Synthesis of high viscosity index base stock and study on the lubricating properties

2016 ◽  
Vol 68 (1) ◽  
pp. 52-56 ◽  
Author(s):  
Weiwei Wang ◽  
Shan Jiang ◽  
Yan Shen ◽  
Shunba Xia ◽  
Jiujun Xu

Purpose – This paper aims to address the polymerization of 1-decene by [Emim]Cl/AlCl3 ionic liquid and the film-forming properties of the product compared with commercially available base stocks. Design/methodology/approach – Experiments were carried out to investigate the influence of [Emim]Cl/AlCl3 mole ratio, catalyst dosage, reaction temperature, reaction time and water on the polyreaction. Poly alpha-olefin (PAO) is prepared under optimal reaction condition. Film-forming properties of PAO have been compared with those of Group I, Group II and Group III base stocks, which are selected with approximately the same viscosity. Findings – Experimental results show that after a 4-h reaction time, yield of PAO can be higher than 85 per cent and viscosity index can be up to 160 with [Emim] Cl/AlCl3 mole ratio of 2:1, catalyst dosage of 3 per cent wt. and water content of 20 ppm. A strong influence of water on reaction is observed. With approximately the same viscosity, PAO shows the superiority in film thickness at low-sliding speeds compared with Group I and Group II base stocks. At high temperature, PAO provides a thicker film than other base stocks. Originality/value – In recent years, there has been considerable interest in ionic liquids. As a novel catalyst, it has so many advantages including low corrosion, low toxicity, low cost and a potentially wide range of properties compared with traditional catalysts. This paper reports the polymerization of 1-decene by [Emim]Cl/AlCl3 ionic liquid and the study on lubricating properties of PAO compared with mineral base stocks.

1998 ◽  
Vol 89 (3) ◽  
pp. 359-365 ◽  
Author(s):  
Andres M. Lozano ◽  
Graham Vanderlinden ◽  
Robert Bachoo ◽  
Peter Rothbart

Object. The authors evaluated the effectiveness of microsurgical C-2 ganglionectomy in 39 patients with medically refractory chronic occipital pain. In this procedure the neurons transmitting sensory inputs from the occiput are removed and, unlike peripheral nerve ablation, axonal regeneration is not possible. Methods. The patients in this series had symptoms for 1 to 43 years. In 22 patients the occipital pain was caused by trauma; in 17 patients the pain was spontaneous. Pain relief failed in 17 patients who had undergone a previous occipital neurectomy or C-2 rhizolysis. Twenty-three patients experienced pain that was described as shocklike, electric, shooting, jabbing, stabbing, sharp, or exploding (Group I). Eight patients described their pain as dull, pounding, aching, throbbing, or pressurelike (Group II). The patients underwent unilateral or bilateral C-2 open microsurgical ganglionectomies. The postoperative follow-up period ranged from 19 to 48 months. Nineteen patients experienced an excellent result (> 90% reduction in pain). Pain caused by trauma or that described using Group I terms responded best to ganglionectomy (80% good or excellent response). In contrast, the majority of the patients with nontraumatic pain or those described using Group II descriptors did not achieve favorable results. Conclusions. The authors conclude that: 1) patients who suffer from chronic occipital pain after having sustained injury obtain worthwhile benefit from microsurgical C-2 ganglionectomy; 2) patients suffering from migraine, tension, and vascular headaches involving the occipital area are most often not helped by this operation; and 3) terms such as “shock,” “electric,” “shooting,” “jabbing,” and “sharp” used to describe occipital pain predict a favorable pain outcome following a C-2 ganglionectomy.


2013 ◽  
Vol 79 (12) ◽  
pp. 3860-3863 ◽  
Author(s):  
Jinshui Zheng ◽  
Donghai Peng ◽  
Xiaoling Song ◽  
Lifang Ruan ◽  
Jacques Mahillon ◽  
...  

ABSTRACTcsaBgene analysis clustered 198 strains ofBacillus anthracis,Bacillus cereus, andBacillus thuringiensisinto two groups related to mammalian and insect hosts, respectively. Mammal-related group I strains also have more S-layer homology (SLH) protein genes than group II strains. This indicates thatcsaB-based differentiation reflects selective pressure from animal hosts.


