Modular synthesis of Petri nets for modeling flexible manufacturing systems

This paper proposes a modular Petri net synthesis method for modeling flexible manufacturing systems based on synchronization among control processes of the manufacturing resources (such as robots and machines). In the method, the target system is modeled in a bottom-up and uniform manner by first describing the system's control processes using strongly connected state machines (SCSMs) as the basic modules. Each SCSM may contain multiple tokens to represent resources from the same type such as spaces in a buffer. Next, the common transitions and common transition subnets of the modules are merged to represent their synchronization. The system model constructed is proven to be conservative and thus bounded. Moreover, a restricted class of merged nets is proven to be live and reversible. For general classes of merged nets, this paper shows theorems that easily calculateP-invariants of the final net without solving the linear system equations. TheseP-invariants can be used to help in verifying the model's qualitative properties such as liveness.     

An immunoenzymatic method for improving the sensitivity of antigen measurement by electroimmunodiffusion techniques. Application to the quantification of human alpha-fetoprotein.

A double antibody technique of electroimmunodiffusion, which uses glucose oxidase-labelled sheep antibodies to rabbit immunoglobulins as second antibody, is described. Primary antigen-antibody reaction is carried out with a rabbit antiserum by electroimmundiffusion. The glucose oxidase-labelled immunoreagent, being of general application, can serve for the quantification of different antigens and is here used for measurement of low levels of human alpha-fetoprotein. Reproducible results in the range of 50-800 ng/ml were obtained with a variation coefficient of 5 to 10%.     

Formyleleganolone and bibifuran,two metabolites from the brown alga Bifurcaria bifurcata

Two new diterpenoids formyleleganolone (1) and bibifuran (2) were isolated from a sample of the brown alga Bifurcaria bifurcata collected near Roscoff (Brittany, France). The structures of the new compounds were established on the basis of 1D and 2D NMR spectroscopic and mass spectrometric (ESI and EI) analyses. Formyleleganolone (1) is derived from eleganolone (4) by formylation of the hydroxy group. Bibifuran (2) has been identified as a new furan derivative of 4. Additionally, the diterpenoid 16-hydroxygeranylgeraniol (3) is reported for the first time from this species.     

Evaluation of potential sustainability of deep-sea fisheries for grenadiers (Macrouridae)

The ability of six grenadier species from the North Atlantic, North Pacific, and Southern Ocean to sustain deep-sea fisheries is assessed. These species are captured in high amounts as bycatch and a few are taken in targeted fisheries, yet population status for most is poorly known or known for only a small portion of their range. A productivity and susceptibility analysis showed that none of the species was highly productive, which was not unexpected given their life history characteristics. While grenadiers were ranked more vulnerable than species in the northeastern Pacific groundfish fisheries, none of the investigated species was ranked as highly susceptible or heavily exploited. This result exposed several weaknesses in the PSA technique and attribute scoring. Management actions and regulations are discussed, which, if employed, might make grenadier fisheries sustainable.     

Conditions for growing Mycoplasma canadense and Mycoplasma verecundum in a serum-free medium

Mycoplasma canadense and Mycoplasma verecundum were cultured in a serum-free medium containing bovine serum albumin, cholesterol, oleic acid, and palmitic acid in order to avoid the addition of horse serum. Growth was detected by measurement of A640 and by colony formation. The level of growth attained in this medium was less than that obtained in the horse serum-supplemented media, but colonies retained their distinctive morphology.     

Osmotic fragility of chromaffin granules prepared under isoosmotic or hyperosmotic conditions and localization of acetylcholinesterase

In chromaffin cells of the adrenal medulla, catecholamines are stored in secretory granules. Different methods have been described to purify chromaffin granules. In the present study, storage granules were prepared using isoosmotic self-generating Percoll gradients or hyperosmotic sucrose gradients, and a comparison of their physical properties in response to osmotic changes was made. Catecholamines, dopamine beta-hydroxylase activity and protein were detected both in the external medium and in the granule fraction according to the medium osmolality. Suspension turbidity was used as a measure of organelle integrity. Acetylcholinesterase activity was found to be associated with both isoosmotically and hyperosomotically prepared granules. The total acetylcholinesterase activity was determined after adding Triton X-100 to the assay medium. When adrenal medullary tissue was homogenized in buffers containing echothiopate, an inhibitor of acetylcholinesterase, only 15-20% of enzyme activity was inhibited, excluding the possibility that main granule acetylcholinesterase could be due to contamination by plasma membrane fragments, endoplasmic reticulum and Golgi membranes. When granules were suspended in hypoosmotic buffers, a soluble acetylcholinesterase form was released into the external medium, while an insoluble acetylcholinesterase form was still found associated with the membrane fraction. Soluble acetylcholinesterase was found to be released differently than soluble dopamine beta-hydroxylase, indicating that acetylcholinesterase may be associated with a more osmotically resistant granule population.     

