栋
2012-01-01
背景:血氧水平依赖的磁共振成像是目前惟一能无创性地监测肾血氧含量的方法.目的:探讨血氧水平依赖的磁共振成像在评价慢性肾病患者肾血氧水平、反映肾功能状态方面的价值.方法:对20名健康志愿者和24名慢性肾病患者行肾脏血氧水平依赖的磁共振成像,测量各组肾皮质及髓质的R2*值,并进行统计学分析.结果与结论:正常肾髓质的R2*值高于皮质(P 0.05).慢性肾病患者皮质及髓质的R2*值均高于正常人(P 0.05). Patients with chronic kidney disease had higher cortical and medullary R2*than normal health (P < 0.05). There was a positive correlation between serum creatinine and renal R2* (r=0.564, P =0.004;r=0.588, P =0.003). This research shows that blood oxygen level-dependent magnetic resonance imaging can reflect renal bloodoxygen levels, and has certain value in evaluate the renal function.
Objective: To evaluate blood oxygen level-dependent (BOLD) MRI on assessing renal damage after injection of iodine contrast medium with a 3.0 T system. Methods: Routine MRI examination, including T1WI and T2WI, and BOLD MRI were performed in 29 SD rats with a 3.0 T system before the injection of iodine contrast agent and 20 min, 24 h, 48 h, 72 h after the injection, respectively. T2 * and R2 * (=1/T2 *) measurements were obtained in the cortex, inner and outer medulla of kidney, respectively. The results obtained before contrast agent administration were considered as the self-controls. AVONA test were used for the comparison of R2 * values in different parts of both kidneys before contrast agent administration. Two-sample t test was used to compare R2 * values before and at each time point after contrast agent administration, and R2 * values in different parts of the kidneys. Results: Before contrast agent administration, R2 * values in outer medulla in both sides of kidney [R2 * leftOM =(31.76±2.73)/s , R2 * rightOM = (32.77±3.07)/s] were higher than those in cortex [R2 * leftC = (30.20±3.48)/s, R2 * rightC =(28.84±3.11)/s] and in inner medulla [R2 * leftIM =(29.54±2.42)/s, R2 * rightIM = (28.37±2.80)/s] (F=3.357 and 14.961, P2 * values in the three parts between left and right kidney, including cortex, outer and inner medulla (P>0.05). After contrast agent administration, R2 * values in outer medulla changed obviously, which reached to the peak values at 20 minutes after contrast agent administration [R2 * leftOM =(43.57±3.84)/s, R2 * rightOM =(44.58±3.13)/s] and dropped from 24 hours [R2 * leftOM =(42.07±4.82)/s, R2 * rightOM =(42.89±3.40)/s]. R2 * values in inner medulla and cortex only presented slight changes. Conclusion: R2 * values reflected the changes of oxygen content in renal cortex and medulla quantitatively, which helped for detecting medullar ischemia and hypoxia. BOLD MR imaging could offer a feasible method for evaluating oxygen
徐学勤; 陈楠; 李晓; 林晓珠; 朱晓雷; 倪根雄; 陈克敏; 严福华; 方文强; 徐耀文
2012-01-01
目的:探讨肾脏血氧水平依赖(blood oxygenation level-dependent,BOLD) MRI的临床应用价值.方法:对正常志愿者70例(无原发性和继发性肾病病史及肾功能损害危险因素)和57例慢性肾病患者进行GE 1.5THDMRI冠状面BOLD成像,分别测量其肾脏皮质及髓质的自旋弛豫率(R2*)值,并作对比分析.其中10例正常志愿者在1～6个月内进行了相同参数的冠状面BOLD成像检查.结果:T2*图像上,正常肾脏的结构清晰,皮质和髓质分界清,皮质和髓质R2*值分别为(12.63±1.40)/s和(18.14±2.51)/s,双侧肾脏皮质间(t=-1.333,P=0.186)、髓质间(t=0.958,P=0.341)的R2*值差异均无统计学意义.不同年龄及性别的志愿者间肾脏皮质、髓质R2*值亦均无统计学差异(P＞0.05).10例志愿者重复BOLD成像肾脏R2*值无统计学差异.T2*图像上,慢性肾病患者的皮髓质分界不清.正常志愿者与慢性肾病患者间肾髓质R2*值差异有统计学意义(P＜0.05).结论:肾脏BOLD MRI可清晰显示正常肾脏结构,有较好的可重复性,对慢性肾病患者肾髓质缺氧诊断较灵敏,具有较好的科研及临床应用前景.%Objective To evaluate the clinical application of blood oxygenation level-dependent (BOLD) MR imaging of kidney. Methods: Seventy healthy volunteers and 57 chronic kidney disease (CKD)patients underwent the BOLD MR imaging of the kidney with a 1.5-T MR imager (GE Signa Excite HD Twin-Speed 1.5T) . R2* of cortical and medullar portion of the kidney were calculated and compared. Reproducibility was assessed by repeating the same protocol in 10 randomly selected healthy volunteers after 1-6 months. R2* between patients and heallhy volunteers were compared. Results: In all healthy volunteers,there was a clear demarcation between cortex and medulla on T2* map. Medullary R2* were higher than cortical R2* (18.l4±2.51)/s,(12.63±1.40)/s. There was no difference in renal R2* between right and left kidney (Z.0.05),and no difference in
无
2007-01-01
BACKGROUND: Functional magnetic resonance imaging (fMRI) is initially used for visual cortex location.However, the application of fMRI in investigating the development of visual pathway lesions needs to be further observed.OBJECTIVE: This study is to longitudially observe the dynamic changes in cortical function and white matter fibrous structure of patients with visual pathway lesions by blood oxygenation level dependent-functional magnetic resonance imaging (BOLD-fMRI) combined with diffusion tensor imaging (DTI), and to analyze the characteristics of brain function and structural recombination at convalescent period of lesions.DESIGN: Randomized controlled observation.SETTING: Department of Radiology, the General Hospital of Nanjing Military Area Command of Chinese PLA.PARTICIPANTS: Eight patients with unilateral or bilateral visual disorder caused by visual pathway lesions,who admitted to Department of Radiology, the General Hospital of Nanjing Military Area Command of Chinese PLA from January to September 2006 were involved, and served as experimental subjects. The patients, 6 males and 2 females, were aged 16 - 67 years. They had visual disorder confirmed by clinical examination, i.e. visual pathway lesion, which was further diagnosed by MR or CT. Another 12 subjects generally matching to those patients of experimental group in gender, age and sight, who received health examination in synchronization were involved and served as controls. The subjects had no history of eye diseases. Their binocular visual acuity (or corrected visual acuity) was over 1.0. Both routine examination of ophthalmology and examination of fundus were normal. Informed consents of detected items were obtained from all the subjects.METHODS: Signa Excite HD 1.5T magnetic resonance imaging system with 16 passages (GE Company,USA) and coil with 8 passages were used; brain functional stimulus apparatus (SAV-8800. Meide Company) was used for showing experimental mission. At the early stage
Ø. Kaste
2002-01-01
Full Text Available The steady-state First-order Acidity Balance (FAB model for calculating critical loads of sulphur (S and nitrogen (N is applied to 609 Norwegian soft-water lakes to assess the future nitrate (NO3‾ leaching potential under present (1992-96 S and N deposition. The lakes were separated into five groups receiving increasing levels of N deposition (-2yr-1. Using long-term sustainable N sink rates presently recommended for FAB model applications, N immobilisation, net N uptake in forests, denitrification and in-lake N retention were estimated for each group of lakes. Altogether, the long-term N sinks constituted 9.9 ± 3.2 to 40.5 ± 11.4 meq m-2yr-1 in the lowest and highest N deposition categories, respectively. At most sites, the current N deposition exceeds the amount of N retained by long-term sustainable N sinks plus the NO3‾ loss via the lake outlets. This excess N, which is currently retained within the catchments may, according to the FAB model, leach as acidifying NO3‾ in the future. If these predictions are fulfilled, NO3‾ leaching at sites in the various N deposition categories will increase dramatically from present (1995 mean levels of 1-20 meq m-2yr-1, to mean levels of 7-70 meq m-2yr-1 at future steady state. To illustrate the significance of such an increase in NO3‾ leaching, the mean Acid Neutralising Capacity (ANC at sites in the highest N deposition category may decrease from -18 ± 15 μeq L-1 at present, to -40 ± 20 μeq L-1. Under present S and N deposition levels, the FAB model predicts that 46% of the Norwegian lakes may experience exceedances of critical loads for acidifying deposition. In comparison, the Steady-State Water Chemistry model (SSWC, which considers only the present N leaching level, estimates critical load exceedances in 37% of the lakes under the same deposition level. Thus far, there are great uncertainties regarding both the time scales and the extent of future N leaching, and it is largely unknown
Chen, Hai-Wei; Zhang, Qiu-Ju; Fan, Sheng-Yao
2011-04-01
A new approach is used in this paper to analyze steady-state response of a vertical axis automatic washing machine with a hydraulic balancer and a method for getting a smaller deflection angle of the washing/drying assembly is presented. First, a mathematical model of the vertical axis washing machine and a numerical description of the hydraulic balancer are described and a vibration model for the vertical axis washing machine with a hydraulic balancer is built. Second, the vibration model is transformed into an autonomous form whose equilibrium point can be used to analyze dynamics of the washing machine at the steady state. Because the autonomous form can be solved by the Newton-Raphson method which requires only a few iterations, it provides a much faster approach for analyzing steady-state response of the spin drying process than traditional numerical integration methods. Five parameters influencing the spin drying process are considered, and the balancer's importance in reducing vibrations at the steady state is illustrated. Third, the equilibrium conditions of the centrifugal forces acting on the clothes, the washing/drying assembly and the balancer are considered, and a governing equation for getting a smaller deflection angle of the washing/drying assembly is derived. At last, parameters in the governing equation, especially those related to the hydraulic balancer, are discussed.
Objective: To investigate balanced steady-state free precession with flow-sensitive dephasing magnetization preparation (FSD-bSSFP) in the assessment of arteries of foot in diabetic patients. Methods: The lower-extremity peripheral arteries of 43 diabetic patients were evaluated by FSD-bSSFP no contrast MRA and contrast-enhanced MRA (CE-MRA) in. Two experienced observers assessed the image quality, degree of venous contaminated and visibility of pedal artery branches by FSD-bSSFP and CE-MRA respectively in consensus. The signal intensity (SI), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the source images of both groups were measured and Wilcoxon and t tests were performed. Results: The image score of FSD-bSSFP group was 2.7±1.1 and CE-MRA was 2.6±0.8, there was no statistical difference (Z= 0.134, P>0.05). The image score of demonstration of the pedal artery branches and degree of venous contamination on FSD-bSSFP were 3.2±0.9 and 1.8±0.4 respectively which were superior to that of CE-MRA (2.5±0.9 and 2.1±0.8 respectively). Significant statistical difference existed between the two groups in demonstration of pedal artery branches (Z=5.246, P0.05). But CNR of CE-MRA was superior to that of FSD-bSSFP and significant statistical difference existed between these two methods (t=5.113, P<0.01). Conclusion: FSD-bSSFP without contrast could be used in the evaluation of foot arteries in patients of renal dysfunction and diabetes. (authors)
Okell, Thomas W; Schmitt, Peter; Bi, Xiaoming; Chappell, Michael A; Tijssen, Rob H N; Sheerin, Fintan; Miller, Karla L; Jezzard, Peter
2016-06-01
Vessel-selective dynamic angiograms provide a wealth of useful information about the anatomical and functional status of arteries, including information about collateral flow and blood supply to lesions. Conventional x-ray techniques are invasive and carry some risks to the patient, so non-invasive alternatives are desirable. Previously, non-contrast dynamic MRI angiograms based on arterial spin labeling (ASL) have been demonstrated using both spoiled gradient echo (SPGR) and balanced steady-state free precession (bSSFP) readout modules, but no direct comparison has been made, and bSSFP optimization over a long readout period has not been fully explored. In this study bSSFP and SPGR are theoretically and experimentally compared for dynamic ASL angiography. Unlike SPGR, bSSFP was found to have a very low ASL signal attenuation rate, even when a relatively large flip angle and short repetition time were used, leading to a threefold improvement in the measured signal-to-noise ratio (SNR) efficiency compared with SPGR. For vessel-selective applications, SNR efficiency can be further improved over single-artery labeling methods by using a vessel-encoded pseudo-continuous ASL (VEPCASL) approach. The combination of a VEPCASL preparation with a time-resolved bSSFP readout allowed the generation of four-dimensional (4D; time-resolved three-dimensional, 3D) vessel-selective cerebral angiograms in healthy volunteers with 59 ms temporal resolution. Good quality 4D angiograms were obtained in all subjects, providing comparable structural information to 3D time-of-flight images, as well as dynamic information and vessel selectivity, which was shown to be high. A rapid 1.5 min dynamic two-dimensional version of the sequence yielded similar image features and would be suitable for a busy clinical protocol. Preliminary experiments with bSSFP that included the extracranial vessels showed signal loss in regions of poor magnetic field homogeneity. However, for intracranial vessel
Multiple Steady States in Distillation
Bekiaris, Nikolaos
1995-01-01
We study multiple steady states in distillation. We first analyze the simplest case of ternary homogeneous azeotropic mixtures. We show that in the case of infinite reflux and an infinite number of trays (∞/∞ case) one can construct bifurcation diagrams on physical grounds with the distillate flow as the bifurcation parameter. Multiple steady states exist when the distillate flow varies non-monotonically along the continuation path of the bifurcation diagram. We derive a necessary and suffici...
Variational methods in steady state diffusion problems
Classical variational techniques are used to obtain accurate solutions to the multigroup multiregion one dimensional steady state neutron diffusion equation. Analytic solutions are constructed for benchmark verification. Functionals with cubic trial functions and conservational lagrangian constraints are exhibited and compared with nonconservational functionals with respect to neutron balance and to relative flux and current at interfaces. Excellent agreement of the conservational functionals using cubic trial functions is obtained in comparison with analytic solutions
Steady-State Process Modelling
Cameron, Ian; Gani, Rafiqul
illustrate the “equation oriented” approach as well as the “sequential modular” approach to solving complex flowsheets for steady state applications. The applications include the Williams-Otto plant, the hydrodealkylation (HDA) of toluene, conversion of ethylene to ethanol and a bio-ethanol process.......This chapter covers the basic principles of steady state modelling and simulation using a number of case studies. Two principal approaches are illustrated that develop the unit operation models from first principles as well as through application of standard flowsheet simulators. The approaches...
Owens, J. A.
1982-01-01
Options for faculty utilization in a steady state are examined, with consideration for their economy or ability to increase turnover or flexibility: early retirement, part retirement, retraining, exchange with other institutions or industry, and fixed-term appointments or lecturer positions. (MSE)
Steady-State Process Modelling
Cameron, Ian; Gani, Rafiqul
2011-01-01
illustrate the “equation oriented” approach as well as the “sequential modular” approach to solving complex flowsheets for steady state applications. The applications include the Williams-Otto plant, the hydrodealkylation (HDA) of toluene, conversion of ethylene to ethanol and a bio-ethanol process....
Steady-state eternal inflation
Since the advent of inflation, several theorems have been proven suggesting that although inflation can (and generically does) continue eternally into the future, it cannot be extended eternally into the past to create a 'steady-state' model with no initial time. Here we provide a construction that circumvents these theorems and allows a self-consistent, geodesically complete, and physically sensible steady-state eternally inflating universe, based on the flat slicing of de Sitter space. This construction could be used as the background spacetime for creation events that form big-bang-like regions, and hence could form the basis for a cosmology that is compatible with observations and yet which avoids an initial singularity or beginning of time
Steady state neutral beam injector
Learning from operational reliability of neutral beam injectors in particular and various heating schemes including RF in general on TFTR, JET, JT-60, it has become clear that neutral beam injectors may find a greater role assigned to them for maintaining the plasma in steady state devices under construction. Many technological solutions, integrated in the present day generation of injectors have given rise to capability of producing multimegawatt power at many tens of kV. They have already operated for integrated time >105 S without deterioration in the performance. However, a new generation of injectors for steady state devices have to address to some basic issues. They stem from material erosion under particle bombardment, heat transfer > 10 MW/m2, frequent regeneration of cryopanels, inertial power supplies, data acquisition and control of large volume of data. Some of these engineering issues have been addressed to in the proposed neutral beam injector for SST-1 at our institute; the remaining shall have to wait for the inputs of the database generated from the actual experience with steady state injectors. (author)
Siple Dome: Is it in Steady State?
Pettit, E. C.; Waddington, E. D.; Nereson, N. A.; Zumberge, M. A.; Hamilton, G. S.
2001-12-01
Changes in the West Antarctic Ice Sheet since the end of the last ice age have implications for how we interpret its present behavior, in terms of both its stability and its record of climate history. Siple Dome, the ridge between Ice Streams C and D, is not presently thinning and is close to being in balance with present environmental conditions. We present three independent measurements of ice thickness change in the divide region of Siple Dome: a GPS surface horizontal strain network, fiber optic vertical strain measurements at depth, and precision GPS measurements of vertical motion of near-surface ice ("coffee-can" method). From the horizontal strain network, we calculate the divergence of the horizontal velocity. This divergence is equal to the gradient of vertical velocity at the surface and, with some assumptions about the distribution of strain rates with depth, we can calculate the vertical velocity at the surface. For steady state, the vertical velocity must be balanced by the local accumulation rate. The fiber optic instruments provide a profile of the relative vertical velocity with depth. We fit a theoretical vertical velocity pattern to these data and extrapolate to find the surface vertical velocity. Our third method (coffee-can) directly measures the vertical motion of a marker 20 meters deep using precision GPS and compares it with the local long-term rate of snow accumulation to calculate the net rate of ice sheet thickness change. All three methods reach the same conclusion: Siple Dome is currently very close to being in steady state. This result has two implications. First, ice dynamics models developed to interpret radar images or ice core data can assume steady state behavior, simplifying the models. Second, our result suggests that the central part of the Ross Embayment may have had a low-elevation profile during the late Holocene, even though other areas of the WAIS may have been thicker.
Ao, P
2008-01-01
From a logic point of view this is the third in the series to solve the problem of absence of detailed balance. This paper will be denoted as SDS III. The existence of a dynamical potential with both local and global meanings in general nonequilibrium processes has been controversial. Following an earlier explicit construction by one of us (Ao, J. Phys. {\\bf A37}, L25 '04, arXiv:0803.4356, referred to as SDS II), in the present paper we show rigorously its existence for a generic class of situations in physical and biological sciences. The local dynamical meaning of this potential function is demonstrated via a special stochastic differential equation and its global steady-state meaning via a novel and explicit form of Fokker-Planck equation, the zero mass limit. We also give a procedure to obtain the special stochastic differential equation for any given Fokker-Planck equation. No detailed balance condition is required in our demonstration. For the first time we obtain here a formula to describe the noise in...
李成; 房向东; 罗丹丹; 龚良庚; 连珞; 曾磊; 周国盛; 樊烨; 徐高四; 涂卫平
2014-01-01
Objective To investigate the application of diffusion - weighted imaging(DWI)and blood oxygen level -dependent MRI(BOLD MRI)in the evaluation of renal function of chronic kidney disease(CKD), Methods A total of 50 pa-tients with CKD who went to Department of Nephrology,the Second Affiliated Hospital of Nanchang University from February to December in 2012,were included in CKD group,20 healthy volunteers were included in control group, The ADC and R2 * values of bilateral cortex and medulla were measured by DWI and BOLD MRI among two groups, According to GFR measured by 99 Tcm -DTPA scintigraphy,CKD group were divided into 3 groups:CKD1 stage group(16 cases);CKD2 stage group(13 cases);CKD3 stage group(21 cases), The changes of ADC and R2 * values among patients with different CKD stages were analyzed, A total of 18 patients received renal biopsy,the correlation between pathological lesion degree and ADC and R2 * values of cortex and medulla was analysed, Results The ADC and R2 * values of bilateral cortex and medulla in CKD1 group,CKD2 group and CKD3 group were significantly lower than those in control group(P 0, 05), The medullary R2 * values were correlated negatively with pathological lesion degree(r = - 0, 659,P 0,05）；髓质 R2*值与病理损害积分呈负相关（r =-0,659，P <0,05）。结论肾实质 ADC 值可无创性反映 CKD 肾功能水平及肾脏病理状态的改变。R2*值可以评价 CKD 肾脏髓质的氧代谢的改变，且对于判断 CKD 肾脏病理损伤的程度有一定意义。
Inconsistencies in steady state thermodynamics
Dickman, Ronald; Motai, Ricardo
2014-03-01
We address the issue of extending thermodynamics to nonequilibrium steady states. Using driven stochastic lattice gases, we ask whether consistent definitions of an effective chemical potential μ, and an effective temperature Te, are possible. These quantities are determined via zero-flux conditions of particles and energy between the driven system and a reservoir. For the models considered here, the fluxes are given in terms of certain stationary average densities, eliminating the need to perturb the system by actually exchanging particles; μ and Te are thereby obtained via open-circuit measurements, using a virtual reservoir. In the lattice gas with nearest-neighbor exclusion, temperature is not relevant, and we find that the effective chemical potential, a function of density and drive strength, satisfies the zeroth law, and correctly predicts the densities of coexisting systems. In the Katz-Lebowitz-Spohn driven lattice gas, both μ and Te need to be defined. We show analytically that the zeroth law is violated, and determine the size of the violations numerically. Our results highlight a fundamental inconsistency in the extension of thermodynamics to nonequilibrium steady states. Research supported by CNPq, Brazil.
Chemical reaction systems with toric steady states
Millan, Mercedes Perez; Shiu, Anne; Conradi, Carsten
2011-01-01
Mass-action chemical reaction systems are frequently used in Computational Biology. The corresponding polynomial dynamical systems are often large, consisting of tens or even hundreds of ordinary differential equations, and poorly parameterized (due to noisy measurement data and a small number of data points and repetitions). Therefore, it is often difficult to establish the existence of (positive) steady states or to determine whether more complicated phenomena such as multistationarity exist. If, however, the steady state ideal of the system is a binomial ideal, then we show that these questions can be answered easily. The focus of this work is on systems with this property, and we say that such systems have toric steady states. Our main result gives sufficient conditions for a chemical reaction system to have toric steady states. Furthermore, we analyze the capacity of such a system to exhibit positive steady states and multistationarity. Examples of systems with toric steady states include weakly-reversib...