1999 ◽  
Vol 90 (3) ◽  
pp. 448-454 ◽  
Author(s):  
Giuseppe Cinalli ◽  
Christian Sainte-Rose ◽  
Paul Chumas ◽  
Michel Zerah ◽  
Francis Brunelle ◽  
...  

Object. The goal of this study was to analyze the types of failure and long-term efficacy of third ventriculostomy in children.Methods. The authors retrospectively analyzed clinical data obtained in 213 children affected by obstructive triventricular hydrocephalus who were treated by third ventriculostomy between 1973 and 1997. There were 120 boys and 93 girls. The causes of the hydrocephalus included: aqueductal stenosis in 126 cases; toxoplasmosis in 23 cases, pineal, mesencephalic, or tectal tumor in 42 cases; and other causes in 22 cases. In 94 cases, the procedure was performed using ventriculographic guidance (Group I) and in 119 cases by using endoscopic guidance (Group II). In 19 cases (12 in Group I and seven in Group II) failure was related to the surgical technique. Three deaths related to the technique were observed in Group I. For the remaining patients, Kaplan—Meier survival analysis showed a functioning third ventriculostomy rate of 72% at 6 years with a mean follow-up period of 45.5 months (range 4 days–17 years). No significant differences were found during long-term follow up between the two groups. In Group I, a significantly higher failure rate was seen in children younger than 6 months of age, but this difference was not observed in Group II. Thirty-eight patients required reoperation (21 in Group I and 17 in Group II) because of persistent or recurrent intracranial hypertension. In 29 patients shunt placement was necessary. In nine patients in whom there was radiologically confirmed obstruction of the stoma, the third ventriculostomy was repeated; this was successful in seven cases. Cine phase-contrast (PC) magnetic resonance (MR) imaging studies were performed in 15 patients in Group I at least 10 years after they had undergone third ventriculostomy (range 10–17 years, median 14.3 years); this confirmed long-term patency of the stoma in all cases.Conclusions. Third ventriculostomy effectively controls obstructive triventricular hydrocephalus in more than 70% of children and should be preferred to placement of extracranial cerebrospinal shunts in this group of patients. When performed using ventriculographic guidance, the technique has a higher mortality rate and a higher failure rate in children younger than 6 months of age and is, therefore, no longer preferred. When third ventriculostomy is performed using endoscopic guidance, the same long-term results are achieved in children younger than 6 months of age as in older children and, thus, patient age should no longer be considered as a contraindication to using the technique. Delayed failures are usually secondary to obstruction of the stoma and often can be managed by repeating the procedure. Midline sagittal T2-weighted MR imaging sequences combined with cine PC MR imaging flow measurements provide a reliable tool for diagnosis of aqueductal stenosis and for ascertaining the patency of the stoma during follow-up evaluation.


1993 ◽  
Vol 78 (6) ◽  
pp. 959-965 ◽  
Author(s):  
Vittorio M. Morreale ◽  
Barbara H. Herman ◽  
Violette Der-Minassian ◽  
Miklós Palkovits ◽  
Phillip Klubes ◽  
...  

✓ A tumor model involving stereotactically implanted culture-reared tumor cells is presented. Stainless steel cannulas were stereotactically and permanently implanted into the caudate nucleus of 30 rats. The animals were separated into two groups. In Group I, 15 animals received a 10-µl injection containing 106 C6 glioblastoma cells (five rats), 106 Walker 256 breast carcinoma cells (five rats), or cell medium (five rats). The coordinates were A(+1.5), L(+3.0), and DV(−5.0). In Group II, the coordinates were changed to A(+1.0), L(+3.0), and DV(−5.0) and the same number of rats received a 1-µl injection containing 105 cells of each tumor in an attempt to produce more focal tumors. Two weeks after implantation, brain sections were stained with cresyl violet and a subset was stained for glial fibrillary acidic protein (GFAP). A computerized morphometric analysis system was used to quantify tumor size. In Group I, the mean C6 tumor areas (± standard error of the mean) at specific coordinates were (in sq mm): A(+4.7) 0.4 ± 0.2; A(+3.7) 3.5 ≥ 1.1; A(+2.7) 5.7 ± 1.7; A(+1.7) 9.5 ± 2.3; A(+0.7) 7.5 ± 3.2; A(−0.3) 3.7 ± 2.9; and A(−1.3) 0.3 ± 0.3. A nearly identical tumor mass and extension into the brain was produced in rats injected with Walker 256 cells. Similar C6 tumor areas were indicated in adjacent sections stained with cresyl violet and GFAP. Tumor was found in the caudate nucleus in all 10 rats, but not in the nucleus accumbens, fornix, or hippocampus. In Group II animals, tumor magnitude and extension into the brain were greatly reduced. The 106 cells in the 10-µl volume was the most reliable tumor load for obtaining uniform tumors in different animals. The similarity of tumor distribution across different animals was indicated by the low variance of tumor area at specific anteroposterior coordinates. Reproducible and well-circumscribed caudate nucleus tumors were produced using this stereotactic procedure.