缺氧大鼠心肌α1,β肾上腺素能受体的变化

为了探讨α_1、β肾上腺素能受体在大鼠缺氧性心脏肥大进程中的作用,本研究应用放射配基结合法观察了不同缺氧时间大鼠心室α_1、β肾上腺素能受体变化的动态过程,同时也观察了α_1、β受体阻断剂在预防缺氧性心肌肥大发生中的作用。缺氧10d后,测定右心室重量及组织学检查未见右心室肥大,但此时心室肌α_1受体数量从对照组的27.49±1.25增加到33.80±0.90fmol/mg蛋白(P<0.05);β受体从对照组的51.80±7.60下降到25.10±2.30fmol/mg蛋白(P<0.01)。缺氧20和30d后α_1受体进一步增加到40.70±1.43和32.30±1.96fmol/mg蛋白(P<0.05);β受体分别为27.90±2.30和42.80±1.70fmol/mg蛋白(P<0.05)。缺氧20和30d后右心室重量指数明显高于对照组,在整个缺氧过程中α_1、β受体的亲和性(K_d)未见明显变化,未见左心室肥大。缺氧同时应用α_1受体阻断剂(哌唑嗪4mg·kg~(-1)·d~(-1))30d,可明显预防缺氧所致的右心肥大;而β受体阻断剂(心得安10mg·kg~(-1)·d~(-1))没有此种作用。由此可见,在缺氧所致右心肥大之前,心肌α_1受体数量即明显升高,α_1受体阻断剂可以预防缺氧引起的右心肥大。     

Vanadate stimulates system A amino acid transport activity in skeletal muscle. Evidence for the involvement of intracellular pH as a mediator of vanadate action.

Sodium orthovanadate caused a 2-fold stimulation of system A transport activity in soleus muscle, as assessed by the uptake of the nonmetabolizable analog 2-(methylamino)isobutyric acid (MeAIB). The effect of vanadate on system A was rapid, concentration-dependent and was characterized by an increased Vmax without modification of Km for MeAIB. Under these conditions, vanadate also activated 3-O-methylglucose uptake and lactate production. The effects of vanadate on muscle metabolism showed a complex interaction with the effects of insulin. Thus, the stimulatory effects of vanadate and insulin on MeAIB and 3-O-methylglucose uptake were not additive; however, the effects of insulin and vanadate on lactate production were additive. In spite of the lack of additivity, insulin- and vanadate-induced stimulation of system A differed in their sensitivity to gramicidin D, being the vanadate effect more susceptible to inhibition by gramicidin D than the insulin effect. System A transport activity shows a dependence on pH, and recent results suggest the presence of critical histidine residues on the A carrier that may be responsible for its pH dependence (Bertran, J., Roca, A., Pola, E., Testar, X., Zorzano, A. & Palacín, M. (1991) J. Biol. Chem. 266, 798-802). In this regard, a rise in extracellular pH led to a substantial activation of system A. Furthermore, lowering of muscle intracellular pH induced by ethylisopropylamiloride (EIPA), a specific inhibitor of sodium/proton exchange activity, led to inhibition of system A. This suggests that critical histidine residues are present in an intracellular localization on the A carrier. Furthermore, the rate of muscle glycolysis was also altered in response to a rise in extracellular pH or to EIPA treatment. Regarding the mechanisms involved in vanadate action, vanadate treatment in the incubated soleus muscle did not cause any significant stimulation of tyrosine kinase activity after partial purification of muscle insulin receptors. On the other hand, vanadate but not insulin caused a substantial increase in muscle intracellular pH as assessed by 5,5'-dimethyloxazolidine-2,4-dione equilibrium. This effect of vanadate on intracellular pH was not due to activation of the sodium/proton exchanger, since it was not blocked by EIPA. Based on these findings, we suggest that alkalinization of muscle intracellular pH might mediate the effects of vanadate on system A and on glycolysis.     

Ageing-related changes in Mycoplasma canadense membranes.

Fluidity and composition of cell membranes during progression of Mycoplasma canadense cultures grown in a serum-free medium was assessed. The fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at 25 degrees C of intact cells and liposomes in the exponential and stationary phases of growth was compared. A decrease in fluidity and an increase in the ratio of saturated to unsaturated fatty acids was detected in cell membranes on aging. Nevertheless, membrane density remained unaltered although the molar ratio of cholesterol to phospholipids decreased. It is proposed that the increase in lipid order is primarily due to the increase in the ratio of saturated to unsaturated membrane fatty acids, being the diminished molar ratio of cholesterol to phospholipids involved in the reduced unsaturated fatty acid uptake.