石会兰; 郑振峰; 马慧; 李峰坦; 张敬; 张云亭
2014-01-01
目的：探讨正常肾脏的血氧水平依赖磁共振（BOLD-MRI）成像特点，以及与部分生理指标之间的相关性。方法纳入90例行腹部磁共振检查的非肾脏病患者。使用GE 3.0 T磁共振扫描仪和Torsopa相控阵线圈，行肾脏冠状面T1WI及BOLD成像，BOLD-MRI成像扫描采用T2*自旋梯度回波（T2*SPGR）序列，BOLD影像分析采用R2*map后处理软件，分别从肾脏皮质和髓质区选取感兴趣区（ROI）测量表观自旋-自旋弛豫率(R2*)值。分析R2*值与患者年龄、性别、身高、体质量、体质量指数（BMI）、体表面积（BSA）和估算的肾小球滤过率（eGFR）之间的相关性。结果两侧肾脏皮质区R2*值[左侧（16.56±1.40）Hz和右侧（16.66±1.28）Hz]均低于相应髓质区[左侧（28.82±3.71）Hz和右侧（28.36±3.72）Hz]；女性和男性患者皮质R2*值[女性（16.55±1.30）Hz和男性（16.66±1.38Hz）]也低于相应的髓质区[女性（28.46±3.64）Hz和男性（28.70±3.78）Hz]。双侧肾脏髓质区肾脏下极R2*值[（27.29±3.05）]Hz低于中极[（29.32±3.47）Hz]和上极[（29.16±4.21）Hz]；差异均有统计学意义。髓质R2*值与年龄呈正相关，与eGFR呈负相关(r分别为0.284、-0.232,均P<0.05)。结论 R2*值可反映肾脏皮髓质氧分压的水平，判断其缺血缺氧程度。BOLD-MRI提供了一种简单、易行且无创性检测肾脏皮髓质氧代谢的方法。%Objective To explore the characteristics of blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) in healthy native kidneys. To investigate the relationship between BOLD-MRI and common physiological in-dexes. Methods GE 3.0T MRI scanner and Torsopa phased-array coil were employed to acquire renal coronal T1WI and BOLD image. Ninety patients who were ruled out chronic kidney diseases underwent BOLD-MRI with T2*-spoiled gradient recalled echo (T2*SPGR) sequence. BOLD images were analyzed on R2*map software. Cortical and
Multiplicity of monetary steady states
Ryoji Hiraguchi; Keiichiro Kobayashi
2014-01-01
In the Lagos-Wright model of money, monetary frictions alone cannot be a source of equilibrium multiplicity. However, the conclusion depends on the assumption that the agents always enter the centralized market after completing a transaction in the decentralized markets. In this paper, we investigate a monetary model in which the centralized market opens once, but the decentralized markets open twice in each period. We show that as the sellers money balances affect the buyers problem in the f...
A Steady State Tokamak Operation by Use of Magnetic Monopoles
Narihara, K.
1991-01-01
A steady state tokamak operation based on a magnetic monopole circuit is considered. Circulation of a chain of iron cubes which trap magnetic monopoles generates the needed loop voltage. The monopole circuit is enclosed by a series of solenoid coils in which the magnetic field is feedback controlled so that the force on the circuit balance against the mechanical friction. The driving power is supplied through the current sources of poloidal, ohmic and solenoid coils. The current drive efficie...
2010-07-01
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Persistent Probability Currents in Non-equilibrium Steady States
Zia, Royce; Mellor, Andrew; Mobilia, Mauro; Fox-Kemper, Baylor; Weiss, Jeffrey
For many interesting phenomena in nature, from all life forms to the global climate, the fundamental hypothesis of equilibrium statistical mechanics does not apply. Instead, they are perhaps better characterized by non-equilibrium steady states, evolving with dynamical rules which violate detailed balance. In particular, such dynamics leads to the existence of non-trivial, persistent probability currents - a principal characteristic of non-equilibrium steady states. In turn, they give rise to the notion of 'probability angular momentum'. Observable manifestations of such abstract concepts will be illustrated in two distinct contexts: a heterogeneous nonlinear voter model and our ocean heat content. Supported in part by grants from the Bloom Agency (Leeds, UK) and the US National Science Foundation: OCE-1245944. AM acknowledges the support of EPSRC Industrial CASE Studentship, Grant No. EP/L50550X/1.
A steady state theory for processive cellulases
Cruys-Bagger, Nicolaj; Olsen, Jens Elmerdahl; Præstgaard, Eigil;
2013-01-01
remains to be fully developed. In this paper, we suggest a deterministic kinetic model that relies on a processive set of enzyme reactions and a quasi steady-state assumption. It is shown that this approach is practicable in the sense that it leads to mathematically simple expressions for the steady-state...... rate, and only requires data from standard assay techniques as experimental input. Specifically, it is shown that the processive reaction rate at steady state may be expressed by a hyperbolic function related to the conventional Michaelis–Menten equation. The main difference is a ‘kinetic processivity....... This has significant kinetic implications, for example the maximal specific rate (Vmax/E0) for processive cellulases is much lower than the catalytic rate constant (kcat). We discuss how relationships based on this theory may be used in both comparative and mechanistic analyses of cellulases....
Multiple steady state phenomenon in martensitic transformation
无
2001-01-01
Based on the basic facts that the martensitic transformation is a physical phenomenon which occurs in non-equilibrium conditions and there exists the feedback mechanism in the martensitic transformation, the dynamical processes of the isothermal and athermal martensitic transformations were analyzed by using nonlinear theory and a bifurcation theory model was established. It is shown that a multiple steady state phenomenon can take place as austenite is cooled, and the transitions of the steady state temperature between the branches of stable steady states can be considered the transformation from austenite to martensite. This model can estimate the starting temperature of the martensitic transformation and explain some experimental features of the martensitic transformation such as the effects of cooling rate, fluctuation and austenitic grain size on the martensitic transformation.
Steady-state spheromak reactor studies
After summarizing the essential elements of a gun-sustained spheromak, the potential for a steady-state is explored by means of a comprehensive physics/engineering/costing model. A range of cost-optimized reactor design points is presented, and the sensitivity of cost to key physics, engineering, and operational variables is reported
Thermodynamics of Stability of Nonequilibrium Steady States.
Rastogi, R. P.; Shabd, Ram
1983-01-01
Presented is a concise and critical account of developments in nonequilibrium thermodynamics. The criterion for stability of nonequilibrium steady states is critically examined for consecutive and monomolecular triangular reactions, autocatalytic reactions, auto-inhibited reactions, and the Lotka-Volterra model. (JN)
Mimicking Nonequilibrium Steady States with Time-Periodic Driving
Raz, O.; Subaşı, Y.; Jarzynski, C.
2016-04-01
Under static conditions, a system satisfying detailed balance generically relaxes to an equilibrium state in which there are no currents. To generate persistent currents, either detailed balance must be broken or the system must be driven in a time-dependent manner. A stationary system that violates detailed balance evolves to a nonequilibrium steady state (NESS) characterized by fixed currents. Conversely, a system that satisfies instantaneous detailed balance but is driven by the time-periodic variation of external parameters—also known as a stochastic pump (SP)—reaches a periodic state with nonvanishing currents. In both cases, these currents are maintained at the cost of entropy production. Are these two paradigmatic scenarios effectively equivalent? For discrete-state systems, we establish a mapping between nonequilibrium stationary states and stochastic pumps. Given a NESS characterized by a particular set of stationary probabilities, currents, and entropy production rates, we show how to construct a SP with exactly the same (time-averaged) values. The mapping works in the opposite direction as well. These results establish a proof of principle: They show that stochastic pumps are able to mimic the behavior of nonequilibrium steady states, and vice versa, within the theoretical framework of discrete-state stochastic thermodynamics. Nonequilibrium steady states and stochastic pumps are often used to model, respectively, biomolecular motors driven by chemical reactions and artificial molecular machines steered by the variation of external, macroscopic parameters. Our results loosely suggest that anything a biomolecular machine can do, an artificial molecular machine can do equally well. We illustrate this principle by showing that kinetic proofreading, a NESS mechanism that explains the low error rates in biochemical reactions, can be effectively mimicked by a constrained periodic driving.
Optimization of steady-state beam-driven tokamak reactors
Recent developments in neutral beam technology prompt us to reconsider the prospects for steady-state tokamak reactors. A mathematical reactor model is developed that includes the physics of beam-driven currents and reactor power balance, as well as reactor and beam system costs. This model is used to find the plasma temperatures that minimize the reactor cost per unit of net electrical output. The optimum plasma temperatures are nearly independent of β and are roughly twice as high as the optimum temperatures for ignited reactors. If beams of neutral deuterium atoms with near-optimum energies of 1 to 2 MeV are used to drive the current in a reactor the size of the International Tokamak Reactor, then the optimum temperatures are typically T /SUB e/ approx. = 12 to 15 keV and T /SUB i/ approx. = 17 to 21 keV for a wide range of model parameters. Net electrical output rises rapidly with increasing deuterium beam energy for E /SUB b/ less than or equal to 400 keV, but rises only slowly above E /SUB b/ about 1 MeV. We estimate that beam-driven steady-state reactors could be economically competitive with pulsed-ignition reactors if cyclic-loading problems limit the toroidal magnetic field strength of pulsed reactors to less than or equal to 85% of that allowed in steady-state reactors
Optimization of steady-state beam-driven tokamak reactors
Recent developments in neutral beam technology prompt us to reconsider the prospects for steady-state tokamak reactors. A mathematical reactor model is developed which includes the physics of beam-driven currents and reactor power balance, as well as reactor and beam system costs. This model is used to find the plasma temperatures which minimize the reactor cost per unit of net electrical output. The optimum plasma temperatures are nearly independent of β and are roughly twice as high as the optimum temperatures for ignited reactors. If beams of neutral deuterium atoms with near-optimum energies of 1 to 2 MeV are used to drive the current in an INTOR-sized reactor, then the optimum temperatures are typically T/sub e/ approx. = 12 to 15 keV and T/sub i/ approx. = keV for a wide range of model parameters. Net electrical output rises rapidly with increasing deuterium beam energy for E/sub b/ less than or equal to 400 keV, but rises only slowly above E/sub b/ approx. 1 MeV. We estimate that beam-driven steady-state reactors could be economically competitive with pulsed-ignition reactors if cyclic-loading problems limit the toroidal magnetic field strength of pulsed reactors to less than or equal to 85% of that allowed in steady-state reactors
Control algorithms for quasi-steady-state reactor operation
Specialized algorithms for digitally controlling the quasi-steady-state operation of reactors can be derived from the well-known neutron and energy balance equations for reactors. Utilizing the appropriate assumptions, these equations can be reduced to yield the classical proportional-integral-derivative feedback control approach. This method may be applied to single- or multiple-region reactors to control fuel temperature or neutron flux by manipulating system reactivity, specifically control rod reactivity. This paper discusses the development of single- and multiple-region flux and temperature control as well as numerical and experimental testing of these algorithms
Steady State Analysis of Towed Marine Cables
WANG Fei; HUANG Guo-liang; DENG De-heng
2008-01-01
Efficient numerical schemes were presented for the steady state solutions of towed marine cables. For most of towed systems, the steady state problem can be resolved into two-point boundary-value problem, or initial value problem in some special cases where the initial values are available directly. A new technique was proposed and attempted to solve the two-point boundary-value problem rather than the conventional shooting method due to its algorithm complexity and low efficiency. First, the boundary conditions are transformed into a set of nonlinear governing equations about the initial values, then bisection method is employed to solve these nonlinear equations with the aid of 4th order Runge-Kutta method. In common sense, non-uniform (sheared) current is assumed, which varies in magnitude and direction with depth. The schemes are validated through the DE Zoysa's example, then several numerical examples are also presented to illustrate the numerical schemes.
Development of steady state magnetic sensor
Hara, Shigemitsu; Nakayama, Takahide [Hitachi Ltd., Tokyo (Japan); Nagashima, Akira; Kasai, Satoshi
1998-12-01
A prototype of new mechanical sensor based on the steady state electromagnetic force (J x B force) measurement has been developed and tested. The mechanical force sensor is a new type of the magnetic sensor which is available for frequencies smaller than 0.1 Hz. The prototype of the mechanical sensor has been examined, and the following results were obtained; (1) A signal was proportional to simulated force in the load cell tests. (2) A signal drift concerning the temperature was reproducible over the range of the ITER environment. (3) A signal was proportional to the magnetic field in the steady state magnetic field measurement tests. (4) A load cell linearity error did not increase significantly after irradiation of 7.2 x 10{sup 6} Gy. These results indicate that the mechanical sensor will provide the practical feasibility in the long time magnetic field measurement. (author)
Steady State versus Pulsed Tokamak DEMO
Full text: The present report deals with a Review of problems for a Steady state(SS) DEMO, related argument is treated about the models and the present status of comparison between the characteristics of DEMO pulsed versus a Steady state device.The studied SS DEMO Models (SLIM CS, PPCS model C EU-DEMO, ARIES-RS) are analyzed from the point of view of the similarity scaling laws and critical issues for a steady state DEMO. A comparison between steady state and pulsed DEMO is therefore carried out: in this context a new set of parameters for a pulsed (6 — 8 hours pulse) DEMO is determined working below the density limit, peak temperature of 20 keV, and requiring a modest improvement in the confinement factor(HIPBy2 = 1.1) with respect to the H-mode. Both parameters density and confinement parameter are lower than the DEMO models presently considered. The concept of partially non-inductive pulsed DEMO is introduced since a pulsed DEMO needs heating and current drive tools for plasma stability and burn control. The change of the main parameter design for a DEMO working at high plasma peak temperatures Te ∼ 35 keV is analyzed: in this range the reactivity increases linearly with temperature, and a device with smaller major radius (R = 7.5 m) is compatible with high temperature. Increasing temperature is beneficial for current drive efficiency and heat load on divertor, being the synchrotron radiation one of the relevant components of the plasma emission at high temperatures and current drive efficiency increases with temperature. Technology and engineering problems are examined including efficiency and availability R&D issues for a high temperature DEMO. Fatigue and creep-fatigue effects of pulsed operations on pulsed DEMO components are considered in outline to define the R&D needed for DEMO development. (author)
Terminal Value Techniques in Equity Valuation - Implications of the Steady State Assumption
Levin, Joakim; Olsson, Per M.
2000-01-01
This paper examines the conditions necessary for calculating steady state terminal values in equity (company) valuation models. We make explicit use of the fact that a company's income statements and balance sheets can be modeled as a system of difference equations. From these difference equations, we derive conditions for steady state. The conditions ensure that the company remains qualitatively similar year by year after the valuation horizon and that it has a stable development of earnings...
On Typicality in Nonequilibrium Steady States
Evans, Denis J.; Williams, Stephen R.; Searles, Debra J.; Rondoni, Lamberto
2016-08-01
From the statistical mechanical viewpoint, relaxation of macroscopic systems and response theory rest on a notion of typicality, according to which the behavior of single macroscopic objects is given by appropriate ensembles: ensemble averages of observable quantities represent the measurements performed on single objects, because " almost all" objects share the same fate. In the case of non-dissipative dynamics and relaxation toward equilibrium states, " almost all" is referred to invariant probability distributions that are absolutely continuous with respect to the Lebesgue measure. In other words, the collection of initial micro-states (single systems) that do not follow the ensemble is supposed to constitute a set of vanishing, phase space volume. This approach is problematic in the case of dissipative dynamics and relaxation to nonequilibrium steady states, because the relevant invariant distributions attribute probability 1 to sets of zero volume, while evolution commonly begins in equilibrium states, i.e., in sets of full phase space volume. We consider the relaxation of classical, thermostatted particle systems to nonequilibrium steady states. We show that the dynamical condition known as Ω T-mixing is necessary and sufficient for relaxation of ensemble averages to steady state values. Moreover, we find that the condition known as weak T-mixing applied to smooth observables is sufficient for ensemble relaxation to be independent of the initial ensemble. Lastly, we show that weak T-mixing provides a notion of typicality for dissipative dynamics that is based on the (non-invariant) Lebesgue measure, and that we call physical ergodicity.
Potential multiple steady-states in the long-term carbon cycle
Tennenbaum, Stephen; Schwartzman, David
2013-01-01
Modelers of the long term carbon cycle in Earth history have previously assumed there is only one stable climatic steady state. Here we investigate the possibility of multiple steady states. We find them in Abiotic World, lacking any biotic influence, resulting from possible variations in planetary albedo in different temperature, atmospheric carbon dioxide level regimes, with the same weathering forcing balancing a volcanic source to the atmosphere, ocean pool. In Plant World modeling relevant to the Phanerozoic, we include the additional effects of biotic enhancement of weathering on land, organic carbon burial, oxidation of reduced organic carbon in terrestrial sediments and the variation of biotic productivity with temperature, finding a second stable steady state appearing between twenty and fifty degrees C. The very warm early Triassic climate may be the prime candidate for an upper temperature steady state. Given our results, the anthropogenic driven rise of atmospheric carbon dioxide could potentially...
Accelerator based steady state neutron source
Using high current, cw linear accelerator technology, a spallation neutron source can achieve much higher average intensities than existing or proposed pulsed spallation sources. With about 100 mA of 300 MeV protons or deuterons, the accelerator based neutron research facility (ABNR) would initially achieve the 1016 n/cm2s thermal flux goal of the advanced steady state neutron source, and upgrading could provide higher steady state fluxes. The relatively low ion energy compared to other spallation sources has an important impact on R and D requirements as well as capital cost, for which a range of $300-450 M is estimated by comparison to other accelerator-based neutron source facilities. The source is similar to a reactor source is most respects. It has some higher energy neutrons but fewer gamma rays, and the moderator region is free of many of the design constraints of a reactor, which helps to implement sources for various neutron energy spectra, many beam tubes, etc., with the development of a multibeam concept and the basis for currents greater than 100 mA that is assumed in the R and D plan, the ABNR would serve many additional uses, such as fusion materials development, production of proton-rich isotopes, and other energy and defense program needs
An accelerator based steady state neutron source
Using high current, cw linear accelerator technology, a spallation neutron source can achieve much higher average intensities than existing or proposed pulsed spallation sources. With about 100 mA of 300 MeV protons or deuterons, the accelerator based neutron research facility (ABNR) would initially achieve the 1016 n/cm2 s themal flux goal of the advanced steady state neutron source, and upgrading could provide higher steady state fluxes. The relatively low ion energy compared to other spallation sources has an important impact on R and D requirements as well as capital cost, for which a range of Dollar 300-450 is estimated by comparison to other accelerator-based neutron source facilities. The source is similar to a reactor source in most respects. It has some higher energy neutrons but fewer gamma rays, and the moderator region is free of many of the design constraints of a reactor, which helps to implement sources for various neutron energy spectra, many beam tubes, etc. With the development of a multibeam concept and the basis for currents greater than 100 mA that is assumed in the R and D plan, the ABNR would serve many additional uses, such as fusion materials development, production of proton-rich isotopes, and other energy and defense program needs. (orig.)
Steady state phreatic surfaces in sloping aquifers
Loáiciga, Hugo A.
2005-08-01
Steady state groundwater flow driven by constant recharge in an unconfined aquifer overlying sloping bedrock is shown to be represented, using the Dupuit approximation, by an ordinary differential equation of the Abel type y(x) . y'(x) + a . y(x) + x = 0, whose analytical solution is derived in this work. This article first investigates the case of zero saturated thickness at the upstream boundary, a flow system reminiscent of perched groundwater created by percolation of precipitation or irrigation in a sloping aquifer fully draining at its downstream boundary. A variant of this flow system occurs when the phreatic surface mounds and produces groundwater discharge toward the upstream boundary. This variant is a generalization of the classical groundwater flow problem involving two lakes connected by an aquifer, the latter being on sloping terrain in this instance. Analytical solutions for the phreatic surface's steady state geometry are derived for the case of monotonically declining hydraulic head as well as for the case of a mounded phreatic surface. These solutions are of practical interest in drainage studies, slope stability, and runoff formation investigations. It is shown that the flow factor a = -$\\sqrt{{\\rm K}/{\\rm N} tan β (where K, N, and tan β are the hydraulic conductivity, vertical recharge, and aquifer slope, respectively) has a commanding role on the phreatic surface's solutions. Two computational examples illustrate the implementation of this article's results.
Steady state flow evaluations for passive auxiliary feedwater system of APR
This paper briefly introduces a methodology to evaluate steady state flow of APR+ Passive Auxiliary Feedwater System (PAFS). The PAFS is being developed as a safety grade passive system to completely replace the existing active Auxiliary Feedwater System (AFWS). Natural circulation cooling can be generally classified into the single-phase, two-phase, and boiling-condensation modes. The PAF is designed to be operated in a boiling-condensation natural circulation mode. The steady-state flow rate should be equal to the steady-state boiling/condensation rate determined by the steady-state energy and momentum balances in the PAFS. The determined steady-state flow rate can be used in the design optimization for the natural circulation loop of the PAFS through the steady-state momentum balance. Since the retarding force, which is to be balanced by the driving force in the natural circulation system design depends on the reliable evaluation of the success of a natural circulation system design depends on the reliable evaluation of the pressure loss coefficients. In PAFS, the core decay heat is released by natural circulation flow between the S G secondary side and the Passive Condensation Heat Exchanger (PCHX) that is immersed in the Passive Condensation Cooling Tank (PCCT). The PCCT is located on the top of Auxiliary building The driving force is determined by the difference between the S/G (heat Source) secondary water level and condensation liquid (heat sink) level. It will overcome retarding force at flowrate in the system, which is determined by vaporization and condensation of the steam which is generated at the S/G by the latent heat in system. In this study, the theoretical method to estimate the steady state flow rate in boiling-condensation natural circulation system is developed and compared with test results
Magnetic sensor for steady state tokamak
Neyatani, Yuzuru; Mori, Katsuharu; Oguri, Shigeru; Kikuchi, Mitsuru [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment
1996-06-01
A new type of magnetic sensor has been developed for the measurement of steady state magnetic fields without DC-drift such as integration circuit. The electromagnetic force induced to the current which leads to the sensor was used for the measurement. For the high frequency component which exceeds higher than the vibration frequency of sensor, pick-up coil was used through the high pass filter. From the results using tokamak discharges, this sensor can measure the magnetic field in the tokamak discharge. During {approx}2 hours measurement, no DC drift was observed. The sensor can respond {approx}10ms of fast change of magnetic field during disruptions. We confirm the extension of measured range to control the current which leads to the sensor. (author).
Advances of blood oxygen-level dependent MRI in muscular system
BOLD-fMRI has been applied to muscular system to observe muscular pathophysiological change after performing a task and show the characteristics of muscle perfusion. This paper mainly introduces the scanning sequence, common tasking methods, such as cuff compression, excise, oxygen and drug, etc. It also introduces clinical study of perfusion reserve of muscular tissue with abnormal blood vessels. (authors)
Open Markov processes: A compositional perspective on non-equilibrium steady states in biology
Pollard, Blake S
2016-01-01
In recent work, Baez, Fong and the author introduced a framework for describing Markov processes equipped with a detailed balanced equilibrium as open systems of a certain type. These `open Markov processes' serve as the building blocks for more complicated processes. In this paper, we describe the potential application of this framework in the modeling of biological systems as open systems maintained away from equilibrium. We show that non-equilibrium steady states emerge in open systems of this type, even when the rates of the underlying process are such that a detailed balanced equilibrium is permitted. It is shown that these non-equilibrium steady states minimize a quadratic form which we call `dissipation.' In some circumstances, the dissipation is approximately equal to the rate of change of relative entropy plus a correction term. On the other hand, Prigogine's principle of minimum entropy production generally fails for non-equilibrium steady states. We use a simple model of membrane transport to illus...