1996 ◽  
Vol 85 (5) ◽  
pp. 923-928 ◽  
Author(s):  
Carlos A. David ◽  
Ricardo Prado ◽  
W. Dalton Dietrich

✓ Temporary arterial occlusion has been routinely used as an adjunct in intracranial aneurysm surgery. This has commonly been performed using a protocol of multiple short periods of occlusion alternating with periods of restoration of normal circulation. Recently, the logical basis of this method has come under scrutiny. There is extensive experimental evidence to suggest that repetitive, brief periods of global ischemia may cause more severe cerebral injury than an equivalent single period of global ischemia. Only recently has this issue begun to be addressed with regard to focal ischemia. Hence, despite the common use of temporary clipping, little experimental data are available regarding the ischemic consequences of temporary arterial occlusion with periods of reperfusion versus uninterrupted temporary occlusion. To investigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of focal ischemia. Sixteen anesthetized Sprague—Dawley rats were divided into two groups. The animals in Group I underwent 60 minutes of uninterrupted middle cerebral artery occlusion and the animals in Group II were subjected to six separate 10-minute occlusion periods with 5 minutes of reperfusion between occlusions. Histopathological analysis was performed 72 hours postischemia. Group I had significantly increased mean infarction volumes (50.0 ± 12.1 mm3) compared to Group II (8.7 ± 3.1 mm3) (p = 0.008). Injuries in Group I occurred in both the cortex and striatum, whereas Group II showed only striatal injuries. Furthermore, the extent of the injuries in Group II was less severe, characterized by ischemic neuronal injury rather than frank infarction. The results indicate that intermittent reperfusion is neuroprotective during temporary focal ischemia and support the hypothesis that intermittent reperfusion is beneficial if temporary clipping is required during aneurysm repair.


1988 ◽  
Vol 69 (6) ◽  
pp. 869-876 ◽  
Author(s):  
Patrick Ravussin ◽  
Mounir Abou-Madi ◽  
David Archer ◽  
René Chiolero ◽  
James Freeman ◽  
...  

✓ In view of the current concern that rapid infusion of mannitol might initially aggravate intracranial hypertension, the effects of a mannitol infusion on lumbar cerebrospinal fluid pressure (CSFP) were investigated in 49 patients. The studies were performed when the patients were under general anesthesia prior to elective craniotomy for tumor resection or intracerebral aneurysm clipping. The patients were divided into two groups: 24 patients with normal CSFP (Group I, mean CSFP 10.5 mm Hg) and 25 with raised CSFP (Group II, mean CSFP 20.8 mm Hg). Measurements of CSFP, mean arterial blood pressure (MABP), and central venous pressure (CVP) were made serially during and after the infusion of 20% mannitol (1 gm ⋅ kg−1 infused over a 10-minute interval). In both groups, mannitol infusion provoked a fall in MABP and an increase in CVP. An immediate increase in CSFP was observed in Group II, whereas CSFP increased transiently but significantly in Group I. Analysis of the arterial and venous driving pressures which contribute to CSFP suggests that the transient increase in CSFP after mannitol in Group I was partly due to the increase in CVP. The presence of intracranial hypertension may thus alter the CSFP response to arterial and venous pressure changes. Cerebral blood volume (CBV) was measured in dogs in a separate study analogous to the human protocol. The CBV increased approximately 25% over control values after mannitol infusion both in the normal animals and in those with CSFP raised by an epidural balloon. The response of the CSFP to mannitol infusion differed between both groups in a fashion similar to that observed in the human subjects. Thus, differences in CBV changes after mannitol do not account for the difference in CSFP response between normal subjects and those with raised CSFP.