Mimicking Nonequilibrium Steady States with Time-Periodic Driving
Raz, Oren; Subasi, Yigit; Jarzynski, Christopher
Under static conditions, a system satisfying detailed balance generically relaxes to an equilibrium state in which there are no currents: to generate persistent currents, either detailed balance must be broken or the system must be driven in a time-dependent manner. A stationary system that violates detailed balance evolves to a nonequilibrium steady state (NESS) characterized by fixed currents. Conversely, a system that satisfies instantaneous detailed balance but is driven by the time-periodic variation of external parameters - also known as a stochastic pump (SP) - reaches a periodic state with non-vanishing currents. In both cases, these currents are maintained at the cost of entropy production. Are these two paradigmatic scenarios effectively equivalent? For discrete-state systems we establish a mapping between NESS and SP. Given a NESS characterized by a particular set of stationary probabilities, currents and entropy production rates, we show how to construct a SP with exactly the same (time-averaged) values. The mapping works in the opposite direction as well. These results establish a proof of principle: they show that SP are able to mimic the behavior of NESS, and vice-versa, within the theoretical framework of discrete-state stochastic thermodynamics.
Chikui, Toru; Tokumori, Kenji; Kazunori, Yoshiura (Dept. of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu Univ., Fukuoka (Japan)), e-mail: chikui@rad.dent.kyushu-u.ac.jp; Shiraishi, Tomoko; Yuasa, Kenji (Section of Image Diagnosis, Dept. of Diagnostics and General Care, Fukuoka Dental College, Fukuoka (Japan)); Inatomi, Daisuke (Dept. of Radiology, Fukuoka Dental College Medical and Dental Hospital, Fukuoka (Japan)); Hatakenaka, Masamitsu (Dept. of Clinical Radiology, Faculty of Medical Science, Kyushu Univ., Fukuoka (Japan))
2010-07-15
Background: The persistent muscle contractions during clenching are thought to cause some temporomandibular disorders. However, no report has so far evaluated the effect of clenching on the masticatory muscles by magnetic resonance imaging (MRI). Purpose: To investigate the effect of clenching with maximum voluntary contraction on the T1, T2, and signal intensity (SI) of the balanced fast field-echo (b FFE) of the masseter muscle. Material and Methods: A total of 11 volunteers participated. Multi-echo spin-echo echo-planar imaging was used for T2 measurements, and multi-shot Look-Locker sequence for T1 measurements. The Look-Locker sequence has been used for fast T1 mapping and this method has been applied for the imaging of various tissues. In addition, the b FFE was used due to the high temporal resolution. These three sequences lasted for 10 min and the participants were instructed to clench from 60 s to 80 s after the start of the data acquisition. T2, T1, and SI were normalized compared to pre-clenching values. Results: T2 decreased by clenching, which reflected a decrease of tissue perfusion due to the mechanical pressure. It increased rapidly after the clenching (peak value, 1.11+-0.03; peak time, 16.8+-7.6 s after the clenching), which corresponded to the reactive hyperemia and later, it gradually returned to the initial values (half period, 2.22+-0.84 min). The change in the SI of the b FFE was triphasic and similar to that of T2 clenching. T1 increased after the cessation of the clenching and later gradually decreased during the recovery periods. However, the change of T1 was quite different from that of T2, with a lower peak value (1.04+-0.02), a later peak time (36.0+-28.0 s), and a longer half period (4.76+-3.40 min) (P<0.0001, 0.0066, 0.02, respectively). Conclusion: The change in T2 was triphasic and we considered that it predominantly reflected the tissue perfusion.
Steady State Vapor Bubble in Pool Boiling
Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C.; Maroo, Shalabh C.
2016-02-01
Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.
Steady State Vapor Bubble in Pool Boiling.
Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C; Maroo, Shalabh C
2016-01-01
Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics. PMID:26837464
Steady-state creep in the mantle
G. RANALLI
1977-06-01
Full Text Available SUMMARY - The creep equations for steady-state flow of olivine at high
pressure and temperature are compared in an attempt to elucidate the rheological
behaviour of the mantle. Results are presented in terms of applied deformation
maps and curves of effective viscosity v depth.
In the upper mantle, the transition stress between dislocation and diffusion
creep is between 10 to 102 bar (as orders of magnitude for grain sizes from
0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
viscosity, than under oceans. Predominance of one creep mechanism above the
others depends on grain size, strain rate, and volume fraction of melt; the
rheological response can be different for different geodynamic processes.
In the lower mantle, on the other hand, dislocation creep is predominant
at all realistic grain sizes and strain rates. If the effective viscosity has to be only
slightly higher than in the upper mantle, as some interpretations of glacioisostatic
rebound suggest, then the activation volume cannot be larger than
11 cm3 mole^1.
Constrained optimal steady-state control for isolated traffic intersections
Jack HADDAD; David MAHALEL; Ilya IOSLOVICH; Per-Olof GUTMAN
2014-01-01
The steady-state or cyclic control problem for a simplified isolated traffic intersection is considered. The optimization problem for the green-red switching sequence is formulated with the help of a discrete-event max-plus model. Two steady-state control problems are formulated: optimal steady-state with green duration constraints, and optimal steady-state control with lost time. In the case when the criterion is a strictly increasing, linear function of the queue lengths, the steady-state control problems can be solved analytically. The structure of constrained optimal steady-state traffic control is revealed, and the effect of the lost time on the optimal solution is illustrated.
A mathematical model of pan evaporation under steady state conditions
Lim, Wee Ho; Roderick, Michael L.; Farquhar, Graham D.
2016-09-01
In the context of changing climate, global pan evaporation records have shown a spatially-averaged trend of ∼ -2 to ∼ -3 mm a-2 over the past 30-50 years. This global phenomenon has motivated the development of the "PenPan" model (Rotstayn et al., 2006). However, the original PenPan model has yet to receive an independent experimental evaluation. Hence, we constructed an instrumented US Class A pan at Canberra Airport (Australia) and monitored it over a three-year period (2007-2010) to uncover the physics of pan evaporation under non-steady state conditions. The experimental investigations of pan evaporation enabled theoretical formulation and parameterisation of the aerodynamic function considering the wind, properties of air and (with or without) the bird guard effect. The energy balance investigation allowed for detailed formulation of the short- and long-wave radiation associated with the albedos and the emissivities of the pan water surface and the pan wall. Here, we synthesise and generalise those earlier works to develop a new model called the "PenPan-V2" model for application under steady state conditions (i.e., uses a monthly time step). Two versions (PenPan-V2C and PenPan-V2S) are tested using pan evaporation data available across the Australian continent. Both versions outperformed the original PenPan model with better representation of both the evaporation rate and the underlying physics of a US Class A pan. The results show the improved solar geometry related calculations (e.g., albedo, area) for the pan system led to a clear improvement in representing the seasonal cycle of pan evaporation. For general applications, the PenPan-V2S is simpler and suited for applications including an evaluation of long-term trends in pan evaporation.
Kajian Peluang Steady State Pada Rantai Markov
Novalina, Mariantan
2011-01-01
Markov chain says that the conditional probability of any future event given any past even and the present state is independent of the past event and depend only upon the present state. = is the transition probability from state i to state j The transition probability of well-balanced situation level is the transition probability which has reached balance so that will not change to change of time that happened or change that phase that happened. Formally, the transition probabi...
Defining Features of Steady-State Timbres
Hall, Michael D.
1995-01-01
Three experiments were conducted to define steady -state features of timbre for a group of well-trained musicians. Experiment 1 evaluated whether or not pairs of three critical dimensions of timbre--spectral slope (6 or 12 dB/octave), formant structure (/a/ or /i/ vowel), and inharmonicity of partials (harmonic or inharmonic)--were processed in a separable or integral fashion. Accuracy and speed for classification of values along one dimension were examined under different conditions of variability along a second dimension (fixed, correlated, or orthogonal). Spectral slope and formant structure were integral, with classification speed for the target dimension depending upon variability along the orthogonal dimension. In contrast, evidence of asymmetric separability was obtained for inharmonicity. Classification speed for slope and formant structure did not depend on inharmonicity, whereas RT for the target dimension of inharmonicity was strongly influenced by variability along either slope or formant structure. Since the results of Experiment 1 provided a basis for manipulating spectral slope and formant structure as a single feature, these dimensions were correlated in Experiment 2. Subjects searched for targets containing potential features of timbre within arrays of 1-4 inharmonic distractor pitches. Distractors were homogeneous with respect to the dimensions of timbre. When targets had /a/ formants with shallow spectral slopes, search time increased nonlinearly with array size in a manner consistent with the parallel processing of items, and thus feature search. Feature search was not obtained for targets with /i/ formants and steep slopes. Thus, the feature was coded as the presence or absence of /a/ formants with shallow spectral slopes. A search task using heterogeneous distractor values along slope/formant structure was used in Experiment 3 to evaluate whether or not the feature of timbre and pitch were automatically conjoined (integral). Search times for
Positive Steady States of a Competitor-Competitor-Mutualist Model
Wen-yan Chen; Ming-xin Wang
2004-01-01
In this paper we deal with the positive steady states of a Competitor-Competitor-Mutualist model with diffusion and homogeneous Dirichlet boundary conditions.We rst give the necessary conditions,and then establish the su cient conditions for the existence of positive steady states.
The aim of this study was to compare the three-dimensional fat-suppressed balanced non-steady-state free precession (3D FS-nSSFP) sequence and the 3D T1-weighted spoiled gradient-recalled echo (3D T1-GRE) sequence for evaluating lumbar nerve root compression with continuous thin-slice coronal magnetic resonance (MR) images. The institutional review board approved this study, and written informed consent was obtained from all 35 patients. We optimized continuous 2.5-mm thick lumbar coronal images with 3D FS-nSSFP and 3D T1-GRE. We calculated the contrast-to-noise ratio (CNR) for nerve roots and other structures on images with the two sequences. With knowledge of the final diagnosis, we assessed the visibility of nerve root compression on these images. The CNR values of nerve roots were significantly higher on images with 3D FS-nSSFP than on those with 3D T1-GRE. These continuous thin-slice coronal images facilitated visualization of nerve root compression in >91% of patients. There was no statistically significant difference between the two sequences in the detection of nerve root compression. Continuous thin-slice coronal MR images using 3D FS-nSSFP and 3D T1-GRE sequences are sufficient to evaluate lumbar nerve root compression, and 3D FS-nSSFP is superior to 3D T1-GRE for depiction of lumbar nerve roots. (author)
Steady State of Pedestrian Flow in Bottleneck Experiments
Liao, Weichen; Seyfried, Armin; Chraibi, Mohcine; Drzycimski, Kevin; Zheng, Xiaoping; Zhao, Ying
2015-01-01
Experiments with pedestrians could depend strongly on initial conditions. Comparisons of the results of such experiments require to distinguish carefully between transient state and steady state. In this work, a feasible algorithm - Cumulative Sum Control Chart - is proposed and improved to automatically detect steady states from density and speed time series of bottleneck experiments. The threshold of the detection parameter in the algorithm is calibrated using an autoregressive model. Comparing the detected steady states with previous manually selected ones, the modified algorithm gives more reproducible results. For the applications, three groups of bottleneck experiments are analysed and the steady states are detected. The study about pedestrian flow shows that the difference between the flows in all states and in steady state mainly depends on the ratio of pedestrian number to bottleneck width. When the ratio is higher than a critical value (approximately 115 persons/m), the flow in all states is almost ...
Steady-State Performance of Kalman Filter for DPLL
QIAN Yi; CUI Xiaowei; LU Mingquan; FENG Zhenming
2009-01-01
For certain system models, the structure of the Kalman filter is equivalent to a second-order vari-able gain digital phase-locked loop (DPLL). To apply the knowledge of DPLLs to the design of Kalman filters, this paper studies the steady-state performance of Kalman filters for these system models. The results show that the steady-state Kalman gain has the same form as the DPLL gain. An approximate simple form for the steady-state Kalman gain is used to derive an expression for the equivalent loop bandwidth of the Kalman filter as a function of the process and observation noise variances. These results can be used to analyze the steady-state performance of a Kalman filter with DPLL theory or to design a Kalman filter model with the same steady-state performance as a given DPLL.
An implicit steady-state initialization package for the RELAP5 computer code
A direct steady-state initialization (DSSI) method has been developed and implemented in the RELAP5 hydrodynamic analysis program. It provides a means for users to specify a small set of initial conditions which are then propagated through the remainder of the system. The DSSI scheme utilizes the steady-state form of the RELAP5 balance equations for nonequilibrium two-phase flow. It also employs the RELAP5 component models and constitutive model packages for wall-to-phase and interphase momentum and heat exchange. A fully implicit solution of the linearized hydrodynamic equations is implemented. An implicit coupling scheme is used to augment the standard steady-state heat conduction solution for steam generator use. It solves the primary-side tube region energy equations, heat conduction equations, wall heat flux boundary conditions, and overall energy balance equation as a coupled system of equations and improves convergence. The DSSI method for initializing RELAP5 problems to steady-state conditions has been compared with the transient solution scheme using a suite of test problems including; adiabatic single-phase liquid and vapor flow through channels with and without healing and area changes; a heated two-phase test bundle representative of BWR core conditions; and a single-loop PWR model
Measurement of non-steady-state free fatty acid turnover
The accuracy of non-steady-state equations for measuring changes in free fatty acid rate of appearance (Ra) is unknown. In the present study, endogenous lipolysis (traced with [14C]-linoleate) was pharmacologically suppressed in six conscious mongrel dogs. A computer-responsive infusion pump was then used to deliver an intravenous oleic acid emulsion in both constant and linear gradient infusion modes. Both non-steady-state equations with various effective volumes of distribution (V) and steady-state equations were used to measure oleate Ra [(14C]oleate). Endogenous lipolysis did not change during the experiment. When oleate Ra increased in a linear gradient fashion, only non-steady-state equations with a large (150 ml/kg) V resulted in erroneous values (9% overestimate, P less than 0.05). In contrast, when oleate Ra decreased in a similar fashion, steady-state and standard non-steady-state equations (V = plasma volume = 50 ml/kg) overestimated total oleate Ra (18 and 7%, P less than 0.001 and P less than 0.05, respectively). Overall, non-steady-state equations with an effective V of 90 ml/kg (1.8 x plasma volume) allowed the most accurate estimates of oleate Ra
Measurement of non-steady-state free fatty acid turnover
Jensen, M.D.; Heiling, V.; Miles, J.M. (Mayo Clinic, Rochester, MN (USA))
1990-01-01
The accuracy of non-steady-state equations for measuring changes in free fatty acid rate of appearance (Ra) is unknown. In the present study, endogenous lipolysis (traced with ({sup 14}C)-linoleate) was pharmacologically suppressed in six conscious mongrel dogs. A computer-responsive infusion pump was then used to deliver an intravenous oleic acid emulsion in both constant and linear gradient infusion modes. Both non-steady-state equations with various effective volumes of distribution (V) and steady-state equations were used to measure oleate Ra (({sup 14}C)oleate). Endogenous lipolysis did not change during the experiment. When oleate Ra increased in a linear gradient fashion, only non-steady-state equations with a large (150 ml/kg) V resulted in erroneous values (9% overestimate, P less than 0.05). In contrast, when oleate Ra decreased in a similar fashion, steady-state and standard non-steady-state equations (V = plasma volume = 50 ml/kg) overestimated total oleate Ra (18 and 7%, P less than 0.001 and P less than 0.05, respectively). Overall, non-steady-state equations with an effective V of 90 ml/kg (1.8 x plasma volume) allowed the most accurate estimates of oleate Ra.
A Note on Equations for Steady-State Optimal Landscapes
Liu, H.H.
2010-06-15
Based on the optimality principle (that the global energy expenditure rate is at its minimum for a given landscape under steady state conditions) and calculus of variations, we have derived a group of partial differential equations for describing steady-state optimal landscapes without explicitly distinguishing between hillslopes and channel networks. Other than building on the well-established Mining's equation, this work does not rely on any empirical relationships (such as those relating hydraulic parameters to local slopes). Using additional constraints, we also theoretically demonstrate that steady-state water depth is a power function of local slope, which is consistent with field data.
Allen, Micah; Smallwood, Jonathan; Christensen, Joanna;
2013-01-01
Self-generated thoughts unrelated to ongoing activities, also known as "mind-wandering," make up a substantial portion of our daily lives. Reports of such task-unrelated thoughts (TUTs) predict both poor performance on demanding cognitive tasks and blood-oxygen-level-dependent (BOLD) activity in......-wandering on response inhibition and monitoring, using the Error Awareness Task (EAT). We expected to replicate links between TUT and reduced inhibition, and explored whether variance in TUT would predict improved error monitoring, reflecting a capacity to balance between internal and external cognition. By...... during error awareness, supporting a link between monitoring and TUTs. Altogether our results suggest that although TUT is detrimental to task performance, fluctuations in attention between self-generated and external task-related thought is a characteristic of individuals with greater metacognitive...
Steady state operation using improved ICH antenna and ECH for high performance plasma in LHD
The steady state operation (SSO) of high-performance plasma in LHD has progressed since the last IAEA conference by means of a newly installed ICH antenna (HAS antenna) and an improved ECH system. HAS antenna could control the launched parallel wave number and heated a core plasma efficiently. Understanding of the physics and technology of wave heating, particle and heat flow balances, and plasma wall interaction have also improved in LHD in recent years. The heating power of steady state ICH and ECH exceeded 1 MW and 500 kW, respectively, and the higher-density helium plasma with minority hydrogen ions was maintained by using the HAS antenna and new 77 GHz gyrotrons. As a result, plasma performance improved; e.g., an electron temperature of more than 2 keV at a density of more than 2 x 1019 m-3 became possible for more than 1 min. Heat flow balance and particle flux balance of steady-state operation are evaluated. Particle balance analysis indicates that externally fed helium and hydrogen particles are mainly absorbed by a chamber wall and divertor plates, even after the 54-min operation. (author)
Enhancement of the steady-state magnetization in TROSY experiments
Under the condition that the longitudinal relaxation time of spin I is shorter than the longitudinal relaxation time of spin S the steady-state magnetization in [S,I]-TROSY-type experiments can be enhanced by intermediate storage of a part of the steady-state magnetization of spin I on spin S with a pulse sequence element during the relaxation delay. It is demonstrated with samples ranging in size from the 1 kDa cyclosporin to the 110 kDa 15N,2H-labeled dihydroneopterin Aldolase that intermediate storage of steady-state magnetization in a [15N,1H]-TROSY experiment yields a signal gain of 10-25%. The method proposed here for intermediate storage of steady-state magnetization can be implemented in any [15N,1H]-TROSY-type experiments
Elimination of thermodynamically infeasible loops in steady-state metabolic models.
Schellenberger, Jan; Lewis, Nathan E; Palsson, Bernhard Ø
2011-02-01
The constraint-based reconstruction and analysis (COBRA) framework has been widely used to study steady-state flux solutions in genome-scale metabolic networks. One shortcoming of current COBRA methods is the possible violation of the loop law in the computed steady-state flux solutions. The loop law is analogous to Kirchhoff's second law for electric circuits, and states that at steady state there can be no net flux around a closed network cycle. Although the consequences of the loop law have been known for years, it has been computationally difficult to work with. Therefore, the resulting loop-law constraints have been overlooked. Here, we present a general mixed integer programming approach called loopless COBRA (ll-COBRA), which can be used to eliminate all steady-state flux solutions that are incompatible with the loop law. We apply this approach to improve flux predictions on three common COBRA methods: flux balance analysis, flux variability analysis, and Monte Carlo sampling of the flux space. Moreover, we demonstrate that the imposition of loop-law constraints with ll-COBRA improves the consistency of simulation results with experimental data. This method provides an additional constraint for many COBRA methods, enabling the acquisition of more realistic simulation results. PMID:21281568
Steady-state current transfer and scattering theory
Ben-Moshe, Vered; Rai, Dhurba; Skourtis, Spiros S.; Nitzan, Abraham
2010-01-01
The correspondence between the steady state theory of current transfer and scattering theory in a system of coupled tight-binding models of 1-dimensional wires is explored. For weak interwire coupling both calculations give nearly identical results, except at singular points associated with band edges. The effect of decoherence in each of these models is studied using a generalization of the Liouville-von Neuman equation suitable for steady-state situations. An example of a single impurity mo...
Steady-state leaching of tritiated water from silica gel
Das, H.A.; Hou, Xiaolin
2009-01-01
Aqueous leaching of tritium from silica gel, loaded by absorption of water vapor, makes part of reactor de-commissioning. It is found to follow the formulation of steady-state diffusion.......Aqueous leaching of tritium from silica gel, loaded by absorption of water vapor, makes part of reactor de-commissioning. It is found to follow the formulation of steady-state diffusion....
TRANSIENT AND STEADY-STATE DYNAMICS OF GRANULAR SHEAR FLOWS
Losert, W.; Kwon, G.
2001-01-01
The initiation and steady-state dynamics of granular shear flow are investigated experimentally in a Couette geometry with independently moveable outer and inner cylinders. The motion of particles on the top surface is analyzed using fast imaging. During steady state rotation of both cylinders at different rates, a shear band develops close to the inner cylinder for all combinations of speeds of each cylinder we investigated. Experiments on flow initiation were carried out with one of the cyl...
Thermodynamic Study of a Low Temperature Difference Stirling Engine at Steady State Operation
Martaj, Nadia; Rochelle, Pierre; Grosu, Lavinia
2007-01-01
In the current energy economy context, the use of renewable energies and the valuation of lost energies are the subject of many studies. From this point of view, the Stirling engine draws attention of the researchers for its many advantages. This paper presents a thermodynamic analysis of a low temperature Stirling engine at steady state operation; energy, entropy and exergy balances being presented at each main element of the engine. A zero dimensional numerical model describing the variable...
A steady-state F-region model and its use for satellite data analysis
S. M. Stankov
1996-06-01
Full Text Available A steady-state mathematical model of the Earth's upper ionosphere and plasmasphere is presented. In the model the equations of continuity, momentum, and energy balance for O+, H+, and He+ ions are solved numerically along dipole magnetic field lines. As an extension of the model, a searching method is developed for de- termination of the boundary values in a self-consistent manner. Model results are compared with Atmosphere Explorer satellite measurements.
Lake contamination models for evolution towards steady state
Johan C. VAREKAMP
2003-09-01
Full Text Available Most lakes are in an average steady state for water but contaminants may not yet have reached steady state or are gradually being flushed out in a clean-up program. The evolution towards steady state for fully mixed or stratified lakes can be described by basic equations of mass flow. The time-concentration paths for fully mixed lakes are asymptotic toward a steady state concentration, which is reached in about 6 contaminant residence times (and clean-up also takes about 6 residence times. Stratified lakes also evolve towards a whole-lake steady state concentration but show oscillating patterns of concentration versus time, with the amplitude and dampening period depending on the volume ratio of epilimnion to total lake volume. In most natural lakes, the compositional contrast between epilimnion and hypolimnion will become almost erased in 2-4 residence times. An acid lake in North-Patagonia is used as an example of contamination of a thermally stratified lake by volcanic effluents.
An equation oriented approach to steady state flowsheeting of methanol synthesis loop
An equation-oriented approach was developed for steady state flowsheeting of a commercial methanol plant. The loop consists of fixed bed reactor, flash separator, preheater, coolers, and compressor. For steady sate flowsheeting of the plant mathematical model of reactor and other units are needed. Reactor used in loop is a Lurgi type and its configuration is rather complex. Previously reactor and flash separator are modeled as two important units of plant. The model is based on mass and energy balances in each equipment and utilizing some auxiliary equations such as rate of reaction and thermodynamics model for activity coefficients of liquid. In order to validate the mathematical model for the synthesis loop, some simulation data were performed using operating conditions and characteristics of the commercial plant. The good agreement between the steady state simulation results and the plant data shows the validity of the model
Nonequilibrium steady states in fluids of platelike colloidal particles
Bier, Markus; van Roij, René
2008-02-01
Nonequilibrium steady states in an open system connecting two reservoirs of platelike colloidal particles are investigated by means of a recently proposed phenomenological dynamic density functional theory [M. Bier and R. van Roij, Phys. Rev. E 76, 021405 (2007)]. The platelike colloidal particles are approximated within the Zwanzig model of restricted orientations, which exhibits an isotropic-nematic bulk phase transition. Inhomogeneities of the local chemical potential generate a diffusion current which relaxes to a nonvanishing value if the two reservoirs coupled to the system sustain different chemical potentials. The relaxation process of initial states towards the steady state turns out to comprise two regimes: a smoothening of initial steplike structures followed by an ultimate relaxation of the slowest diffusive mode. The position of a nonequilibrium interface and the particle current of steady states depend nontrivially on the structure of the reservoirs due to the coupling between translational and orientational degrees of freedom of the fluid.
Stable MIMO Constrained Predictive Control with Steady state Objective Optimization
无
2000-01-01
A two-stage multi-objective optimization model-predictive control algorithms(MPC) strategy is pre sented. A domain MPC controller with input constraints is used to increase freedom for steady-state objective and enhance stabilization of the controller. A steady-state objective optimization algorithm oriented to transient process is adopted to realize optimization of objectives else than dynamic control. It is proved that .the stabilization for both dynamic control and steady-state objective optimization can be guaranteed. The theoretical results are demonstrated and discussed using a distillation tower as the model. Theoretical analysis and simulation results show that this control strategy is efficient and provides a good strategic solution to practical process control.
From Steady-State To Cyclic Metal Forming Processes
Montmitonnet, Pierre
2007-05-01
Continuous processes often exhibit a high proportion of steady state, and have been modeled with steady-state formulations for thirty years, resulting in very CPU-time efficient computations. On the other hand, incremental forming processes generally remain a challenge for FEM software, because of the local nature of deformation compared with the size of the part to be formed, and of the large number of deformation steps needed. Among them however, certain semi-continuous metal forming processes can be characterized as periodic, or cyclic. In this case, an efficient computational strategy can be derived from the ideas behind the steady-state models. This will be illustrated with the example of pilgering, a seamless tube cold rolling process.
Avoiding Rebound through a Steady-State Economy
Nørgaard, Jørgen
conditions in many parts of the world, the transition towards a steady-state economy needs to begin first in the affluent countries, including the Nordic countries from where most of the information in this chapter is drawn. The politicians in these countries are not seeking a steady-state economy, but some...... only buy some time. From this perspective, the environmental problem with the rebound effect is not the higher energy efficiency, which pushes towards lower flows of resources through the economy, but rather the conventional economy which rebounds the savings, because of its quest for higher flows. In...... this chapter, I shall take the rebound debate further by discussing the possible role of energy efficiency in a sustainable economy that is based on the notion of ‘sufficiency’. The assumption is that globally we need to achieve a ‘steady-state economy’. Considering the urgent need for better material...
Free Boundary Problem of Ono—steady State Seepage Flow
XiaomingGUO; Ying－SUN; 等
1999-01-01
Along with the vigorous developing construction,the number of various underground engineerings is greatly increasing,Such as:the foundations of dams and high-rise multistoried houses,subways and tunnels,water and oil wells etc., where the close attention is always payed to the seepage behaviour in the media around the strutures.The Variatonal Inequality formulation and its FEM solution for the free boundary problem of 2D steady state seepage flow was given by the authors,In this paper a further investigation is made on the non-steady state seepage problem,taken the seepage flow of wells as an example.The presented approach-Variational Inequality and its FEM solution-is also very beneficial to the non-steady state problems,where the transient free boundary can also be defined directly without conventional iterations.
Thermalization of Starlight in the Steady-State Cosmology
Ibison, M
2009-01-01
We investigate the fate of starlight in the Steady-State Cosmology. We discover that it is largely unaffected by the presence of ions in intergalactic space as it gets progressively red-shifted from the visible all the way down to the plasma frequency of the intergalactic matter. At that point, after about 450 Gyr - and contrary to previously published claims - the radiation will be thermalized. Under the assumptions adopted by Gold, Bondi, Hoyle, Narlikar, Burbidge and others concerning the creation of matter in the Steady-State Cosmology, and using reasonable estimates for the baryonic mass-density and mass-fraction of 4He, the analysis predicts a universal radiation field matching the CMB, i.e. having a black-body spectrum and temperature of about 2.7 K. The Steady-state Cosmology predicts that this radiation field will appear to originate from the intergalactic plasma.
Steady State Advanced Tokamak (SSAT): The mission and the machine
Extending the tokamak concept to the steady state regime and pursuing advances in tokamak physics are important and complementary steps for the magnetic fusion energy program. The required transition away from inductive current drive will provide exciting opportunities for advances in tokamak physics, as well as important impetus to drive advances in fusion technology. Recognizing this, the Fusion Policy Advisory Committee and the US National Energy Strategy identified the development of steady state tokamak physics and technology, and improvements in the tokamak concept, as vital elements in the magnetic fusion energy development plan. Both called for the construction of a steady state tokamak facility to address these plan elements. Advances in physics that produce better confinement and higher pressure limits are required for a similar unit size reactor. Regimes with largely self-driven plasma current are required to permit a steady-state tokamak reactor with acceptable recirculating power. Reliable techniques of disruption control will be needed to achieve the availability goals of an economic reactor. Thus the central role of this new tokamak facility is to point the way to a more attractive demonstration reactor (DEMO) than the present data base would support. To meet the challenges, we propose a new ''Steady State Advanced Tokamak'' (SSAT) facility that would develop and demonstrate optimized steady state tokamak operating mode. While other tokamaks in the world program employ superconducting toroidal field coils, SSAT would be the first major tokamak to operate with a fully superconducting coil set in the elongated, divertor geometry planned for ITER and DEMO
Steady-state and transient wellbore temperatures during drilling
McDonald, W.J.
1976-05-20
An extensive literature search was made to locate technical publications and computer programs relating to wellbore temperatures during drilling operations. The search confirmed the need for knowledge of transient and steady state circulating temperatures in the design of geothermal bits. Two approaches were used in calculating borehole temperatures. The steady state solution of Holmes and Swift was programmed and 2100 cases calculated for various borehole configurations. For transient temperature studies, calculations were made for ten borehole configurations. These calculations help emphasize the need for better high temperature bit performance and improved engineering procedures in drilling. The conclusions and recommendations are based on latest available technology for calculating wellbore temperatures.
Correlation Between Steady State and Impulse Earth Resistance Values
N. M. Nor
2009-01-01
Full Text Available This study presented experimental results of earthing systems under low-magnitude currents and under high impulse currents. The details of the measuring circuit involved for both types of testing were described. Three field sites were selected. At each site, three earth electrodes configurations were used. This makes up to nine earthing systems. From both low magnitude and impulse tests, the correlation between the steady state earth resistance value and the earth resistance under fast impulse currents can be observed. The relation between the calculated and measured steady state earth resistance is also shown in this study.
Steady-state entanglement activation in optomechanical cavities
Farace, Alessandro; Ciccarello, Francesco; Fazio, Rosario; Giovannetti, Vittorio
2014-02-01
Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.
Electric machines steady state, transients, and design with Matlab
Boldea, Ion
2009-01-01
Part I: Steady StateIntroductionElectric Energy and Electric MachinesBasic Types of Transformers and Electric MachinesLosses and EfficiencyPhysical Limitations and RatingsNameplate RatingsMethods of AnalysisState of the Art and Perspective Electric TransformersAC Coil with Magnetic Core and Transformer Principles Magnetic Materials in EMs and Their LossesElectric Conductors and Their Skin EffectsComponents of Single- and 3-Phase TransformersFlux Linkages and Inductances of Single-Phase TransformersCircuit Equations of Single-Phase Transformers With Core LossesSteady State and Equivalent Circui
Influence of the epithermal effects on the MCF steady state
This work is devoted to the correct interpretation of the steady-state parameters of the muon catalyzed fusion (MCF) process in a D/T mixture. Previously the influence of the epithermal effects (dtμ-molecule formation by 'hot', non-thermalized tμ atoms) on the steady-state parameters was studied only for measurements with a low-density target (density φ=0.01 relative to the liquid hydrogen density). We suggest a new method allowing direct determination of the necessary corrections to the MCF cycling rate for high-density data (φ≥0.4)
On the steady states of weakly reversible chemical reaction networks
Deng, Jian; Jones, Christopher; Feinberg, Martin; Nachman, Adrian
2011-01-01
A natural condition on the structure of the underlying chemical reaction network, namely weak reversibility, is shown to guarantee the existence of an equilibrium (steady state) in each positive stoichiometric compatibility class for the associated mass-action system. Furthermore, an index formula is given for the set of equilibria in a given stoichiometric compatibility class.
Optimising performance in steady state for a supermarket refrigeration system
Green, Torben; Kinnaert, Michel; Razavi-Far, Roozbeh; Izadi-Zamanabadi, Roozbeh; Niemann, Hans Henrik
Using a supermarket refrigeration system as an illustrative example, the paper postulates that by appropriately utilising knowledge of plant operation, the plant wide performance can be optimised based on a small set of variables. Focusing on steady state operations, the total system performance is...
Plasticity, Fracture and Friction in Steady-State Plate Cutting
Simonsen, Bo Cerup; Wierzbicki, Tomasz
1997-01-01
A closed form solution to the problem of steady-state wedge cutting through a ductile metal plate is presented. The considered problem is an idealization of a ship bottom raking process, i.e. a continuous cutting damage of a ship bottom by a hard knife-like rock in a grounding event. A new...
Plasticity, Fracture and Friction in Steady-State Plate Cutting
Simonsen, Bo Cerup; Wierzbicki, Tomasz
1997-01-01
A closed form solution to the problem of steady-state wedge cutting through a ductile metal plate is presented. The considered problem is an idealization of a ship bottom raking process, i.e. a continuous cutting damage of a ship bottom by a hard knife-like rock in a grounding event. A new kinema...
SBWR Model for Steady-State and Transient Analysis
Gilberto Espinosa-Paredes; Alejandro Nuñez-Carrera
2008-01-01
This paper presents a model of a simplified boiling water reactor (SBWR) to analyze the steady-state and transient behavior. The SBWR model is based on approximations of lumped and distributed parameters to consider neutronics and natural circulation processes. The main components of the model are vessel dome, downcomer, lower plenum, core (ch...
Dark Entangled Steady States of Interacting Rydberg Atoms
Dasari, Durga; Mølmer, Klaus
2013-01-01
their short-lived excited states lead to rapid, dissipative formation of an entangled steady state. We show that for a wide range of physical parameters, this entangled state is formed on a time scale given by the strengths of coherent Raman and Rabi fields applied to the atoms, while it is only weakly...
A displacement based FE formulation for steady state problems
Yu, Yuhong
2005-01-01
In this thesis a new displacement based formulation is developed for elasto-plastic deformations in steady state problems. In this formulation the displacements are the primary variables, which is in contrast to the more common formulations in terms of the velocities as the primary variables. In a s
Steady-State Pharmacokinetics of Bupropion SR in Juvenile Patients
Daviss, W. Burleson; Perel, James M.; Rudolph, George R.; Axelson, David A.; Gilchrist, Richard; Nuss, Sharon; Birmaher, Boris; Brent, David A.
2005-01-01
Objective: To examine the steady-state pharmacokinetic properties of bupropion sustained release (SR) and their potential developmental differences in youths. Method: Eleven boys and eight girls aged 11 to 17 years old were prescribed bupropion SR monotherapy for attention-deficit/hyperactivity disorder (n = 16) and/or depressive disorders (n =…
Combined Steady-State and Dynamic Heat Exchanger Experiment
Luyben, William L.; Tuzla, Kemal; Bader, Paul N.
2009-01-01
This paper describes a heat-transfer experiment that combines steady-state analysis and dynamic control. A process-water stream is circulated through two tube-in-shell heat exchangers in series. In the first, the process water is heated by steam. In the second, it is cooled by cooling water. The equipment is pilot-plant size: heat-transfer areas…
Extending the quasi-steady state approximation by changing variables
Borghans, J.A.M.; Boer, R.J. de; Segel, L.A.
1996-01-01
The parameter domain for which the quasi-steady state assumption is valid can be considerably extended merely by a simple change of variable. This is demonstrated for a variety of biologically significant examples taken from enzyme kinetics, immunology and ecology.
Steady state nutrition by transpiration controlled nutrient supply
Braakhekke, W.G.; Labe, D.A.
1990-01-01
Programmed nutrient addition with a constant relative addition rate has been advocated as a suitable research technique for inducing steady state nutrition in exponentially growing plants. Transpiration controlled nutrient supply is proposed as an alternative technique for plants with a short or no
Analysis of steady-state hydraulic tests in fractured rock
A model for the analysis of steady-state hydraulic injection tests into single fractures of a rock-mass is presented, and solved analytically. It is used to obtain a probability distribution for the transmissivities of fractures in Cornish granite. (author)
The diffusion equation and the steady state. Chapter 2
We shall now study the equations that govern the neutron field in a reactor. These equations are based on the concept of local neutron balance, which takes into account the reaction rates in an element of volume and the net leakage rates out of the volume. The reaction rates are written in terms of the local cross sections, assumed known from a preprocessed database (e.g., ENDF/B-VI). The starting equation is the Maxwell-Boltzmann transport equation, in its integro-differential form. The various approximations required to go from the transport equation to the neutron diffusion equation will be presented first, because all finite-reactor calculations are based on the diffusion approximation. We shall then discuss the multi-group formalism of the diffusion equations and study the mathematical properties of this equation in steady state. This preliminary step will allow us to derive in a more accurate way, in the next chapter, the reactor point-kinetics equations. In the diffusion approximation, neutrons diffuse from regions of high concentration to regions of low concentration, just as heat diffuses from regions of high temperature to those of low temperature, or, rather, as gas molecules diffuse to reduce spatial variations in concentration. While it is sufficiently accurate to treat the transport of gas molecules as a diffusion process, this approach is too limiting for neutron transport. In contrast to a gas, where collisions are very frequent, the cross sections for the interaction of neutrons with nuclei are relatively small, as we saw in chapter 1 (of the order of barns, i.e., 10-24cm2) . This implies that neutrons traverse appreciable distances (of the order of a centimetre) between collisions. This relatively long neutron mean free path, together with the heterogeneity of the physical medium, requires that a more complete treatment be carried out, taking account of variations in the angular distribution of neutron speed in the vicinity of highly absorbing
Steady state operation of MW heating power using ICH and ECH in LHD
Full text of publication follows. The steady-state operation (SSO) of high-performance plasma in the Large Helical Device (LHD) has been progressed steadily by increased heating power of more than 1 MW using ICH and ECH. In the 2012 year campaign, plasma performance of steady state operation was improved to higher density and temperature of 1*1019 m-3 and 2.5 keV for during 20 min. Plasma is sustained by newly installed ICH antenna (HAS antenna which can control the launching parallel wave number) and also using new gyrotron tubes of 77 GHz frequency. The higher wave number operation with dipole phasing of HAS antenna can sustain the higher density plasma steadily in comparison with monopole phasing operation. Typical plasma parameters of long pulse operation of around 20 minutes have been obtained. Bulk ions are helium and minority ion of ICRF heating mode is hydrogen. ECH of 77 GHz frequency is located at plasma center. The radial profiles of electron temperature and density of similar SSO plasma have also been obtained. SSO plasmas are terminated by various reasons. Major reason is arcing occurred inside the ICRF antennas. Local hot spots and erosions of divertor carbon plates are also observed. Particle and heat balances, behaviors of dust and flakes which also frequently terminate the steady state operations are studied and will be presented at the meeting. (authors)
The Steady State Calculation for SMART with MIDAS/SMR
KAERI is developing a new concept of reactor that all the main components such as the steam generator, the coolant pumps and the pressurizer are located inside the reactor vessel. Before the severe accident sequences are estimated, it is prerequisite that MIDAS code predicts the steady state conditions properly. But MIDAS code does not include the heat transfer model for the helical tube. Therefore, the heat transfer models for the helical tube from TASS/SMR-S were implemented into MIDAS code. To estimate the validity of the implemented heat transfer correlations for the helical tube and the input data, the steady state was recalculated with MIDAS/SMR based on design level 2 and compared with the design values
The Steady State Calculation for SMART with MIDAS/SMR
Park, Jong Hwa; Kim, Dong Ha; Chung, Young Jong; Park, Sun Hee [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Cho, Seong Won [KORTIC, Daejeon (Korea, Republic of)
2010-10-15
KAERI is developing a new concept of reactor that all the main components such as the steam generator, the coolant pumps and the pressurizer are located inside the reactor vessel. Before the severe accident sequences are estimated, it is prerequisite that MIDAS code predicts the steady state conditions properly. But MIDAS code does not include the heat transfer model for the helical tube. Therefore, the heat transfer models for the helical tube from TASS/SMR-S were implemented into MIDAS code. To estimate the validity of the implemented heat transfer correlations for the helical tube and the input data, the steady state was recalculated with MIDAS/SMR based on design level 2 and compared with the design values
Nonequilibrium Steady States of a Stochastic Model System.
Zhang, Qiwei
We study the nonequilibrium steady state of a stochastic lattice gas model, originally proposed by Katz, Lebowitz and Spohn (Phys. Rev. B 28: 1655 (1983)). Firstly, we solve the model on some small lattices exactly in order to see the general dependence of the steady state upon different parameters of the model. Nextly, we derive some analytical results for infinite lattice systems by taking some suitable limits. We then present some renormalization group results for the continuum version of the model via field theoretical techniques, the supersymmetry of the critical dynamics in zero field is also explored. Finally, we report some very recent 3-D Monte Carlo simulation results, which have been obtained by applying Multi-Spin-Coding techniques on a CDC vector supercomputer - Cyber 205 at John von Neumann Center.
Steady-state current transfer and scattering theory.
Ben-Moshe, Vered; Rai, Dhurba; Skourtis, Spiros S; Nitzan, Abraham
2010-08-01
The correspondence between the steady-state theory of current transfer and scattering theory in a system of coupled tight-binding models of one-dimensional wires is explored. For weak interwire coupling both calculations give nearly identical results, except at singular points associated with band edges. The effect of decoherence in each of these models is studied using a generalization of the Liouville-von Neuman equation suitable for steady-state situations. An example of a single impurity model is studied in detail, leading to a lattice model of scattering off target that affects both potential scattering and decoherence. For an impurity level lying inside the energy band, the transmission coefficient diminishes with increasing dephasing rate, while the opposite holds for impurity energy outside the band. The efficiency of current transfer in the coupled wire system decreases with increasing dephasing. PMID:20707524
Theory of minimum dissipation of energy for the steady state
The magnetic configuration of an inductively driven steady-state plasma bounded by a surface (or two adjacent surfaces) on which B·n = 0 is force-free: ∇xB = 2αB, where α is a constant, in time and in space. α is the ratio of the Poynting flux to the magnetic helicity flux at the boundary. It is also the ratio of the dissipative rates of the magnetic energy to the magnetic helicity in the plasma. The spatial extent of the configuration is noninfinitesimal. This global constraint is a result of the requirement that, for a steady-state plasma, the rate of change of the vector potential, ∂A/∂t, is constant in time and uniform in space
Steady-state propagation of interface corner crack
Veluri, Badrinath; Jensen, Henrik Myhre
2013-01-01
Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated by...... estimating the fracture mechanics parameters that includes the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the interface crack front. A numerical approach was then applied for coupling the far field solutions based on the Finite Element Method to the near...... field (crack tip) solutions based on the J-integral. The adopted two-dimensional numerical approach for the calculation of fracture mechanical properties was compared with three-dimensional models for quarter-circular and straight sided crack front shapes. A quantitative approach was formulated based on...
Steady states of the parametric rotator and pendulum
Bouzas, Antonio O
2011-01-01
We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the damped, non-linear equation of motion of the parametric rotator and pendulum perturbatively for small parametric excitation and damping, although our perturbative approach can be extended to other regimes as well. Our treatment involves only ordinary second-order differential equations with constant coefficients, and provides numerically accurate perturbative solutions in terms of elementary functions. Some of the steady-state rotation and oscillation modes studied here have not been discussed in the previous literature. Other well-known ones, such as parametric resonance and the inverted pendulum, are extended to elliptic parametric excitation tilted with respect to gravi...
Master equation based steady-state cluster perturbation theory
Nuss, Martin; Dorn, Gerhard; Dorda, Antonius; von der Linden, Wolfgang; Arrigoni, Enrico
2015-09-01
A simple and efficient approximation scheme to study electronic transport characteristics of strongly correlated nanodevices, molecular junctions, or heterostructures out of equilibrium is provided by steady-state cluster perturbation theory. In this work, we improve the starting point of this perturbative, nonequilibrium Green's function based method. Specifically, we employ an improved unperturbed (so-called reference) state ρ̂S, constructed as the steady state of a quantum master equation within the Born-Markov approximation. This resulting hybrid method inherits beneficial aspects of both the quantum master equation as well as the nonequilibrium Green's function technique. We benchmark this scheme on two experimentally relevant systems in the single-electron transistor regime: an electron-electron interaction based quantum diode and a triple quantum dot ring junction, which both feature negative differential conductance. The results of this method improve significantly with respect to the plain quantum master equation treatment at modest additional computational cost.
Steady State Dynamic Operating Behavior of Universal Motor
Muhammad Khan Burdi
2015-01-01
Full Text Available A detailed investigation of the universal motor is developed and used for various dynamic steady state and transient operating conditions of loads. In the investigation, output torque, motor speed, input current, input/output power and efficiency are computed, compared and analyzed for different loads. While this paper discusses the steady-state behavior of the universal motor, another companion paper, ?Transient dynamic behavior of universal motor?, will discuss its transient behavior in detail. A non-linear generalized electric machine model of the motor is considered for the analysis. This study was essential to investigate effect of output load on input current, power, speed and efficiency of the motor during operations. Previously such investigation is not known
Steady-state Physics, Effective Temperature Dynamics in Holography
Kundu, Arnab
2013-01-01
Using the gauge-gravity duality, we argue that for a certain class of out-of-equilibrium steady-state systems in contact with a heat bath at a given temperature, the macroscopic physics can be captured by an effective thermodynamic description. The steady-state is obtained by applying a constant electric field that results in a stationary current flow. Within holography, we consider generic probe systems where an open string equivalence principle and an open string metric govern the effective thermodynamics. This description comes equipped with an effective temperature, which is larger than the bath temperature, and a corresponding effective entropy. For conformal or scale-invariant theories, certain scaling behaviours follow immediately. In general, in the large electric field limit, this effective temperature is also observed to obey certain generic relations with various physical parameters in the system.