2001 ◽  
Vol 95 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Yoichi Katayama ◽  
Masahiko Kasai ◽  
Hideki Oshima ◽  
Chikashi Fukaya ◽  
Takamitsu Yamamoto ◽  
...  

Object. A blinded evaluation of the effects of subthalamic nucleus (STN) stimulation was performed in levodopaintolerant patients with Parkinson disease (PD). These patients (Group I, seven patients) were moderately or severely disabled (Hoehn and Yahr Stages III–V during the off period), but were receiving only a small dose of medication (levodopa-equivalent dose [LED] 0–400 mg/day) because they suffered unbearable side effects. The results were analyzed in comparison with those obtained in patients with advanced PD (Group II, seven patients) who were severely disabled (Hoehn and Yahr Stages IV and V during the off period), but were treated with a large dose of medication (500–990 mg/day). Methods. The patients were evaluated twice at 6 to 8 months after surgery. To determine the actual benefits afforded by STN stimulation to their overall daily activities, the patients were maintained on their medication regimen with optimal doses and schedules. Stimulation was turned off overnight for at least 12 hours. It was turned on in the morning (or remained turned off), and each patient's best and worst scores on the Unified Parkinson's Disease Rating Scale during waking daytime activity were recorded as on- and off-period scores, respectively. The order of assessment with respect to whether stimulation was occurring was determined randomly. The STN stimulation markedly improved daily activity and total motor scores in Group I patients. The percentage time of immobility (Hoehn and Yahr Stages IV and V) became 0% in patients who were intermittently immobile while not receiving stimulation. Improvements were demonstrated in tremor, rigidity, akinesia, and gait subscores. The STN stimulation produced less marked but still noticeable improvements in the daily activity and total motor scores in Group II patients. The percentage time of immobility as well as the LED was reduced in patients who displayed intermittent immobility with pronounced motor fluctuations while not receiving stimulation. Improvements were demonstrated in tremor, rigidity, and dyskinesia subscores in these patients. In contrast, STN stimulation did not improve the overall daily activities at all in patients who had become unresponsive to a tolerable dose of levodopa and were continuously immobile, even though these patients' tremor and rigidity subscores were still improved by stimulation. Conclusions. Consistent with earlier findings, the great benefit of STN stimulation in levodopa-intolerant patients is that STN stimulation can reduce the level of required levodopa medication. This suggests that STN stimulation could be a therapeutic option for patients with less-advanced PD by allowing levodopa medication to be maintained at as low a dose as possible, and to prevent adverse reactions to the continued use of large-dose levodopa.


mBio ◽  
2019 ◽  
Vol 10 (3) ◽  
Author(s):  
Kelley Hurst-Hess ◽  
Rajesh Biswas ◽  
Yong Yang ◽  
Paulami Rudra ◽  
Erica Lasek-Nesselquist ◽  
...  

ABSTRACTMycobacterial σBbelongs to the group II family of sigma factors, which are widely considered to transcribe genes required for stationary-phase survival and the response to stress. Here we explored the mechanism underlying the observed hypersensitivity of ΔsigBdeletion mutants ofMycobacteriumsmegmatis,M. abscessus, andM. tuberculosisto rifampin (RIF) and uncovered an additional constitutive role of σBduring exponential growth of mycobacteria that complements the function of the primary sigma factor, σA. Using chromatin immunoprecipitation sequencing (ChIP-Seq), we show that during exponential phase, σBbinds to over 200 promoter regions, including those driving expression of essential housekeeping genes, like the rRNA gene. ChIP-Seq of ectopically expressed σA-FLAG demonstrated that at least 61 promoter sites are recognized by both σAand σB. These results together suggest that RNA polymerase holoenzymes containing either σAor σBtranscribe housekeeping genes in exponentially growing mycobacteria. The RIF sensitivity of the ΔsigBmutant possibly reflects a decrease in the effective housekeeping holoenzyme pool, which results in susceptibility of the mutant to lower doses of RIF. Consistent with this model, overexpression of σArestores the RIF tolerance of the ΔsigBmutant to that of the wild type, concomitantly ruling out a specialized role of σBin RIF tolerance. Although the properties of mycobacterial σBparallel those ofEscherichiacoliσ38in its ability to transcribe a subset of housekeeping genes, σBpresents a clear departure from theE. coliparadigm, wherein the cellular levels of σ38are tightly controlled during exponential growth, such that the transcription of housekeeping genes is initiated exclusively by a holoenzyme containing σ70(E.σ70).IMPORTANCEAll mycobacteria encode a group II sigma factor, σB, closely related to the group I principal housekeeping sigma factor, σA. Group II sigma factors are widely believed to play specialized roles in the general stress response and stationary-phase transition in the bacteria that encode them. Contrary to this widely accepted view, we show an additional housekeeping function of σBthat complements the function of σAin logarithmically growing cells. These findings implicate a novel and dynamic partnership between σAand σBin maintaining the expression of housekeeping genes in mycobacteria and can perhaps be extended to other bacterial species that possess multiple group II sigma factors.