Steady state test on PWR steam generator thermohydraulics
Experimental activity on U-tube steam generator thermal hydraulics is under way at CISE and SIET in the framework of ENEA's LWR safety research programme. The test section includes 9 tubes. Hot side and cold side can be separated simulated, with primary and secondary fluid in full thermalhydraulic conditions. The experimental matrix includes: steady state tests (in both adiabatic and diabatic conditions); transients tests that simulate various accidents. Some steady state tests are reported. The secondary side average density, measured by the quick closing valve technique can be accurately calculated by the Zuber-Dix and Zuber-Rohuani correlations. Continuous pressure drops can be very well predicted by an adapted version of Thom correlation and CISE DIF-3 correlation: the development of an empirical correlation was, instead, necessary for assessment of the local pressure drops across spacer grids
Turnover of messenger RNA: Polysome statistics beyond the steady state
Valleriani, A.; Ignatova, Z.; Nagar, A.; Lipowsky, R.
2010-03-01
The interplay between turnover or degradation and ribosome loading of messenger RNA (mRNA) is studied theoretically using a stochastic model that is motivated by recent experimental results. Random mRNA degradation affects the statistics of polysomes, i.e., the statistics of the number of ribosomes per mRNA as extracted from cells. Since ribosome loading of newly created mRNA chains requires some time to reach steady state, a fraction of the extracted mRNA/ribosome complexes does not represent steady state conditions. As a consequence, the mean ribosome density obtained from the extracted complexes is found to be inversely proportional to the mRNA length. On the other hand, the ribosome density profile shows an exponential decrease along the mRNA for prokaryotes and becomes uniform in eukaryotic cells.
Non-equilibrium steady states for chains of four rotors
Cuneo, Noé; Eckmann, Jean-Pierre
2015-01-01
We study a chain of four interacting rotors (rotators) connected at both ends to stochastic heat baths at different temperatures. We show that for non-degenerate interaction potentials the system relaxes, at a stretched exponential rate, to a non-equilibrium steady state (NESS). Rotors with high energy tend to decouple from their neighbors due to fast oscillation of the forces. Because of this, the energy of the central two rotors, which interact with the heat baths only through the external ...
Steady-State Oscillations in Resonant Electrostatic Vibration Energy Harvesters
Blokhina, Elena; Galayko, Dimitri; Basset, Philippe; Feely, Orla
2013-01-01
In this paper, we present a formal analysis and description of the steady-state behavior of an electrostatic vibration energy harvester operating in constant-charge mode and using different types of electromechanical transducers. The method predicts parameter values required to start oscillations, allows a study of the dynamics of the transient process, and provides a rigorous description of the system, necessary for further investigation of the related nonlinear phenomena and for the optimis...
Simulation of Power Electronic Converters Using Quasi Steady State Approximation
Predrag Pejović
2012-01-01
A new method to compute voltage and current waveforms of power electronic converters is proposed in the paper. The method relies on simulation result of averaged circuit model, and superimposes the ripple of the inductor currents to the obtained average values, assuming that the linear ripple approximation applies. To determine the amplitude of the switching ripple, a quasi steady state approximation is proposed. After the inductor currents are obtained, currents of switching components are c...
Steady State Plasma Accelerators and their Applications in Thermonuclear Research
Steady state plasma accelerators make it possible in principle to obtain plasma fluxes of high energy and large flow rate. This is of interest in thermonuclear research for two reasons. Firstly, the accelerator can be used for injecting plasma into existing traps; secondly, it can be used to design new-types of thermonuclear reactors, which might be referred to as, ''Flow-type Reactors'' in which a positive yield is-realised during the time the material passes through the reactor system. The main types of accelerating mechanisms operating in this accelerator are described and a brief review is given of theoretical, numerical and experimental investigations carried out by the author and his colleagues. The numerical and theoretical analysis of the processes taking place in coaxial steady state accelerators revealed the possible existence of steady-state compressive flows during which the applied electromagnetic energy is not converted into kinetic plasma energy but is used for compression of the plasma. When the compressed flow is allowed to expand its thermal energy is converted into kinetic energy. Devices in which compressive flow is attained are referred to as magnetic plasma compressors. At the present stage the existence of compressive flows has been confirmed experimentally. To ensure a positive yield in-the region of compression a density of 1020 - 1020 cm-3 is essential. The possibility of obtaining a positive yield in linear ''Flow type Reactors'' is discussed. Such reactors consist of magnetic plasma guides of length ∼ 100 m, in which a flow of hot plasma is produced by a steady state plasma accelerator. (author)
Towards steady-state tokamak operation with double transport barriers
Internal Transport Barriers characteristic for the Optimised Shear regime and an edge transport barrier of an ELMy H-mode regime have been superposed in the Double Barrier mode. In DT discharges the Double Barrier mode has resulted in 50% higher fusion power output and a factor 2 higher fusion gain Q than in conventional sawtoothing steady-state ELMy H-mode plasmas. Steady-state conditions in temperature and density profiles have been approached in Double Barrier discharges in deuterium. The Double Barrier mode has been routinely established in the new Gas Box divertor configuration on JET. Off-axis LHCD has been used for current profile control during the high performance phase. In preparation of a new DTE2 campaign on JET the potential of the Double Barrier mode for sustained high fusion performance has been explored in modelling studies. Steady-state operation on ITER has been studied in transport code modelling for Advanced Tokamak scenarios in the Double Barrier mode. (author)
Transient and steady-state currents in epoxy resin
Guillermin, Christophe [Schneider Electric Industries S.A.S., 37 quai Paul-Louis Merlin, 38050 Grenoble Cedex 9 (France); Rain, Pascal [Laboratoire d' Electrostatique et de Materiaux Dielectriques (LEMD), CNRS, 25 avenue des Martyrs, 38042 Grenoble Cedex 9 (France); Rowe, Stephen W [Schneider Electric Industries S.A.S., 37 quai Paul-Louis Merlin, 38050 Grenoble Cedex 9 (France)
2006-02-07
Charging and discharging currents have been measured in a diglycidyl ether of bisphenol-A epoxy resin with and without silica fillers, below and above its glass transition temperature T{sub g} = 65 deg. C. Both transient and steady-state current densities have been analysed. The average applied fields ranged from 3 to 35 kV mm{sup -1} with a sample thickness of 0.5 mm. Above T{sub g}, transient currents suggested a phenomenon of charge injection forming trapped space charges even at low fields. Steady-state currents confirmed that the behaviour was not Ohmic and suggested Schottky-type injection. Below T{sub g}, the current is not controlled by the metal-dielectric interface but by the conduction in the volume: the current is Ohmic at low fields and both transient and steady-state currents suggest a phenomenon of space-charge limited currents at high fields. The field threshold is similar in the filler-free and the filled resin. Values in the range 12-17 kV mm{sup -1} have been measured.
Steady state theta pinch concept for slow formation of FRC
A steady state high beta plasma flow through a channel along the magnetic field increasing downstream can be regarded as a ''steady state theta pinch'', because if we see the plasma riding on the flow we should observe very similar process taking place in a theta pinch. Anticipating to produce an FRC without using very high voltage technics such as the ones required in a conventional theta pinch, we have studied after the analogy a ''steady state reversed field theta pinch'' which is brought about by steady head-on collision of counter plasma streams along the channel as ejected from two identical co-axial plasma sources mounted at the both ends of the apparatus. The ideal Poisson and shock adiabatic flow models are employed for the analysis of the steady colliding process. It is demonstrated that an FRC involving large numbers of particles is produced only by the weak shock mode which is achieved in case energetic plasma flow is decelerated almost to be stagnated through Poisson adiabatic process before the streams are collided. (author)
Extracting Steady State Components from Synchrophasor Data Using Kalman Filters
Farhan Mahmood
2016-04-01
Full Text Available Data from phasor measurement units (PMUs may be exploited to provide steady state information to the applications which require it. As PMU measurements may contain errors and missing data, the paper presents the application of a Kalman Filter technique for real-time data processing. PMU data captures the power system’s response at different time-scales, which are generated by different types of power system events; the presented Kalman Filter methods have been applied to extract the steady state components of PMU measurements that can be fed to steady state applications. Two KF-based methods have been proposed, i.e., a windowing-based KF method and “the modified KF”. Both methods are capable of reducing noise, compensating for missing data and filtering outliers from input PMU signals. A comparison of proposed methods has been carried out using the PMU data generated from a hardware-in-the-loop (HIL experimental setup. In addition, a performance analysis of the proposed methods is performed using an evaluation metric.
Transient and steady-state currents in epoxy resin
Charging and discharging currents have been measured in a diglycidyl ether of bisphenol-A epoxy resin with and without silica fillers, below and above its glass transition temperature Tg = 65 deg. C. Both transient and steady-state current densities have been analysed. The average applied fields ranged from 3 to 35 kV mm-1 with a sample thickness of 0.5 mm. Above Tg, transient currents suggested a phenomenon of charge injection forming trapped space charges even at low fields. Steady-state currents confirmed that the behaviour was not Ohmic and suggested Schottky-type injection. Below Tg, the current is not controlled by the metal-dielectric interface but by the conduction in the volume: the current is Ohmic at low fields and both transient and steady-state currents suggest a phenomenon of space-charge limited currents at high fields. The field threshold is similar in the filler-free and the filled resin. Values in the range 12-17 kV mm-1 have been measured
SBWR Model for Steady-State and Transient Analysis
Gilberto Espinosa-Paredes
2008-05-01
Full Text Available This paper presents a model of a simplified boiling water reactor (SBWR to analyze the steady-state and transient behavior. The SBWR model is based on approximations of lumped and distributed parameters to consider neutronics and natural circulation processes. The main components of the model are vessel dome, downcomer, lower plenum, core (channel and fuel, upper plenum, pressure, and level controls. Further consideration of the model is the natural circulation path in the internal circuit of the reactor, which governs the safety performance of the SBWR. To demonstrate the applicability of the model, the predictions were compared with plant data, manufacturer_s predictions, and RELAP5 under steady-state and transient conditions of a typical BWR. In steady-state conditions, the profiles of the main variables of the SBWR core such as superficial velocity, void fraction, temperatures, and convective heat transfer coefficient are presented and analyzed. The transient behavior of SBWR was analyzed during the closure of all main steam line isolation valves (MSIVs. Our results in this transient show that the cooling system due to natural circulation in the SBWR is around 70% of the rated core flow. According to the results shown here, one of the main conclusions of this work is that the simplified model could be very helpful in the licensing process.
Small steady-state tokamak (TST) for divertor testing
The TST is a small steady-state tokamak designed for testing diverters under conditions similar to those anticipated in future large tokamaks. An initial design has R0/a = 2.5, R0 = 0.75 m, a = 0.3 m, and Bt0 = 2.2 T with full inductive capability. With heating and current drive power of 4.5 MW, the heat flux at the plasma edge Q perpendicular can be as high as 0.3 MW/m2. Plasma currents Ip above 500 kA can be maintained by 1 MW of lower hybrid power (2.45 GHz) for average densities ne up to 3 x 1019 m-3. Additional power via ICRF (2 MW) and neutral beams (1.5 MW) maintain current for ne up to 5 x 1019 m-3. Fully demountable, actively cooled, steady-state toroidal field coils permit ample access for the auxiliary systems and diverter cassettes. The toroidal field magnets require a steady-state supply of less than 40 MW. The size and cost of the TST can be reduced by eliminating the solenoid, reducing Bt0 to 1.4 T, and lowering R0/a to 1.7. This option permits low-R0/a experimentation while maintaining the capability for testing divertors but requires successful noninductive current initiation and maintenance in the low-R0/a regime
Steady state free radical budgets and ozone photochemistry during TOPSE
Cantrell, Christopher A.; Mauldin, L.; Zondlo, M.; Eisele, F.; Kosciuch, E.; Shetter, R.; Lefer, B.; Hall, S.; Campos, T.; Ridley, B.; Walega, J.; Fried, A.; Wert, B.; Flocke, F.; Weinheimer, A.; Hannigan, J.; Coffey, M.; Atlas, E.; Stephens, S.; Heikes, B.; Snow, J.; Blake, D.; Blake, N.; Katzenstein, A.; Lopez, J.; Browell, E. V.; Dibb, J.; Scheuer, E.; Seid, G.; Talbot, R.
2003-02-01
A steady state model, constrained by a number of measured quantities, was used to derive peroxy radical levels for the conditions of the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign. The analysis is made using data collected aboard the NCAR/NSF C-130 aircraft from February through May 2000 at latitudes from 40° to 85°N, and at altitudes from the surface to 7.6 km. HO2 + RO2 radical concentrations were measured during the experiment, which are compared with model results over the domain of the study showing good agreement on the average. Average measurement/model ratios are 1.04 (σ = 0.73) and 0.96 (σ = 0.52) for the MLB and HLB, respectively. Budgets of total peroxy radical levels as well as of individual free radical members were constructed, which reveal interesting differences compared to studies at lower latitudes. The midlatitude part of the study region is a significant net source of ozone, while the high latitudes constitute a small net sink leading to the hypothesis that transport from the middle latitudes can explain the observed increase in ozone in the high latitudes. Radical reservoir species concentrations are modeled and compared with the observations. For most conditions, the model does a good job of reproducing the formaldehyde observations, but the peroxide observations are significantly less than steady state for this study. Photostationary state (PSS) derived total peroxy radical levels and NO/NO2 ratios are compared with the measurements and the model; PSS-derived results are higher than observations or the steady state model at low NO concentrations.
Small steady-state tokamak (TST) for divertor testing
Peng, Y.M.; Colchin, R.J.; Swain, D.W.; Nelson, B.E.; Monday, J.F. (Oak Ridge National Lab., TN (United States)); Blevins, J.; Delisle, M.; Stringer, J. (Canadian Fusion Fuels Technology Project, Mississauga, ON (Canada)); Bonoli, P.; Luckhardt, S. (Massachusetts Inst. of Tech., Cambridge, MA (United States)); Pauletti, R. (Sao Paulo Univ., SP (Brazil))
1992-01-01
The TST is a small steady-state tokamak designed for testing diverters under conditions similar to those anticipated in future large tokamaks. An initial design has R{sub 0}/a = 2.5, R{sub 0} = 0.75 m, a = 0.3 m, and Bt{sub 0} = 2.2 T with full inductive capability. With heating and current drive power of 4.5 MW, the heat flux at the plasma edge Q{perpendicular} can be as high as 0.3 MW/m{sup 2}. Plasma currents I{sub p} above 500 kA can be maintained by 1 MW of lower hybrid power (2.45 GHz) for average densities n{sub e} up to 3 {times} 10{sup 19} m{sup {minus}3}. Additional power via ICRF (2 MW) and neutral beams (1.5 MW) maintain current for n{sub e} up to 5 {times} 10{sup 19} m{sup {minus}3}. Fully demountable, actively cooled, steady-state toroidal field coils permit ample access for the auxiliary systems and diverter cassettes. The toroidal field magnets require a steady-state supply of less than 40 MW. The size and cost of the TST can be reduced by eliminating the solenoid, reducing Bt{sub 0} to 1.4 T, and lowering R{sub 0}/a to 1.7. This option permits low-R{sub 0}/a experimentation while maintaining the capability for testing divertors but requires successful noninductive current initiation and maintenance in the low-R{sub 0}/a regime.
Steady-state Compartmentalization of Lipid Membranes by Active Proteins
Sabra, Mads Christian; Mouritsen, Ole G.
1998-01-01
-protein assembly reorganizes into a steady-state structure with a typical length scale determined by the strength of the external drive. In the specific case of a mixed dimyristoylphosphatidylcholine-distearoylphosphatidylcholine bilayer in the gel-fluid coexistence region, it is shown explicitly by computer...... conformational excitations governed by an external drive, and the deexcitation is controlled by interaction of the protein with its lipid surroundings. In response to the flux of energy into the proteins from the environment and the subsequent dissipation of energy into the lipid bilayer, the lipid...
Steady-State Plasmas in KT5D Magnetized Torus
ZHU Zhenhua; LIU Wandong; WAN Baonian; ZHAO Yanping; LI Jiangang; YAN Longwen; YANG Qingwei; DING Xuantong; XU Min; YU Yi; WANG Zhijiang; LU Ronghua; WEN Yizhi; YU Changxuan; MA Jinxiu; WAN Shude
2007-01-01
Steady-state plasma generated by electron cyclotron resonance (ECR) wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.
Steady State of the Dusty Plasma in a dc Discharge
马锦秀; 郁明阳; 梁小平; 郑坚; 刘万东; 俞昌旋
2002-01-01
The steady state formed by the diffusion of plasma particles in an inhomogeneous dusty plasma is investigated theoretically and compared with our previous experimental results /Nucl. Fusion Plasma Phys. 20(2000)180 (in Chinese); Phys. Plasmas 8(2001)1459]. The negatively charged dust grains with an average charge number of the order of 105 on a single grain enhance the plasma inhomogeneity by decreasing the diffusion velocity, and can cause significant depletion of electrons. The theoretical electron density profile is in good agreement with the experiment, and the theoretical profile of the electron-to-ion density ratio is in reasonable agreement with experimentally estimated data.
Long Pulse Operation on Tore-Supra: Towards Steady State
The experimental programme of Tore Supra is devoted to the study of technology and physics issues associated to long-duration high performance discharges. This new domain of operation requires simultaneously and in steady state: heat removal capability, particle exhaust, fully non-inductive current drive, advanced technology integration and real time plasma control. The long discharge allows for addressing new time scale physic such as the wall particle retention and erosion. Moreover, the physics of fully non-inductive discharges is full of novelty, namely: the MHD stability, the slow spontaneous oscillation of the central electron temperature or the outstanding inward particle pinch
Steady-state and transient wellbore temperatures during drilling
McDonald, W.J.
1976-05-20
An extensive literature search was made to locate technical publications and computer programs relating to wellbore temperatures during drilling operations. Publications obtained are listed in the References. Two approaches were used in calculating borehole temperatures: The steady state solution of Holmes and Swift was programmed and 2100 cases calculated for various borehole configurations. For transient temperature studies, Exxon Production Research Co. made calculations for ten borehole configurations under subcontract. These calculations emphasize the need for better high temperature bit performance and improved engineering procedures in drilling.
Literature review: Steady-state modelling of loop heat pipes
Siedel, B.; Sartre, V.; Lefèvre, Frédéric
2015-01-01
Loop heat pipes (LHPs) are efficient and reliable heat transfer systems whose operation is based on the liquid–vapour phase-change phenomenon. They use the capillary pressure generated in a porous structure to passively circulate the fluid from a heat source to a heat sink. In this paper, an exhaustive literature review is carried out in order to investigate the existing steady-state models of LHPs. These models can be divided into three categories: numerical models of the entire system, nume...
Analysis of steady-state ductile crack growth
Niordson, Christian
1999-01-01
The fracture strength under quasi-static steady-state crack growth in an elastic-plastic material joined by a laser weld is analyzed. Laser welding gives high mismatch between the yield stress within the weld and the yield stress in the base material. This is due to the fast termic cycle, which the...... fracture zone. Both models predict that in general a thinner laser weld gives higher interface strength. Furthermore, both fracture criteria show, that the preferred path of the crack is close outside the weld material; a phenomenon also observed in experiments....
Steady-state organization of binary mixtures by active impurities
Sabra, Mads Christian; Gilhøj, Henriette; Mouritsen, Ole G.
1998-01-01
The structural reorganization of a phase-separated binary mixture in the presence of an annealed dilution of active impurities is studied by computer-simulation techniques via a simple two-dimensional lattice-gas model. The impurities, each of which has two internal states with different affinity...... for the two species, become active by an external driving of a transition between the two impurity states, leading to an energy flow from the impurities into the binary mixture. In steady state, the drive is found to break down the phase-separated state and lead to a new finite length scale controlled...
Skewness of steady-state current fluctuations in nonequilibrium systems
Belousov, Roman; Cohen, E. G. D.; Wong, Chun-Shang; Goree, John A.; Feng, Yan
2016-04-01
A skewness of the probability for instantaneous current fluctuations, in a nonequilibrium steady state, is observed experimentally in a dusty plasma. This skewness is attributed to the spatial asymmetry, which is imminent to the nonequilibrium systems due to the external hydrodynamic gradient. Using the modern framework of the large deviation theory, we extend the Onsager-Machlup ansatz for equilibrium fluctuations to systems with a preferred spatial direction, and provide a modulated Gaussian probability distribution, which is tested by simulations. This probability distribution is also of potential interest for other statistical disciplines. Connections with the principles of statistical mechanics, due to Boltzmann and Gibbs, are discussed as well.
Quantum-classical correspondence in steady states of nonadiabatic systems
We first present nonadiabatic path integral which is exact formulation of quantum dynamics in nonadiabatic systems. Then, by applying the stationary phase approximations to the nonadiabatic path integral, a semiclassical quantization condition, i.e., quantum-classical correspondence, for steady states of nonadiabatic systems is presented as a nonadiabatic trace formula. The present quantum-classical correspondence indicates that a set of primitive hopping periodic orbits, which are invariant under time evolution in the phase space of the slow degree of freedom, should be quantized. The semiclassical quantization is then applied to a simple nonadiabatic model and accurately reproduces exact quantum energy levels
Curva de Laffer para Portugal, perspetiva de steady state
Azevedo, Diogo Ricardo Reis
2014-01-01
São analisadas as receitas de imposto sobre o trabalho, consumo e capital, em termos de curva de Laffer, através da aplicação de um modelo neoclássico, especialmente calibrado para a economia Portuguesa, envolvendo o período de tempo de 1995 a 2012. Foi encontrada a evidência, robusta, de curvas de Laffer para a tributação sobre o trabalho e capital. Este estudo concluiu que Portugal tem margem para aumentar impostos, numa perspetiva de steady state, sendo que Portugal pode aumentar a sua rec...
Steady-state capabilities for hydroturbines with OpenFOAM
The availability of a high quality Open Source CFD simulation platform like OpenFOAM offers new R and D opportunities by providing direct access to models and solver implementation details. Efforts have been made by Hydro-Quebec to adapt OpenFOAM to hydroturbines for the development of steady-state capabilities. The paper describes the developments that have been made to implement new turbomachinery related capabilities: Multiple Frame of Reference solver, domain coupling interfaces (GGI, cyclicGGI and mixing plane) and specialized boundary conditions. Practical use of the new turbomachinery capabilities are demonstrated for the analysis of a 195-MW Francis hydroturbine.
Steady states of the parametric rotator and pendulum
Bouzas, Antonio O, E-mail: abouzas@fis.mda.cinvestav.m [Departamento de Fisica Aplicada, CINVESTAV-IPN, Carretera Antigua a Progreso Km. 6, Apdo Postal 73 ' Cordemex' , Merida 97310, Yucatan (Mexico)
2010-11-15
We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the damped, nonlinear equation of motion of the parametric rotator and pendulum perturbatively for small parametric excitation and damping, although our perturbative approach can be extended to other regimes as well. Our treatment involves only ordinary second-order differential equations with constant coefficients, and provides numerically accurate perturbative solutions in terms of elementary functions. Some of the steady-state rotation and oscillation modes studied here have not been discussed in the previous literature. Other well-known ones, such as parametric resonance and the inverted pendulum, are extended to elliptic parametric excitation tilted with respect to gravity. The results presented here should be accessible to advanced undergraduates, and of interest to graduate students and specialists in the field of nonlinear mechanics.