1992 ◽  
Vol 76 (6) ◽  
pp. 1029-1031 ◽  
Author(s):  
Edward C. Benzel ◽  
Jay P. Mashburn ◽  
Steven Conrad ◽  
Denise Modling

✓ The absence of spontaneous respirations at a PaCO2 of 60 mm Hg or above has traditionally been accepted as the respiratory criteria for the determination of brain death. The testing of patients for the presence or absence of apnea has been complicated because the rate of PaCO2 elevation may vary substantially from patient to patient, and a nonlinear relationship exists between the rate of PaCO2 increase and the duration of apnea. In an attempt to refine the apnea test and to further elucidate the physiology of hypercapnia in humans, 11 patients who met all but the respiratory criteria for brain death were evaluated using a modification of a previously utilized apnea testing protocol. All patients were brought to a PaCO2 of 40 mm Hg or above prior to the apnea test. Baseline PaCO2 ranged from 40 to 45 mm Hg in six patients (Group I) and from 46 to 51 mm Hg in five patients (Group II). The mean rate of PaCO2 increase was 5.1 ± 1.4 mm Hg/min in Group I and 6.7 ± 3.1 mm Hg/min in Group II. No problems with cardiovascular instability or hypoxia were encountered during testing in this series. This refinement of the apnea test allows for a streamlined and safe approach to brain death detection.


2000 ◽  
Vol 93 (2) ◽  
pp. 305-314 ◽  
Author(s):  
Susan A. Stern ◽  
Brian J. Zink ◽  
Michelle Mertz ◽  
Xu Wang ◽  
Steven C. Dronen

Object. Studies of isolated uncontrolled hemorrhage have indicated that initial limited resuscitation improves survival. Limited resuscitation has not been studied in combined traumatic brain injury and uncontrolled hemorrhage. In this study the authors evaluated the effects of limited resuscitation on outcome in combined fluid-percussion injury (FPI) and uncontrolled hemorrhage.Methods. Twenty-four swine weighing 17 to 24 kg each underwent FPI (3 atm) and hemorrhage to a mean arterial pressure (MAP) of 30 mm Hg in the presence of a 4-mm aortic tear. Group I (nine animals) was initially resuscitated to a goal MAP of 60 mm Hg; Group II (nine animals) was resuscitated to a goal MAP of 80 mm Hg; and Group III (control; six animals) was not resuscitated. After 60 minutes, the aortic hemorrhage was controlled and the animals were resuscitated to baseline physiological parameters and observed for 150 minutes.Mortality rates were 11%, 50%, and 100% for Groups I, II, and III, respectively (Fisher's exact test; p = 0.002). The total hemorrhage volume was greater in Group II (69 ± 32 ml/kg), as compared with Group I (41 ± 18 ml/kg) and Group III (37 ± 3 ml/kg) according to analysis of variance (p < 0.05). In surviving animals, cerebral perfusion pressure, cerebral blood flow (CBF), cerebral venous O2 saturation (ScvO2), and cerebral metabolic rate of O2 did not differ among groups. Although CBF was approximately 50% of baseline during the period of limited resuscitation in Group I, ScvO2 remained greater than 60%, and arteriovenous O2 differences remained within normal limits.Conclusions. In this model of FPI and uncontrolled hemorrhage, early aggressive resuscitation, which is currently recommended, resulted in increased hemorrhage and failure to optimize cerebrovascular parameters. In addition, a 60-minute period of moderate hypotension (MAP = 60 mm Hg) was well tolerated and did not compromise cerebrovascular hemodynamics, as evidenced by physiological parameters that remained within the limits of cerebral autoregulation.


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