Transient and steady-state selection in the striatal microcircuit
Adam Tomkins
2014-01-01
Full Text Available Although the basal ganglia have been widely studied and implicated in signal processing and action selection, little information is known about the active role the striatal microcircuit plays in action selection in the basal ganglia-thalamo-cortical loops. To address this knowledge gap we use a large scale three dimensional spiking model of the striatum, combined with a rate coded model of the basal ganglia-thalamo-cortical loop, to asses the computational role the striatum plays in action selection. We identify a robust transient phenomena generated by the striatal microcircuit, which temporarily enhances the difference between two competing cortical inputs. We show that this transient is sufficient to modulate decision making in the basal ganglia-thalamo-cortical circuit. We also find that the transient selection originates from a novel adaptation effect in single striatal projection neurons, which is amenable to experimental testing. Finally, we compared transient selection with models implementing classical steady-state selection. We challenged both forms of model to account for recent reports of paradoxically enhanced response selection in Huntington's Disease patients. We found that steady-state selection was uniformly impaired under all simulated Huntington's conditions, but transient selection was enhanced given a sufficient Huntington's-like increase in NMDA receptor sensitivity. Thus our models provide an intriguing hypothesis for the mechanisms underlying the paradoxical cognitive improvements in manifest Huntington's patients.
A steady-state measurement system for total hemispherical emissivity
A steady-state calorimetric technique was developed for measuring the total hemispherical emissivity of a conductive material. The system uses a thin strip of the conductive sample electrically heated by alternating current to high temperatures in a vacuum chamber. The emissivity was measured in a central region of the sample with an approximately uniform temperature distribution. Considering the influences of the gray body assumption, wire heat losses, effects of residual gas and conductive heat loss from the region to the rest of the strip, the emissivity was accurately determined by solving the inverse one-dimension steady-state heat transfer problem. The emissivities of various metal samples (nickel and 45# steel) were measured to verify the system accuracy. And the results were then analyzed to estimate the relative errors of emissivity arising from the gray body assumption, wire heat losses, effects of residual gas, non-uniform temperature distribution and the measurement uncertainty of emissivity. In the temperature range from 700 to 1300 K, the accuracy is acceptable for practical applications within the total measurement uncertainties of 1.1%. To increase the system applicability, some issues related to sample specifications, heating power control and temperature uniformity of sample test section were discussed. Thus, this system can provide accurate measurements of the total hemispherical emissivity of conductive samples at high temperatures. (paper)
Concept study of the Steady State Tokamak Reactor (SSTR)
The Steady State Tokamak Reactor (SSTR) concept has been proposed as a realistic fusion power reactor to be built in the near future. An overall concept of SSTR is introduced which is based on a small extension of the present day physics and technologies. The major feature of SSTR is the maximum utilization of a bootstrap current in order to reduce the power required for the steady state operation. This requirement leads to the choice of moderate current (12 MA), and high βp (2.0) for the device, which are achieved by selecting high aspect ratio (A=4) and high toroidal magnetic field (16.5 T). A negative-ion-based neutral beam injection system is used both for heating and central current drive. Notable engineering features of SSTR are: the use of a uniform vacuum vessel and periodical replacements of the first wall and blanket layers and significant reduction of the electromagnetic force with the use of functionally gradient material. It is shown that a tokamak machine comparable to ITER in size can become a power reactor capable of generating about 1 GW of electricity with a plant efficiency of ∼30%. (author)
Steady states of the parametric rotator and pendulum
We discuss several steady-state rotation and oscillation modes of the planar parametric rotator and pendulum with damping. We consider a general elliptic trajectory of the suspension point for both rotator and pendulum, for the latter at an arbitrary angle with gravity, with linear and circular trajectories as particular cases. We treat the damped, nonlinear equation of motion of the parametric rotator and pendulum perturbatively for small parametric excitation and damping, although our perturbative approach can be extended to other regimes as well. Our treatment involves only ordinary second-order differential equations with constant coefficients, and provides numerically accurate perturbative solutions in terms of elementary functions. Some of the steady-state rotation and oscillation modes studied here have not been discussed in the previous literature. Other well-known ones, such as parametric resonance and the inverted pendulum, are extended to elliptic parametric excitation tilted with respect to gravity. The results presented here should be accessible to advanced undergraduates, and of interest to graduate students and specialists in the field of nonlinear mechanics.
Plasma control issues for an advanced steady state tokamak reactor
This paper deals with specific control issues related to the advanced tokamak scenarios in which rather accurate tailoring of the current density profile is a requirement in connection with the steady state operation of a reactor in a high confinement optimized shear mode. It is found that adequate current profile control can be performed if real-time magnetic flux reconstruction is available through a set of dedicated diagnostics and computers, with sufficient accuracy to deduce the radial profile of the safety factor and of the internal plasma loop voltage. It is also shown that the safety factor can be precisely controlled in the outer half of the plasma through the surface loop voltage and the off-axis current drive power, but that a compromise must be made between the accuracy of the core safety factor control and the total duration of the current and fuel density ramp-up phases, so that the demonstration of the steady state reactor potential of the optimized/reversed shear concept in the Next Step device will demand pulse lengths of the order of one thousand seconds (or more for an ITER-size machine). (author)
Nonequilibrium many-body steady states via Keldysh formalism
Maghrebi, Mohammad F.; Gorshkov, Alexey V.
2016-01-01
Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class.
Steady-state operation of spheromaks by inductive techniques
A method to maintain a steady-state spheromak configuration inductively using the S-1 Spheromak device is described. The S-1 Spheromak formation apparatus can be utilized to inject magnetic helicity continuously (C.W., not pulsed or D.C.) into the spheromak configuration after equilibrium is achieved in the linked mode of operation. Oscillation of both poloidal- and toroidal-field currents in the flux core (psi-phi Pumping), with proper phasing, injects a net time-averaged helicity into the plasma. Steady-state maintenance relies on flux conversion, which has been earlier identified. Relevant experimental data from the operation of S-1 are described. Helicity flow has been measured and the proposed injection scheme simulated. In a reasonable time practical voltages and frequencies can inject an amount of helicity comparable to that in the initial plasma. Plasma currents can be maintained or increased. This pumping technique is similar to F-THETA Pumping of a Reversed-Field-Pinch but is applied to this inverse-pinch formation
Non-steady state tidal heating of Enceladus
Shoji, D.; Hussmann, H.; Sohl, F.; Kurita, K.
2014-06-01
Enceladus is one of the most geologically active bodies in the Solar System. The satellite's diverse surface suggests that Enceladus was subject to past episodic heating. It is largely probable that the activity of Enceladus is not in a steady state. In order to analyze the non-steady state heating, thermal and orbital coupled calculation is needed because they affect each other. We perform the coupled calculation assuming conductive ice layer and low melting temperature. Although the heating state of Enceladus strongly depends on the rheological parameters used, episodic heating is induced if the Q-value of Saturn is less than 23,000 and Enceladus' core radius is less than 161 km. The duration of one episodic heating cycle is around one hundred million years. The cyclic change in ice thickness is consistent with the origin of a partial ocean which is suggested by plume emissions and diverse surface states of Enceladus. Although the obtained tidal heating rate is smaller than the observed heat flux of a few giga watt, other heating mechanisms involving e.g., liquid water and/or specific chemical reactions may be initiated by the formation of a partial or global subsurface ocean.
The relevant parameters of two steady-state models of a plasma column, in fusion regime, were analyzed for an ideal Tokamak. The neo-classical transport theory was considered in the banana regime and in the Pfirsch-Schlueter regime. The first model proposes a correction in the numerical coefficients of the transport equations. In the other one, a poloidal current from Pfirsch-Schlueter classical diffusion is considered aiming to satisfy the pressure balance. (M.C.K.)
Effect of RF field strength on steady-state NOE enhancement
The steady-state properties of a spin system irradiated by RF field are analysed. The steady-state NOE experiment is described by the extended Solomon equations. The steady-state NOE enhancement factor is obtained and verified by the experiments of liquids and solids
A mathematical model of liver metabolism: from steady state to dynamic
Calvetti, D; Kuceyeski, A [Case Western Reserve University, Department of Mathematics, 10900 Euclid Avenue, Cleveland, OH 44106 (United States); Somersalo, E [Helsinki University of Technology, Institute of Mathematics, P. O. Box 1100, FIN-02015 HUT (Finland)], E-mail: daniela.calvetti@case.edu, E-mail: amy.kuceyeski@case.edu, E-mail: erkki.somersalo@hut.fi
2008-07-15
The increase in Type 2 diabetes and other metabolic disorders has led to an intense focus on the areas of research related to metabolism. Because the liver is essential in regulating metabolite concentrations that maintain life, it is especially important to have good knowledge of the functions within this organ. In silico mathematical models that can adequately describe metabolite concentrations, flux and transport rates in the liver in vivo can be a useful predictive tool. Fully dynamic models, which contain expressions for Michaelis-Menten reaction kinetics can be utilized to investigate different metabolic states, for example exercise, fed or starved state. In this paper we describe a two compartment (blood and tissue) spatially lumped liver metabolism model. First, we use Bayesian Flux Balance Analysis (BFBA) to estimate the values of flux and transport rates at steady state, which agree closely with values from the literature. These values are then used to find a set of Michaelis-Menten parameters and initial concentrations which identify a dynamic model that can be used for exploring different metabolic states. In particular, we investigate the effect of doubling the concentration of lactate entering the system via the hepatic artery and portal vein. This change in lactate concentration forces the system to a new steady state, where glucose production is increased.
Parametric study of the primary and secondary systems of the CAREM-25 reactor on steady state
In the CAREM-25 reactor the primary coolant flows by natural convection that's why the flow is established when the balance between the buoyancy force and friction pressure drop through circuit is obtained. This paper presents a parametric study on primary and secondary systems of the reactor on steady state, for different values of some thermohydraulics parameters: safety factor on friction loss pressure calculations (f), steam generator heat transfer area (AT) and primary pressure (PP). The ESCAREM 2.08 thermohydraulic code, which calculates the primary system behavior for steady state conditions, was used for this study. The conclusions of this study are: -) There was a variation of the 15% on the primary coolant flow when the safety factor was changed a 50 %; -) The primary and secondary systems conditions do not change when the power is less than 100 MW; -) Between 100 and 110 MW the decrease of the heat transfer area produces an important change on the secondary systems conditions: the outlet steam generator temperature decrease and there is an important rice in the flow; -) The primary pressure could decrease up to 11.4 MPa without violating turbine requirements. (author)
A mathematical model of liver metabolism: from steady state to dynamic
The increase in Type 2 diabetes and other metabolic disorders has led to an intense focus on the areas of research related to metabolism. Because the liver is essential in regulating metabolite concentrations that maintain life, it is especially important to have good knowledge of the functions within this organ. In silico mathematical models that can adequately describe metabolite concentrations, flux and transport rates in the liver in vivo can be a useful predictive tool. Fully dynamic models, which contain expressions for Michaelis-Menten reaction kinetics can be utilized to investigate different metabolic states, for example exercise, fed or starved state. In this paper we describe a two compartment (blood and tissue) spatially lumped liver metabolism model. First, we use Bayesian Flux Balance Analysis (BFBA) to estimate the values of flux and transport rates at steady state, which agree closely with values from the literature. These values are then used to find a set of Michaelis-Menten parameters and initial concentrations which identify a dynamic model that can be used for exploring different metabolic states. In particular, we investigate the effect of doubling the concentration of lactate entering the system via the hepatic artery and portal vein. This change in lactate concentration forces the system to a new steady state, where glucose production is increased
ITER steady-state magnetic sensors: design status and performance
(private communication); [2] P. Moreau et al, Fusion Engineering and Design 84 (2009) 1344-1350; [3] ITER Design Description Document 55.A5,A6 Outer Vessel Steady State Sensors (private communication); [4] GRT047 Technical Report on Equilibrium reconstruction in ITER using external pick-up and steady state sensors, in preparation (private communication); [5] GRT047 Technical Report on Total toroidal current reconstruction in ITER using external pick-up and steady state sensors, in preparation (private communication). (authors)
Physics studies for steady state operation coordinated by the ITPA
Full text of publication follows. The International Tokamak Physics Activity (ITPA) aims at cooperation on an international level in development of the physics basis for burning tokamak plasmas, supporting the preparation of ITER operation, and tokamak research worldwide. The topical group on 'Integrated Operation Scenarios' coordinates research in the following 4 areas: First, IEA collaboration experiments, coordinated by the ITPA. These experiments, performed as joint experiments in several different machines, mainly concern the validation of ITER operation scenarios, including the hybrid and steady state scenarios for ITER. Specific access conditions of these two scenarios are studied together with operation close to ITER conditions. For the heating systems, specific experiments are coordinated to study the coupling of ICRH and LHCD. Secondly, modelling and benchmarking of heating systems (actuators). Benchmarking of the actuators available for heating and current drive is an important area of international collaboration. They have been performed and completed in recent years for LHCD, for ICRH and for NBCD. In particular, LHCD at high plasma density have been studied and compared to experimental data. Thirdly, the coordinated modelling of ITER scenarios. Simulations for hybrid and steady state scenarios have a particular focus on comparing code to code results (benchmarking). For hybrid scenarios the current rise phase and the current profile evolution toward q(0)=1 were modelled with various integrated modelling codes. ITER H-mode scenarios at low plasma density have been modelled showing that the burn can be sustained for > 1000 s, suitable for neutron fluence studies in ITER. The effectiveness of the ITER day-1 heating systems for obtaining steady state scenarios as well as potential heating and current drive upgrades for ITER have been evaluated. Fourth, real time control requirements. Control of burning plasma remains a focus of research
Steady-state negative Wigner functions of nonlinear nanomechanical oscillators
Rips, Simon; Wilson-Rae, Ignacio; Hartmann, Michael J
2011-01-01
We propose a scheme to prepare nanomechanical oscillators in non-classical steady states, characterized by a pronounced negative Wigner function. In our optomechanical approach, the mechanical oscillator couples to multiple laser driven resonances of an optical cavity. By lowering the resonant frequency of the oscillator via an inhomogeneous electrostatic field, we significantly enhance its intrinsic geometric nonlinearity per phonon. This causes the motional sidebands to split into separate spectral lines for each phonon number and transitions between individual phonon Fock states can be selectively addressed. We show that this enables preparation of the nanomechanical oscillator in a single phonon Fock state. Our scheme can for example be implemented with a carbon nanotube dispersively coupled to the evanescent field of a state of the art whispering gallery mode microcavity.
Steady-state negative Wigner functions of nonlinear nanomechanical oscillators
We propose a scheme for preparing nanomechanical oscillators in nonclassical steady states, characterized by a pronounced negative Wigner function. In our optomechanical approach, the mechanical oscillator couples to multiple laser-driven resonances of an optical cavity. By lowering the resonance frequency of the oscillator via an inhomogeneous electrostatic field, we significantly enhance its intrinsic geometric nonlinearity per phonon. This causes the motional sidebands to split into separate spectral lines for each phonon number and transitions between individual phonon Fock states can be selectively addressed. We show that this enables the preparation of the nanomechanical oscillator in a single-phonon Fock state. Our scheme can, for example, be implemented with a carbon nanotube dispersively coupled to the evanescent field of a state of the art whispering gallery mode microcavity. (paper)
Waveguides formed by quasi-steady-state photorefractive spatial solitons
Morin, Matthew; Duree, Galen; Salamo, Gregory; Segev, Mordechai
1995-10-01
We show that a quasi-steady-state photorefractive spatial soliton forms a waveguide structure in the bulk of a photorefractive material. Although the optically induced waveguide is formed by a very low-power (microwatts) soliton beam, it can guide a powerful (watt) beam of a longer wavelength at which the medium is nonphotosensitive. Furthermore, the waveguide survives, either in the dark or when guiding the longer-wavelength beam, for a long time after the soliton beam is turned off. We take advantage of the solitons' property of evolution from a relatively broad input beam into a narrow channel and show that the soliton induces a tapered waveguide (an optical funnel) that improves the coupling efficiency of light into the waveguiding structure.
Steady State Rheological Characteristic of Semisolid Magnesium Alloy
无
2007-01-01
Isothermal compressive experiments at different temperatures, strain rates and holding time for semisolid AZ91D, Zr modified AZ91D and MB15 alloy with higher solid volume fraction were carried out by using Gleeble-15000 simulator and the true stress-strain curves were given directly. The relationship of apparent viscosity vs temperature, shear rate and holding time of the three kinds of semi-solid magnesium alloys, as well as isothermal steady state rheological characteristic and mechanical behavior were studied. The results show that the three magnesium alloys had the characteristic of shear-thinning. The rheological characteristic of the semi-solid MB15 is different from that of semi-solid AZ91D. The semi-solid MB15 has higher apparent viscosity and deformation resistance.
NASA Lewis Steady-State Heat Pipe Code Architecture
Mi, Ye; Tower, Leonard K.
2013-01-01
NASA Glenn Research Center (GRC) has developed the LERCHP code. The PC-based LERCHP code can be used to predict the steady-state performance of heat pipes, including the determination of operating temperature and operating limits which might be encountered under specified conditions. The code contains a vapor flow algorithm which incorporates vapor compressibility and axially varying heat input. For the liquid flow in the wick, Darcy s formula is employed. Thermal boundary conditions and geometric structures can be defined through an interactive input interface. A variety of fluid and material options as well as user defined options can be chosen for the working fluid, wick, and pipe materials. This report documents the current effort at GRC to update the LERCHP code for operating in a Microsoft Windows (Microsoft Corporation) environment. A detailed analysis of the model is presented. The programming architecture for the numerical calculations is explained and flowcharts of the key subroutines are given
Steady-State Chemotactic Response in E. coli
Kafri, Yariv
2007-01-01
The bacterium E. coli maneuvers itself to regions with high chemoattractant concentrations by performing two stereotypical moves: `runs', in which it moves in near straight lines, and `tumbles', in which it does not advance but changes direction randomly. The duration of each move is stochastic and depends upon the chemoattractant concentration experienced in the recent past. We relate this stochastic behavior to the steady-state density of a bacterium population, and we derive the latter as a function of chemoattractant concentration. In contrast to earlier treatments, here we account for the effects of temporal correlations and variable tumbling durations. A range of behaviors obtains, that depends subtly upon several aspects of the system - memory, correlation, and tumbling stochasticity in particular.
Relativistic Hydrodynamics and Non-Equilibrium Steady States
Spillane, Michael
2015-01-01
We review recent interest in the relativistic Riemann problem as a method for generating a non-equilibrium steady state. In the version of the problem under con- sideration, the initial conditions consist of a planar interface between two halves of a system held at different temperatures in a hydrodynamic regime. The new double shock solutions are in contrast with older solutions that involve one shock and one rarefaction wave. We use numerical simulations to show that the older solutions are preferred. Briefly we discuss the effects of a conserved charge. Finally, we discuss deforming the relativistic equations with a nonlinear term and how that deformation affects the temperature and velocity in the region connecting the asymptotic fluids.
Factorised steady states and condensation transitions in nonequilibrium systems
M R Evans
2005-06-01
Systems driven out of equilibrium can often exhibit behaviour not seen in systems in thermal equilibrium – for example phase transitions in one-dimensional systems. In this talk I will review a simple model of a nonequilibrium system known as the `zero-range process' and its recent developments. The nonequilibrium stationary state of this model factorises and this property allows a detailed analysis of several `condensation' transitions wherein a finite fraction of the constituent particles condenses onto a single lattice site. I will then consider a more general class of mass transport models, encompassing continuous mass variables and discrete time updating, and present a necessary and sufficient condition for the steady state to factorise. The property of factorisation again allows an analysis of the condensation transitions which may occur.
Modelling of pulsed and steady-state DEMO scenarios
Giruzzi, G.; Artaud, J. F.; Baruzzo, M.; Bolzonella, T.; Fable, E.; Garzotti, L.; Ivanova-Stanik, I.; Kemp, R.; King, D. B.; Schneider, M.; Stankiewicz, R.; Stępniewski, W.; Vincenzi, P.; Ward, D.; Zagórski, R.
2015-07-01
Scenario modelling for the demonstration fusion reactor (DEMO) has been carried out using a variety of simulation codes. Two DEMO concepts have been analysed: a pulsed tokamak, characterized by rather conventional physics and technology assumptions (DEMO1) and a steady-state tokamak, with moderately advanced physics and technology assumptions (DEMO2). Sensitivity to impurity concentrations, radiation, and heat transport models has been investigated. For DEMO2, the impact of current driven non-inductively by neutral beams has been studied by full Monte Carlo simulations of the fast ion distribution. The results obtained are a part of a more extensive research and development (R&D) effort carried out in the EU in order to develop a viable option for a DEMO reactor, to be adopted after ITER for fusion energy research.
Simulation of Power Electronic Converters Using Quasi Steady State Approximation
Predrag Pejović
2012-12-01
Full Text Available A new method to compute voltage and current waveforms of power electronic converters is proposed in the paper. The method relies on simulation result of averaged circuit model, and superimposes the ripple of the inductor currents to the obtained average values, assuming that the linear ripple approximation applies. To determine the amplitude of the switching ripple, a quasi steady state approximation is proposed. After the inductor currents are obtained, currents of switching components are computed by multiplying them with appropriate switching functions. The algorithmprovides an efficient tool to generate the converter waveforms in order to compute their spectra, mean and RMS values, which are of interest in designing filters and estimating converter losses.
Steady-state, cavity-less, multimode superradiance
Greenberg, Joel A
2012-01-01
The study of collective light-matter interactions, where the dynamics of an individual scatterer depend on the state of the entire multi-scatterer system, has recently received much attention in the areas of fundamental research and photonic technologies. Cold atomic vapors represent an exciting system for studying such effects because light-based manipulation of internal and center-of-mass atomic states lead to reduced instability thresholds and new phonomena. Previous investigations required single-mode cavities to realize strong light mediated atom-atom interactions, though, which limits the observable phenomena. Here we demonstrate steady-state, mirrorless superradiance in a cold vapor pumped by weak optical fields. Beyond a critical pumping strength, the vapor spontaneously transforms into a spatially self-organized state: a density grating forms. Scattering of the pump beams off this grating generates new optical fields that act back on the vapor to enhance the atomic organization. This system has appli...
The thermal vacuum for non-equilibrium steady state
Imai, Ryosuke; Kuwahara, Yukiro; Nakamura, Yusuke; Yamanaka, Yoshiya
Our purpose is to construct a theoretical description of non-equilibrium steady state (NESS), employing thermo field dynamics (TFD). TFD is the operator-based formalism of thermal quautum field theory, where every degree of freedom is doubled and thermal averages are given by expectation values of the thermal vacuum. To specify the thermal vacuum for NESS is a non-trivial issue, and we attempt it on the analogy between the superoperator formalism and TFD. Using the thermal vacuum thus obtained, we analyze the NESS which is realized in the two-reservoir model. It will be shown that the NESS vacuum of the model coincides with the fixed point solutions of the quantum transport equation derived by the self-consistent renormalization of the self-energy in non-equilibrium TFD.
Avoiding Rebound through a Steady-State Economy
Nørgaard, Jørgen
2008-01-01
The debate on the rebound effect as presented in most chapters in this book is based upon experience from the past more than visions of the future. The analyses are dominated by conventional economic theory, which implicitly assumes insatiable demand for energy services. Material consumption is...... only buy some time. From this perspective, the environmental problem with the rebound effect is not the higher energy efficiency, which pushes towards lower flows of resources through the economy, but rather the conventional economy which rebounds the savings, because of its quest for higher flows. In...... this chapter, I shall take the rebound debate further by discussing the possible role of energy efficiency in a sustainable economy that is based on the notion of ‘sufficiency’. The assumption is that globally we need to achieve a ‘steady-state economy’. Considering the urgent need for better material...
Stationary Distribution and Thermodynamic Relation in Nonequilibrium Steady States
Komatsu, Teruhisa S.
2010-01-01
We describe our recent attempts toward statistical mechanics and thermodynamics for nonequilibrium steady states (NESS) realized, e.g., in a heat conducting system. Our first result is a simple expression of the probability distribution (of microscopic states) of a NESS. Our second result is a natural extension of the thermodynamic Clausius relation and a definition of an accompanying entropy in NESS. This entropy coincides with the normalization constant appearing in the above mentioned microscopic expression of NESS, and has an expression similar to the Shannon entropy (with a further symmetrization). The NESS entropy proposed here is a clearly defined measurable quantity even in a system with a large degrees of freedom. We numerically measure the NESS entropy in hardsphere fluid systems with a heat current, by observing energy exchange between the system and the heat baths when the temperatures of the baths are changed according to specified protocols.
Stabilization of unstable steady states by variable delay feedback control
Gjurchinovski, Aleksandar
2008-01-01
We report on a dramatic improvement of the performance of the classical time-delayed autosynchronization method (TDAS) to control unstable steady states, by applying a time-varying delay in the TDAS control scheme in a form of a deterministic or stochastic delay-modulation in a fixed interval around a nominal value $T_0$. The successfulness of this variable delay feedback control (VDFC) is illustrated by a numerical control simulation of the Lorenz and R\\"{o}ssler systems using three different types of time-delay modulations: a sawtooth wave, a sine wave, and a uniform random distribution. We perform a comparative analysis between the VDFC method and the standard TDAS method for a sawtooth-wave modulation by analytically determining the domains of control for the generic case of an unstable fixed point of focus type.
Transient and steady state modelling of a coupled WECS
Nathan, G. K.; Tan, J. K.
The paper presents a method for simulation of a wind turbine using a dc motor. The armature and field voltages of the dc motor are independently regulated to obtain torque-speed characteristics which correspond to those of a wind turbine at different wind speeds. The mass moment of inertia of the wind turbine is represented by adding a rotating mass to a parallel shaft which is positively coupled to the motor shaft. To verify the method of simulation, an American multiblade wind turbine is chosen, loaded by coupling to a centrifugal pump. Using the principle of conservation of energy and characteristics of both constituent units, two mathematical models are proposed: one for steady state operation and another for the transient state. The close comparison between the theoretical and the experimental results validates the proposed models and the method of simulation. The experimental method is described and the results of the experimental and theoretical investigation are presented.
Steady States in SIRS Epidemical Model of Mobile Individuals
Zhang, Duan-Ming; He, Min-Hua; Yu, Xiao-Ling; Pan, Gui-Jun; Sun, Hong-Zhang; Su, Xiang-Ying; Sun, Fan; Yin, Yan-Ping; Li, Rui; Liu, Dan
2006-01-01
We consider an epidemical model within socially interacting mobile individuals to study the behaviors of steady states of epidemic propagation in 2D networks. Using mean-field approximation and large scale simulations, we recover the usual epidemic behavior with critical thresholds δc and pc below which infectious disease dies out. For the population density δ far above δc, it is found that there is linear relationship between contact rate λ and the population density δ in the main. At the same time, the result obtained from mean-field approximation is compared with our numerical result, and it is found that these two results are similar by and large but not completely the same.
Charged particle creation in the steady state universe
The birth of a particle of charge q(0), initial mass m(0), and radius a in the steady state universe is studied. With the particle's birth, in accord with causality, gravity, and Coulomb fields propagate away from it with the speed of light. Field energies are supplied by the particle's mass which subsequently decays in time. Asymptotic solution to a nonlinear equation for the remaining mass gives the criterion m(0) is greater that q(0)2/2ac2 as a necessary condition for the initial mass to survive the field expansion. The resulting radius of a classical charged particle is found to be greater than the standard value obtained by equating self- and rest-mass energies of the initial particle. 12 refs
Steady-state solution methods for open quantum optical systems
Nation, P D
2015-01-01
We discuss the numerical solution methods available when solving for the steady-state density matrix of a time-independent open quantum optical system, where the system operators are expressed in a suitable basis representation as sparse matrices. In particular, we focus on the difficulties posed by the non-Hermitian structure of the Lindblad super operator, and the numerical techniques designed to mitigate these pitfalls. In addition, we introduce a doubly iterative inverse-power method that can give reduced memory and runtime requirements in situations where other iterative methods are limited due to poor bandwidth and profile reduction. The relevant methods are demonstrated on several prototypical quantum optical systems where it is found that iterative methods based on iLU factorization using reverse Cuthill-Mckee ordering tend to outperform other solution techniques in terms of both memory consumption and runtime as the size of the underlying Hilbert space increases. For eigenvalue solving, Krylov iterat...
An Adsorption Equilibria Model for Steady State Analysis
Ismail, Azhar Bin
2016-02-29
The investigation of adsorption isotherms is a prime factor in the ongoing development of adsorption cycles for a spectrum of advanced, thermally-driven engineering applications, including refrigeration, natural gas storage, and desalination processes. In this work, a novel semi-empirical mathematical model has been derived that significantly enhances the prediction of the steady state uptake in adsorbent surfaces. This model, a combination of classical Langmuir and a novel modern adsorption isotherm equation, allows for a higher degree of regression of both energetically homogenous and heterogeneous adsorbent surfaces compared to several isolated classical and modern isotherm models, and has the ability to regress isotherms for all six types under the IUPAC classification. Using a unified thermodynamic framework, a single asymmetrical energy distribution function (EDF) has also been proposed that directly relates the mathematical model to the adsorption isotherm types. This fits well with the statistical rate theory approach and offers mechanistic insights into adsorption isotherms.
Entanglement structure of non-equilibrium steady states
Mahajan, Raghu; Mumford, Sam; Tubman, Norm; Swingle, Brian
2016-01-01
We study the problem of calculating transport properties of interacting quantum systems, specifically electrical and thermal conductivities, by computing the non-equilibrium steady state (NESS) of the system biased by contacts. Our approach is based on the structure of entanglement in the NESS. With reasonable physical assumptions, we show that a NESS close to local equilibrium is lightly entangled and can be represented via a computationally efficient tensor network. We further argue that the NESS may be found by dynamically evolving the system within a manifold of appropriate low entanglement states. A physically realistic law of dynamical evolution is Markovian open system dynamics, or the Lindblad equation. We explore this approach in a well-studied free fermion model where comparisons with the literature are possible. We study both electrical and thermal currents with and without disorder, and compute entropic quantities such as mutual information and conditional mutual information. We conclude with a di...
Fast Prediction Method for Steady-State Heat Convection
Wáng, Yì
2012-03-14
A reduced model by proper orthogonal decomposition (POD) and Galerkin projection methods for steady-state heat convection is established on a nonuniform grid. It was verified by thousands of examples that the results are in good agreement with the results obtained from the finite volume method. This model can also predict the cases where model parameters far exceed the sample scope. Moreover, the calculation time needed by the model is much shorter than that needed for the finite volume method. Thus, the nonuniform POD-Galerkin projection method exhibits high accuracy, good suitability, and fast computation. It has universal significance for accurate and fast prediction. Also, the methodology can be applied to more complex modeling in chemical engineering and technology, such as reaction and turbulence. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Steady state asymmetric planetary electrical induction. [by solar wind
Horning, B. L.; Schubert, G.
1974-01-01
An analytic solution is presented for the steady state electric and magnetic fields induced by the motional electric field of the solar wind in the atmosphere or interior of a planet that is asymmetrically surrounded by solar wind plasma. The electrically conducting ionosphere or interior must be in direct electrical contact with the solar wind over the day side of the planet. The conducting region of the planet is modeled by a sphere or a spherical shell of arbitrarily stratified electrical conductivity. A monoconducting cylindrical cavity is assumed to extend downstream on the night side of the planet. The solar wind is assumed to be highly conducting so that the induced fields are confined to the planet and cavity. Induced currents close as sheet currents at the solar wind-cavity and solar wind-planet interfaces. Numerical evaluations of the analytic formulas are carried out for a uniformly conducting spherical model.
Preliminary design study of a steady state tokamak device
Preliminary design study has been made for a steady tokamak with the plasma current of 10MA, as the next to the JT-60U experimental programs. The goal of the research program is the integrated study of steady state, high-power physics and technology. Present candidate design is to use superconducting TF and PF magnet systems and long pulse operation of 100's-1000's of sec with non inductive current drive mainly by 500keV negative ion beam injection of 60MW. Low activation material such as titanium alloy is chosen for the water tank type vacuum vessel, which is also the nuclear shield for the superconducting coils. The present preliminary design study shows that the device can meet the existing JT-60U facility capability. (author)
Determining "small parameters" for quasi-steady state
Goeke, Alexandra; Walcher, Sebastian; Zerz, Eva
2015-08-01
For a parameter-dependent system of ordinary differential equations we present a systematic approach to the determination of parameter values near which singular perturbation scenarios (in the sense of Tikhonov and Fenichel) arise. We call these special values Tikhonov-Fenichel parameter values. The principal application we intend is to equations that describe chemical reactions, in the context of quasi-steady state (or partial equilibrium) settings. Such equations have rational (or even polynomial) right-hand side. We determine the structure of the set of Tikhonov-Fenichel parameter values as a semi-algebraic set, and present an algorithmic approach to their explicit determination, using Groebner bases. Examples and applications (which include the irreversible and reversible Michaelis-Menten systems) illustrate that the approach is rather easy to implement.
Laguna Verde BWRs operational experience: steady-state fuel performance
The two BWR at Laguna Verde nuclear power station are finishing 21 and 15 years of continuous successful operation as of 2010. During Unit 1 and 2 commercial operations only Ge/GNF fuel designs have been employed; fuel lattice designs 8 x 8 and 10 x 10 were used at the reactor, with an original licensed thermal power (OLTP: 1931 MWt) and the reactor's first power up-rates of 5%. GNF fuel will be also used for the second EPU to reach 120% of OLTP in the near future. Thermal and gamma traversing in-core probes (Tip) are used for power monitoring purposes along with the Ge (now GNF-A) core monitoring system, 3-dimensional MonicoreTM. GNF-A has also participated by preparing the core management plan that is regularly fine-tuned in collaboration with Comision Federal de Electricidad (CFE owner of the Laguna Verde reactors). For determination of thermal margins and eigenvalue prediction, GNF-A employs the NRC-licensed steady-state core simulator PANAC11. Tip comparisons are routinely used to adapt power distributions for a better thermal margin calculation. Over the years, several challenges have appeared in the near and long term fuel management planning such as increasing cycle length, optimization of the thermal margins, rated power increase, etc. Each challenge has been successfully overcome via operational strategy, code improvements and better fuel designs. This paper summarizes Laguna Verde Unit 1 and 2 steady-state performance from initial commercial operation, with a discussion of the nuclear and thermal-hydraulic design features, as well as of the operational strategies that set and interesting benchmark for future fuel applications, code development and operation of the BWRs. (Author)
Steady-state spectroscopy of new biological probes
Abou-Zied, Osama K.
2007-02-01
The steady state absorption and fluorescence spectroscopy of 2-(2'-hydroxyphenyl)benzoxazole (HBO) and (2,2'-bipyridine)-3,3'-diol (BP(OH) II) were studied here free in solution and in human serum albumin (HSA) in order to test their applicability as new biological probes. HBO and BP(OH) II are known to undergo intramolecular proton transfers in the excited state. Their absorption and fluorescence spectra are sensitive to environmental change from hydrophilic to hydrophobic, thus allowing the opportunity to use them as environment-sensitive probes. The effect of water on the steady state spectra of the two molecules also shows unique features which may position them as water sensors in biological systems. For HBO in buffer, fluorescence is only due to the syn-keto tautomer, whereas in HSA the fluorescence is due to four species in equilibrium in the excited state (the syn-keto tautomer, the anti-enol tautomer, the solvated syn-enol tautomer, and the anion species of HBO). Analysis of the fluorescence spectra of HBO in HSA indicates that HBO is exposed to less water in the HBO:HSA complex. For the BP(OH) II molecule, unique absorption due to water was observed in the spectral region of 400-450 nm. This absorption decreases in the presence of HSA due to less accessibility to water as a result of binding to HSA. Fluorescence of BP(OH) II is due solely to the di-keto tautomer after double proton transfer in the excited state. The fluorescence peak of BP(OH) II shows a red-shift upon HSA recognition which is attributed to the hydrophobic environment inside the binding site of HSA. We discuss also the effect of probe-inclusion inside well-defined hydrophobic cavities of cyclodextrins.
Steady state plasma operation in RF dominated regimes on EAST
Zhang, X. J.; Zhao, Y. P.; Gong, X. Z.; Hu, C. D.; Liu, F. K.; Hu, L. Q.; Wan, B. N., E-mail: bnwan@ipp.ac.cn; Li, J. G. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2015-12-10
Significant progress has recently been made on EAST in the 2014 campaign, including the enhanced CW H&CD system over 20MW heating power (LHCD, ICRH and NBI), more than 70 diagnostics, ITER-like W-monoblock on upper divertor, two inner cryo-pumps and RMP coils, enabling EAST to investigate long pulse H mode operation with dominant electron heating and low torque to address the critical issues for ITER. H-mode plasmas were achieved by new H&CD system or 4.6GHz LHCD alone for the first time. Long pulse high performance H mode has been obtained by LHCD alone up to 28s at H{sub 98}∼1.2 or by combing of ICRH and LHCD, no or small ELM was found in RF plasmas, which is essential for steady state operation in the future Tokamak. Plasma operation in low collision regimes were implemented by new 4.6GHz LHCD with core Te∼4.5keV. The non-inductive scenarios with high performance at high bootstrap current fraction have been demonstrated in RF dominated regimes for long pulse operation. Near full non-inductive CD discharges have been achieved. In addition, effective heating and decoupling method under multi-transmitter for ICRF system were developed in this campaign, etc. EAST could be in operation with over 30MW CW heating and current drive power (LHCD ICRH NBI and ECRH), enhanced diagnostic capabilities and full actively-cooled metal wall from 2015. It will therefore allow to access new confinement regimes and to extend these regimes towards to steady state operation.
Thermodynamic Study of a Low Temperature Difference Stirling Engine at Steady State Operation
Pierre Rochelle
2007-12-01
Full Text Available In the current energy economy context, the use of renewable energies and the valuation of lost energies are the subject of many studies. From this point of view, the Stirling engine draws attention of the researchers for its many advantages. This paper presents a thermodynamic analysis of a low temperature Stirling engine at steady state operation; energy, entropy and exergy balances being presented at each main element of the engine. A zero dimensional numerical model describing the variables evolution (pressure, volumes, masses, exchanged energies, irreversibilities... as function of the crankshaft angle is also presented. The calculated irreversibilities are due to imperfect regeneration and temperature differences between gas and wall in the hot and cold exchangers. A favourable comparison was made with experimental results obtained on an small size engine.
Phase-sensitive fat suppression steady-state free procession sequence with phase correction
Zu Zhong-Liang; Zhou Kun; Zhang Shi-Gang; Gao Song; Bao Shang-Lian
2008-01-01
Robust and fast fat suppression is a challenge in balanced steady-state free precession (SSFP) magnetic resonance imaging.Although single-acquisition phase-sensitive SSFP can provide fat-suppressed images in short scan time,phase errors,especially spatially-dependent phase shift,caused by a variety of factors may result in misplacement of fat and water voxels.In this paper,a novel phase correction algorithm was used to calibrate those phase errors during image reconstruction.This algorithm corrects phase by region growing,employing both the magnitude and the phase information of image pixels.Phantom and in vivo imagings were performed to validate the technique.As a result,excellent fat-suppressed images were acquired by using single-acquisition phase-seusitive SSFP with phase correction.
In a sugar refinery, the juice is concentrated through evaporation, with the objective of concentrating the juice to syrup as rapidly as possible. Because the heat of vaporization of water is relatively high, the evaporation process can be highly energy intensive, and therefore the economical use of steam is important in the refinery. This paper reports on the development of a simulation model for the evaporation sections of two Mauritian sugar refineries. The first objective was to use the simulation model to carry out an energy balance over the evaporators in order to assess the economy of steam usage over the refinery. The second objective was to examine to what extent a fundamental steady state model, based on thermodynamics (not kinetics) was capable of predicting the material and energy flows in two operating sugar refineries and thereby to evaluate the applicability of the modelling framework. The simulation model was validated using historical data as well as data from the plant DCS system. The simulation results generally correlated well with the measured values, except for one of the evaporators on one refinery. Some suggestions were made as to the cause of the discrepancy. On balance, it was found that both refineries are extremely efficient in terms of steam and equipment usage and that there is not much scope for energy optimisation within the present configuration - nor for much spare steam capacity for an additional refinery. It was also shown that steady state process simulation, using thermodynamic models, can generate a very useful representation of a working refinery. Besides being able to use the model to 'benchmark' the operation and thus evaluate its performance as a whole as well as across individual units, it could also be used to evaluate refinery performance across refineries, nationally as well as globally.
Steady-state compact neutron sources with HTS magnets
Full text of publication follows. Recent advantages in the development of high temperature superconductors (HTS), and encouraging results of first tests of HTS coils on a tokamak [1], open new prospects for compact high field TF magnets for Spherical Tokamaks (STs). High β (ratio of the plasma pressure to magnetic pressure) values have been achieved in STs, which opens a path to compact Fusion devices, as the Fusion power is proportional to β2Bt4V. To make advantages of high β in compact STs, the toroidal field should be maximised, which is challenging, and all present STs operate at fields < 1 T. The favourable dependence of confinement on Bt recently found in STs [2] may allow enhanced performance in high-field STs, also encouraging increase in Bt. We investigate feasibility of HTS magnets in next-step STs and compare such designs with proposed conventional aspect ratio designs with HTS magnets (VECTOR, VULCAN etc). Main issues are: - the capital cost (will the use of HTS increase the capital cost?); - running cost (can the use of HTS reduce the running cost?); - will increase in the field in STs easy requirements on current drive?; - how much use of HTS will affect the size (e.g. the cost) of a neutron source (divertor, blanket maintenance options, shielding etc.)? Several physics aspects of a low- and medium-power steady-state neutron source will be discussed. These include fast particle and alpha particle losses, effect of increase in Bt on micro-stability etc. The demonstration of reliable steady state operations in a compact ST even at the level of a few MW Fusion output (which easy application of HTS) as a first step will significantly advance not only the mainstream Fusion for Energy research, but also the commercial exploitation of Fusion Power. [1] M Gryaznevich et al., 'Progress in applications of High Temperature Superconductor in Tokamak Magnets', Fusion Engineering and Design, accepted for publication, (2013). [2] M. Valovic et al, Nucl
A simplified system for steady state process simulation
The system described in this report represents an attempt to apply the function of industrial flow sheet simulators to tritium processing applications. To overcome some of the difficulties associated with the use of larger simulation packages, report formats have been designed to accommodate wide ranges of component concentrations; and physical property data requirements have been designed around commonly available data. The simulation system includes a predefined structure for storage of stream and component data, unit operation block parameters, and the other data needed to describe a simulation. Other support subroutines, which are needed to perform computations common to different unit operation subroutines, are included, along with some of the more common unit operation modules. To perform a simulation, the user codes an executive routine that calls the appropriate support and unit operation subroutines - as well as any additional support or unit operation subroutines not already part of the system. This code is then compiled and linked to a library, which contains the existent parts of the system, to produce an executable program. This program is run, with the user's data file as input, to compute the steady state performance of the flow sheet being simulated. The existent part of the system is coded in Microsoft FORTRAN-77, which should be largely compatible with other FORTRAN compilers. The simulation system has been compiled and placed in a library which is usable by a Microsoft linkage editor on an IBM PC
Steady state relativistic stellar dynamics around a massive black hole
Bar-Or, Ben
2015-01-01
A massive black hole (MBH) consumes stars whose orbits evolve into the small phase-space volume of unstable orbits, the "loss-cone", which take them directly into the MBH, or close enough to interact strongly with it. The resulting phenomena: tidal heating and tidal disruption, binary capture and hyper-velocity star ejection, gravitational wave (GW) emission by inspiraling compact remnants, or hydrodynamical interactions with an accretion disk, are of interest as they can produce observable signatures and thereby reveal the existence of the MBH, affect its mass and spin evolution, probe strong gravity, and provide information on stars and gas near the MBH. The continuous loss of stars and the processes that resupply them shape the central stellar distribution. We investigate relativistic stellar dynamics near the loss-cone of a non-spinning MBH in steady-state analytically and by Monte Carlo simulations of the diffusion of the orbital parameters. These take into account Newtonian mass precession due to enclos...
Comparison of Gene Regulatory Networks via Steady-State Trajectories
Seungchan Kim
2007-05-01
Full Text Available The modeling of genetic regulatory networks is becoming increasingly widespread in the study of biological systems. In the abstract, one would prefer quantitatively comprehensive models, such as a differential-equation model, to coarse models; however, in practice, detailed models require more accurate measurements for inference and more computational power to analyze than coarse-scale models. It is crucial to address the issue of model complexity in the framework of a basic scientific paradigm: the model should be of minimal complexity to provide the necessary predictive power. Addressing this issue requires a metric by which to compare networks. This paper proposes the use of a classical measure of difference between amplitude distributions for periodic signals to compare two networks according to the differences of their trajectories in the steady state. The metric is applicable to networks with both continuous and discrete values for both time and state, and it possesses the critical property that it allows the comparison of networks of different natures. We demonstrate application of the metric by comparing a continuous-valued reference network against simplified versions obtained via quantization.
Comparison of Gene Regulatory Networks via Steady-State Trajectories
Choi Woonjung
2007-01-01
Full Text Available The modeling of genetic regulatory networks is becoming increasingly widespread in the study of biological systems. In the abstract, one would prefer quantitatively comprehensive models, such as a differential-equation model, to coarse models; however, in practice, detailed models require more accurate measurements for inference and more computational power to analyze than coarse-scale models. It is crucial to address the issue of model complexity in the framework of a basic scientific paradigm: the model should be of minimal complexity to provide the necessary predictive power. Addressing this issue requires a metric by which to compare networks. This paper proposes the use of a classical measure of difference between amplitude distributions for periodic signals to compare two networks according to the differences of their trajectories in the steady state. The metric is applicable to networks with both continuous and discrete values for both time and state, and it possesses the critical property that it allows the comparison of networks of different natures. We demonstrate application of the metric by comparing a continuous-valued reference network against simplified versions obtained via quantization.
Steady-state growth of the marine diatom Thalassiosira pseudonana
Olson, R.J. (Scripps Inst. of Oceanography, La Jolla, CA); SooHoo, J.B.; Kiefer, D.A.
1980-09-01
Seasonal studies of the vertical distribution of nitrate, nitrite, and phytoplankton in the oceans and studies using /sup 15/N as a tracer of nitrate metabolism indicate that the reduction of nitrate by phytoplankton is a source of nitrite in the upper waters of the ocean. To better understand this process, the relationship between nitrate uptake and nitrite production has been examined with continuous cultures of the small marine diatom Thalassiosira pseudonana. In a turbidostat culture, the rates of nitrite production by T. Pseudonana increase with light intensity. This process is only loosely coupled to rates of nitrate assimilation since the ratio of net nitrite production to total nitrate assimilation increases with increased rates of growth. In continuous cultures where steady-state concentrations of nitrate and nitrite were varied, T. pseudonana produced nitrite at rates which increased with increasing concentrations of nitrate. Again, the rates of nitrite production were uncoupled from rates of nitrate assimilation. The study was used to derive a mathematical description of nitrate and nitrite metabolism by T. pseudonana. The validity of this model was supported by the results of a study in which /sup 15/N-labeled nitrite was introduced into the continuous culture, and the model was used to examine patterns in distribution of nitrite in the Antarctic Ocean and the Sargasso Sea.
Steady-state growth of the marine diatom Thalassiosira pseudonana
Seasonal studies of the vertical distribution of nitrate, nitrite, and phytoplankton in the oceans and studies using 15N as a tracer of nitrate metabolism indicate that the reduction of nitrate by phytoplankton is a source of nitrite in the upper waters of the ocean. To better understand this process, the relationship between nitrate uptake and nitrite production has been examined with continuous cultures of the small marine diatom Thalassiosira pseudonana. In a turbidostat culture, the rates of nitrite production by T. Pseudonana increase with light intensity. This process is only loosely coupled to rates of nitrate assimilation since the ratio of net nitrite production to total nitrate assimilation increases with increased rates of growth. In continuous cultures where steady-state concentrations of nitrate and nitrite were varied, T. pseudonana produced nitrite at rates which increased with increasing concentrations of nitrate. Again, the rates of nitrite production were uncoupled from rates of nitrate assimilation. The study was used to derive a mathematical description of nitrate and nitrite metabolism by T. pseudonana. The validity of this model was supported by the results of a study in which 15N-labeled nitrite was introduced into the continuous culture, and the model was used to examine patterns in distribution of nitrite in the Antarctic Ocean and the Sargasso Sea
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases.
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state. PMID:26764644
Development of the ITER Advanced Steady State and Hybrid Scenarios
Full discharge simulations are performed to examine the plasma current rampup, flattop and rampdown phases self-consistently with the poloidal field (PF) coils and their limitations, plasma transport evolution, and heating/current drive (H/CD) sources. Steady state scenarios are found that obtain 100% non-inductive current with Ip = 7.3-10.0 MA, ΒN ∼ 2.5 for H98 = 1.6, Q's range from 3 to 6, n/nGr = 0.75-1.0, and NB, IC, EC, and LH source have been examined. The scenarios remain within CS/PF coil limits by advancing the pre-magnetization by 40 Wb. Hybrid scenarios have been identified with 35-40% non-inductive current for Ip = 12.5 MA, H98 ∼ 1.25, with q(0) reaching 1 at or after the end of rampup. The equilibrium operating space for the hybrid shows a large range of scenarios can be accommodated, and access 925-1300 s flattop burn durations.
Flavour fields in steady state: stress tensor and free energy
Banerjee, Avik; Kundu, Arnab; Kundu, Sandipan
2016-02-01
The dynamics of a probe brane in a given gravitational background is governed by the Dirac-Born-Infeld action. The corresponding open string metric arises naturally in studying the fluctuations on the probe. In Gauge-String duality, it is known that in the presence of a constant electric field on the worldvolume of the probe, the open string metric acquires an event horizon and therefore the fluctuation modes on the probe experience an effective temperature. In this article, we bring together various properties of such a system to a formal definition and a subsequent narration of the effective thermodynamics and the stress tensor of the corresponding flavour fields, also including a non-vanishing chemical potential. In doing so, we point out a potentially infinitely-degenerate scheme-dependence of regularizing the free energy, which nevertheless yields a universal contribution in certain cases. This universal piece appears as the coefficient of a log-divergence in free energy when a space-filling probe brane is embedded in AdS d+1-background, for d = 2, 4, and is related to conformal anomaly. For the special case of d = 2, the universal factor has a striking resemblance to the well-known heat current formula in (1 + 1)-dimensional conformal field theory in steady-state, which endows a plausible physical interpretation to it. Interestingly, we observe a vanishing conformal anomaly in d = 6.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.
Estimation of the Maximal Lactate Steady State in Endurance Runners.
Llodio, I; Gorostiaga, E M; Garcia-Tabar, I; Granados, C; Sánchez-Medina, L
2016-06-01
This study aimed to predict the velocity corresponding to the maximal lactate steady state (MLSSV) from non-invasive variables obtained during a maximal multistage running field test (modified University of Montreal Track Test, UMTT), and to determine whether a single constant velocity test (CVT), performed several days after the UMTT, could estimate the MLSSV. Within 4-5 weeks, 20 male runners performed: 1) a modified UMTT, and 2) several 30 min CVTs to determine MLSSV to a precision of 0.25 km·h(-1). Maximal aerobic velocity (MAV) was the best predictor of MLSSV. A regression equation was obtained: MLSSV=1.425+(0.756·MAV); R(2)=0.63. Running velocity during the CVT (VCVT) and blood lactate at 6 (La6) and 30 (La30) min further improved the MLSSV prediction: MLSSV=VCVT+0.503 - (0.266·ΔLa30-6); R(2)=0.66. MLSSV can be estimated from MAV during a single maximal multistage running field test among a homogeneous group of trained runners. This estimation can be further improved by performing an additional CVT. In terms of accuracy, simplicity and cost-effectiveness, the reported regression equations can be used for the assessment and training prescription of endurance runners. PMID:27116348
Hyperbolic method for magnetic reconnection process in steady state magnetohydrodynamics
Baty, Hubert; Nishikawa, Hiroaki
2016-06-01
A recent numerical approach for solving the advection-diffusion and Navier-Stokes equations is extended for the first time to a magnetohydrodynamic (MHD) model, aiming in particular consistent improvements over classical methods for investigating the magnetic reconnection process. In this study, we mainly focus on a two-dimensional incompressible set of resistive MHD equations written in flux-vorticity scalar variables. The originality of the method is based on hyperbolic reformulation of the dissipative terms, leading to the construction of an equivalent hyperbolic first-order (spatial derivatives) system. This enables the use of approximate Riemann solvers for handling dissipative and advective flux in the same way. A simple second-order finite-volume discretization on rectangular grids using an upwind flux is employed. The advantages of this method are illustrated by a comparison to two particular analytical steady state solutions of the inviscid magnetic reconnection mechanism, namely the magnetic annihilation and the reconnective diffusion problems. In particular, the numerical solution is obtained with the same order of accuracy for the solution and gradient for a wide range of magnetic Reynolds numbers, without any deterioration characteristic of more conventional schemes. The amelioration of the hyperbolic method and its extension to time-dependent MHD problems related to solar flares mechanisms is also discussed.
The Path of Carbon in Photosynthesis. XX. The Steady State
Calvin, M.; Massini, Peter
1952-09-01
The separation of the phenomenon of photosynthesis in green plants into a photochemical reaction and into the light-dependent reduction of carbon dioxide is discussed, The reduction of carbon dioxide and the fate of the assimilated carbon were investigated with the help of the tracer technique (exposure of the planks to the radioactive C{sup 14}O{sub 2}) and of paper chromatography. A reaction cycle is proposed in which phosphoglyceric acid is the first isolable assimilations product. Analyses of the algal extracts which had assimilated radioactive carbon dioxide in a stationary condition ('steady-state' photosynthesis) for a long time provided further information concerning the proposed cycle and permitted the approximate estimation, for a number of compounds of what fraction of each compound was taking part in the cycle. The earlier supposition that light influences the respiration cycle was confirmed. The possibility of the assistance of {alpha}-lipoic acid, or of a related substance, in this influence and in the photosynthesis cycle, is discussed.
Interplanetary cosmic ray radial gradients with steady state modulation models
Potgieter, M.S.; Le Roux, J.A.; Burger, R.A.
1989-03-01
We have used steady state modulation models of increasing complexity, with emphasis on drift models, to establish to what extent these models can simulate the observed cosmic ray integral radial gradient (energygreater than or equal to60--70 MeV/nucleon) in the heliosphere from 1977 to 1986. Special attention has been given to the apparent asymmetric behavior of the radial gradient with respect to the recent interplanetary magnetic field polarity reversal, and the remarkable constant radial gradient for the years 1977--1982. Instead of using differential intensities at specific energies, we presented integral radial gradients calculated from the computed integral intensities which made comparison with observations more realistic. We found that nondrift models had difficulties producing constant radial gradients over several years of increasing solar activity, because these models depend primarily on changes of the radial diffusion coefficient K/sub r//sub r/ to simulate an 11-year cycle and therefore produce, in general, radial gradients symmetric with respect to solar maximum activity. Making these models independent of changes in K/sub r//sub r/ needs, in our opinion, unrealistic changes in the conventional modulation parameters.
Kinematical Analysis along Maximal Lactate Steady State Swimming Intensity
Pedro Figueiredo, Rafael Nazario, Marisa Sousa, Jailton Gregório Pelarigo, João Paulo Vilas-Boas, Ricardo Fernandes
2014-09-01
Full Text Available The purpose of this study was to conduct a kinematical analysis during swimming at the intensity corresponding to maximal lactate steady state (MLSS. Thirteen long distance swimmers performed, in different days, an intermittent incremental protocol of n x 200 m until exhaustion and two to four 30-min submaximal constant speed bouts to determine the MLSS. The video analysis, using APAS System (Ariel Dynamics Inc., USA, allowed determining the following relevant swimming determinants (in five moments of the 30-min test: 0, 25, 50, 75, and 100%: stroke rate, stroke length, trunk incline, intracyclic velocity variation, propelling efficiency, index of coordination and the time allotted to propulsion per distance unit. An ANOVA for repeated measures was used to compare the parameters mean values along each moment of analysis. Stoke rate tended to increase and stroke length to decrease along the test; a tendency to decrease was also found for intracyclic velocity variation and propelling efficiency whereas the index of coordination and the propulsive impulse remained stable during the MLSS test. It can be concluded that the MLSS is not only an intensity to maintain without a significant increase of blood lactate concentration, but a concomitant stability for some biomechanical parameters exists (after an initial adaptation. However, efficiency indicators seem to be more sensitive to changes occurring during swimming at this threshold intensity.
Dynamic steady-state of periodically-driven quantum systems
Yudin, V I; Basalaev, M Yu; Kovalenko, D
2015-01-01
Using the density matrix formalism, we prove an existence theorem of the periodic steady-state for an arbitrary periodically-driven system. This state has the same period as the modulated external influence, and it is realized as an asymptotic solution ($t$$\\to$$+\\infty$) due to relaxation processes. The presented derivation simultaneously contains a simple computational algorithm non-using both Floquet and Fourier theories, i.e. our method automatically guarantees a full account of all frequency components. The description is accompanied by the examples demonstrating a simplicity and high efficiency of our method. In particular, for three-level $\\Lambda$-system we calculate the lineshape and field-induced shift of the dark resonance formed by the field with periodically modulated phase. For two-level atom we obtain the analytical expressions for signal of the direct frequency comb spectroscopy with rectangular light pulses. In this case it was shown the radical dependence of the spectroscopy lineshape on pul...
Progress Toward Steady State Tokamak Operation Exploiting the high bootstrap current fraction regime
Ren, Q.
2015-11-01
Recent DIII-D experiments have advanced the normalized fusion performance of the high bootstrap current fraction tokamak regime toward reactor-relevant steady state operation. The experiments, conducted by a joint team of researchers from the DIII-D and EAST tokamaks, developed a fully noninductive scenario that could be extended on EAST to a demonstration of long pulse steady-state tokamak operation. Fully noninductive plasmas with extremely high values of the poloidal beta, βp >= 4 , have been sustained at βT >= 2 % for long durations with excellent energy confinement quality (H98y,2 >= 1 . 5) and internal transport barriers (ITBs) generated at large minor radius (>= 0 . 6) in all channels (Te, Ti, ne, VTf). Large bootstrap fraction (fBS ~ 80 %) has been obtained with high βp. ITBs have been shown to be compatible with steady state operation. Because of the unusually large ITB radius, normalized pressure is not limited to low βN values by internal ITB-driven modes. βN up to ~4.3 has been obtained by optimizing the plasma-wall distance. The scenario is robust against several variations, including replacing some on-axis with off-axis neutral beam injection (NBI), adding electron cyclotron (EC) heating, and reducing the NBI torque by a factor of 2. This latter observation is particularly promising for extension of the scenario to EAST, where maximum power is obtained with balanced NBI injection, and to a reactor, expected to have low rotation. However, modeling of this regime has provided new challenges to state-of-the-art modeling capabilities: quasilinear models can dramatically underpredict the electron transport, and the Sauter bootstrap current can be insufficient. The analysis shows first-principle NEO is in good agreement with experiments for the bootstrap current calculation and ETG modes with a larger saturated amplitude or EM modes may provide the missing electron transport. Work supported in part by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA
Steady State Operation Using Improved ICH and ECH for High Performance Plasma in LHD
Full text: The steady state operation (SSO) of high-performance plasma in LHD has progressed since the last IAEA conference by means of a newly installed ICH antenna (HAS antenna, HAnd Shake type) and an improved ECH system. HAS antenna could control the launched parallel wave number and heated a core plasma efficiently. The heating power of steady state ICH and ECH exceeded 1 MW and 500 kW, respectively, and the higher-density helium plasma with minority hydrogen ions was sustained. Plasma performance improved; e.g., an electron temperature of more than 2 keV at a density of more than 2 x 1019 m-3 became possible for more than 1 min. Dipole phasing operation of the HAS antenna is better than that of monopole operation, and the monopole operation gives almost the same performance with the poloidal array antenna. Three 77 GHz high-power gyrotrons were also installed for high-power ECH in LHD. The frequency of 77 GHz is selected to heat the plasma core region for the wider plasma operation condition, and to increase sustainable plasma density to mitigate the high energetic ion population produced by ICRF wave. The injected power to plasma is finally absorbed by divertor plates, antenna side protectors and the chamber wall. The ratios of heat flow through various channels are estimated and about half of the heat flow goes to the divertor plates, and around 10% is goes to the ICRF antenna protectors. The non-uniform heat flow to the chamber wall decreased from 30% to 15% as the density increased. The particle balance during SSO was also analyzed. The ratio of the total supplied particles (helium and hydrogen) to the externally pumped particles is around 20, which indicates that wall pumping is a dominant particle sink during the SSO of 320 sec. The vacuum chamber works as a large particle sink in LHD. In the case of 54 min plasma operation in 2006, the LHD chamber wall also worked as a particle sink even after the very long operation time. These experiences of steady
The value and stability of the exact steady state solution of the average electron energy balance equation are investigated for three different kinds of homogenuous plasmas heated by a microwave field. These are a weakly ionized plasma, a strongly ionized plasma and a hydrogen plasma in which the collision cross section is approximated by an analytical expression which fits experimental data. The effect of the field frequency and field amplitude on the value and stability of the steady state average electron energy as well as its limiting values are investigated for the three cases considered. (author). 9 figs., 15 refs
Fast Estimation of Plant Steady State, with Application to Static RTO
Rodrigues, Diogo; Amrhein, Michael; Billeter, Julien; Bonvin, Dominique
2016-01-01
In the operation of continuous processes, many tasks require the knowledge of plant steady state at various operating points. This is for example the case in the context of kinetic modeling, response surface modeling and real-time optimization. If the computational techniques are in principle straightforward, the time needed to reach steady state represents the main limiting factor. This work proposes a novel way of speeding up the estimation of plant steady state through...
Superconducting magnets and cryogenics for the steady state superconducting tokamak SST-1
SST-1 is a steady state superconducting tokamak for studying the physics of the plasma processes in tokamak under steady state conditions and to learn technologies related to the steady state operation of the tokamak. SST-1 will have superconducting magnets made from NbTi based conductors operating at 4.5 K temperature. The design of the superconducting magnets and the cryogenic system of SST-1 tokamak are described. (author)
Aslan Sabahaldeen Jalal Abdi
2011-01-01
The objective of this work is to investigate the performance of a conventional three phase induction motor supplied by unbalanced voltages. An effort to study the motor steady state performance under this disturbance is introduced. Using per phase equivalent circuit analysis with the concept of symmetrical components approach, the steady state performance is theoretically calculated. Also, a model for the induction motor with the MATLAB/Simulink SPS tools has been implemented and steady state...
A Review of Fusion and Tokamak Research Towards Steady-State Operation: A JAEA Contribution
Mitsuru Kikuchi
2010-01-01
Providing a historical overview of 50 years of fusion research, a review of the fundamentals and concepts of fusion and research efforts towards the implementation of a steady state tokamak reactor is presented. In 1990, a steady-state tokamak reactor (SSTR) best utilizing the bootstrap current was developed. Since then, significant efforts have been made in major tokamaks, including JT-60U, exploring advanced regimes relevant to the steady state operation of tokamaks. In this paper, the fund...
Steady State Analysis of Multiple Effect Evaporation (MEE) Desalination Process
Life without water is not possible. Like other natural resources, the global resources of fresh water are unevenly distributed. The world population is increasing at very rapid rate while the natural water resources remain constant. This gap is expected to widen dramatically in the near future. Our country like most countries in the east suffer from water stressed condition. Desalination is only the logical or available solution. In MED units, the feed seawater sprayed individually in each effect is heated to form pure vapors, which condense to form product water. Irrespective of the continuous development of the desalination industry the thermal desalination is still expensive. The study presented in this thesis is motivated by, to study the impact of various cost controlling parameters on the performance of MEE desalination process. KANUPP has two desalination plants (RO and NDDP). The NDDP has parallel feed cross flow multiple effect evaporation (MEE-PC) configurations. The study presented in this thesis describes a simplified steady state mathematical model to analyze the MED systems. The results obtained by the model are compared with the NDDP data. The developed model is used to investigate the effect of the parameters controlling the product water cost. These parameters includes thermal performance ratio, cooling water flow rate and heat transfer area. It can also be used to study the effect of variation in the operating conditions of the plant on the plant performance. The effect of the process variables on the performance of MED is carried out. This includes the effect of number of effects, intake seawater salinity and heating stream temperature, vacuum condition in term of vapor temperature of last effect. (author)
Kinematical Analysis along Maximal Lactate Steady State Swimming Intensity
Figueiredo, Pedro; Nazario, Rafael; Sousa, Marisa; Pelarigo, Jailton Gregório; Vilas-Boas, João Paulo; Fernandes, Ricardo
2014-01-01
The purpose of this study was to conduct a kinematical analysis during swimming at the intensity corresponding to maximal lactate steady state (MLSS). Thirteen long distance swimmers performed, in different days, an intermittent incremental protocol of n x 200 m until exhaustion and two to four 30-min submaximal constant speed bouts to determine the MLSS. The video analysis, using APAS System (Ariel Dynamics Inc., USA), allowed determining the following relevant swimming determinants (in five moments of the 30-min test: 0, 25, 50, 75, and 100%): stroke rate, stroke length, trunk incline, intracyclic velocity variation, propelling efficiency, index of coordination and the time allotted to propulsion per distance unit. An ANOVA for repeated measures was used to compare the parameters mean values along each moment of analysis. Stoke rate tended to increase and stroke length to decrease along the test; a tendency to decrease was also found for intracyclic velocity variation and propelling efficiency whereas the index of coordination and the propulsive impulse remained stable during the MLSS test. It can be concluded that the MLSS is not only an intensity to maintain without a significant increase of blood lactate concentration, but a concomitant stability for some biomechanical parameters exists (after an initial adaptation). However, efficiency indicators seem to be more sensitive to changes occurring during swimming at this threshold intensity. Key Points In MLSS swimming intensity, stability of the stroke length and stroke frequency occurs after an initial adaptation. Efficiency indicators seem to be more sensitive to possible changes occurring through time at MLSS intensity. MLSS is a useful and practical swimming intensity to be maintained for a long period of time, but some constraints in technique can occur. PMID:25177189
Impact of aquifer desaturation on steady-state river seepage
Morel-Seytoux, Hubert J.; Miracapillo, Cinzia; Mehl, Steffen
2016-02-01
Flow exchange between surface and ground water is of great importance be it for beneficial allocation and use of the water resources or for the proper exercise of water rights. That exchange can take place under a saturated or unsaturated flow regime. Which regimes occur depend on conditions in the vicinity of the interactive area. Withdrawals partially sustained by seepage may not bring about desaturation but greater amounts eventually will. The problem considered in this paper deals only with the steady-state case. It is meant as a first step toward a simple, yet accurate and physically based treatment of the transient situation. The primary purpose of the article is to provide simple criteria for determination of the initiation of desaturation in an aquifer originally in saturated hydraulic connection with a river or a recharge area. The extent of the unsaturated zone in the aquifer will increase with increasing withdrawals while at the same time the seepage rate from the river increases. However the seepage increase will stop once infiltration takes place strictly by gravity in the aquifer and is no longer opposed by the capillary rise from the water table below the riverbed. Following desaturation simple criteria are derived and simple analytical formulae provided to estimate the river seepage based on the position of the water table mound below the clogging layer and at some distance away from the river bank. They fully account for the unsaturated flow phenomena, including the existence of a drainage entry pressure. Two secondary objectives were to verify that (1) the assumption of uniform vertical flow through a clogging layer and that (2) the approximation of the water table mound below the seepage area as a flat surface were both reasonably legitimate. This approach will be especially advantageous for the implementation of the methodology in large-scale applications of integrated hydrologic models used for management.
Dehghani, Hossein; Mitra, Aditi
2016-06-01
Results are presented for an open Floquet topological system represented by Dirac fermions coupled to a circularly polarized laser and an external reservoir. It is shown that when the separation between quasienergy bands becomes small, and comparable to the coupling strength to the reservoir, the reduced density matrix in the Floquet basis, even at steady state, has nonzero off-diagonal elements, with the magnitude of the off-diagonal elements increasing with the strength of the coupling to the reservoir. In contrast, the coupling to the reservoir only weakly affects the diagonal elements, hence inducing an effective coherence. The steady-state reduced density matrix synchronizes with the periodic drive, and a Fourier analysis allows the extraction of the occupation probabilities of the Floquet quasienergy levels. The lack of detailed balance at steady state is quantified in terms of an entropy-production rate, and it is shown that this equals the heat current flowing out of the system and into the reservoir. It is also shown that the entropy-production rate mainly depends on the off-diagonal components of the Floquet density matrix. Thus, a stronger coupling to the reservoir leads to an enhanced entropy-production rate, implying a more efficient removal of heat from the system, which in turn helps the system maintain coherence. Analytic expressions in the vicinity of the Dirac point are derived which highlights these results, and also indicates how the reservoir may be engineered to enhance the coherence of the system.