A reduced-order-model-based equivalent circuit for piezoelectric micro-electro-mechanical-system loudspeakers modeling

Piezoelectric micro-electro-mechanical-system (MEMS) speakers are emerging as promising implementations of loudspeakers at the microscale, as they are able to meet the ever-increasing requirements for modern audio devices to become smaller, lighter, and integrable into digital systems. In this work, we propose a finite element model (FEM)-assisted lumped-parameters equivalent circuit for a fast and accurate modeling of these types of devices. The electro-mechanical parameters are derived from a pre-stressed FEM eigenfrequency analysis, to account for arbitrarily complex geometries and for the shift of the speaker resonance frequency due to an initial non-null pre-deflected configuration. The parameters of the acoustical circuit are instead computed through analytical formulas. The acoustic short-circuit between the speaker front and rear sides is taken into account through a proper air-gaps modeling. The very good matching in terms of radiated sound pressure level among the equivalent circuit predictions, FEM simulations, and experimental data proves the ability of the proposed method to accurately simulate the speaker performance. Moreover, due to its generality, it represents a versatile tool for designing piezoelectric MEMS speakers.

Leptin: a review of its peripheral actions and interactions

Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain.

Characterization of leptin binding in bovine kidney membranes

The interactions of leptin with its receptor and other leptin binding sites is not well described or understood. We have used Scatchard analysis of saturation binding data to characterize the affinity of leptin for binding sites in bovine kidney membranes. 125I-Leptin was used in saturation studies, over a range of concentrations from 50 pM to 9 nM. 125I-Leptin differentiated a high affinity binding site from an abundant low affinity site. The high affinity/low density binding site (putative leptin receptor) had K(d)=0.098 nM and B(max)=46.2f mol/mg protein. An additional class of low affinity, highly abundant sites with an apparent K(d)=175 nM, and B(max)=574 fmol/mg protein was characterized. The association and dissociation kinetics for 125I-leptin binding were also studied. Dissociation of the leptin-receptor complex was very rapid, and this necessitated the use of a specially developed separation method for radioligand binding studies (precipitation with PEG and filtration). Competitive displacement of 125I-leptin by mouse and human leptin and polyclonal anti-bovine leptin antibodies was dose-dependent. Specificity of binding was shown as bound 125I-leptin was not displaced by insulin or control antibodies. These data indicate that leptin binds the bovine leptin receptor with high affinity and that a pool of leptin is bound to abundant cell membrane-associated proteins. These observations are consistent with the plasma concentration range for leptin and imply that free leptin concentration in the tissues may be partially buffered by cell-associated and bound forms in plasma. Thus, acute changes in leptin secretion may have little effect at the leptin receptor. The development of leptin agonists/antagonists should facilitate further characterization of leptin binding and clarify the role of abundant low affinity binding sites at the leptin axis.

Differential effects of dexamethasone and clenbuterol on rat growth and on beta2-adrenoceptors in lung and skeletal muscle

Beta-adrenergic agonists increase growth rate, but their efficacy is reduced over time as the number of beta2-adrenoceptors in muscle decreases. Dexamethasone increases beta2-adrenoceptor density in many tissues, but this effect has not been reported in skeletal muscle. In this study, male rats were treated daily for 10 d with either clenbuterol (4 mg/kg of feed), dexamethasone (.2 mg/kg BW, s.c.), or clenbuterol plus dexamethasone. Untreated rats served as controls. Dexamethasone caused a marked suppression of growth rate, which resulted in decreased (P < .001) body weight (-29%), carcass weight (-30%), hind-limb muscles (-22%), omental fat (-22%), and heart weight (-10%). Feed intake was reduced (-26%), but feed conversion efficiency was also impaired (P < .001). Clenbuterol caused a small increase in growth rate (+6%; P < .05), with an increase in leg muscle (+7%; P < .01) and heart mass (+8%; P < .05). Feed efficiency was improved (P < .001) by clenbuterol. Rats given the combined treatment still showed a reduction in growth rate (-81%). Clenbuterol caused only a mild attenuation of the effects of dexamethasone on feed intake, BW, and carcass weight, but reduced the catabolic effect of dexamethasone on hind-limb muscle to only -8%. Clenbuterol caused a slight increase in the affinity beta2-adrenoceptors in lung for binding to the radioligand (-)[125I]iodocyanopindolol. Relative to control values, the density of beta2-adrenoceptors in lung was +31% with dexamethasone treatment, -45% with clenbuterol, and -23% with the combined treatment. Clenbuterol also decreased beta2-adrenoceptors in skeletal muscle (-35%), but so did dexamethasone (-13%), so the effects of the beta-adrenergic agonist were not attenuated through use of the combined treatment (-40%). The results show that the inductive effect of glucocorticoids on beta2-adrenoceptors is tissue-specific and that glucocorticoid treatment is not a useful adjunct to beta-adrenergic agonist treatment in animal production.

An interlaboratory measurement of screen-film speed and average gradient according to ISO 9236-1

The speed and average gradient of a conventional screen-film system was measured at four European laboratories. This is the first interlaboratory comparison in which the measurement conditions described in ISO 9236-1 were applied. The four laboratories used calibrated measurement equipment. The values obtained by the four laboratories were within a range of 14% for the speed and within a range of 8% for the average gradient. These variations are consistent with the expected measurement uncertainty.

Reducing metabolic rate by immunoneutralisation of catecholamines

A conjugate of noradrenaline and ovalbumin was used to produce anti-noradrenaline antibodies in goats and Brahman steers. Three weeks after the primary immunisation, anti-noradrenaline binding was detected in the sera of 2 of 5 immunised steers but none was detected in any steers 6 weeks after immunisation. Three weeks after immunisation, immunised steers, including the ones with no detectable anti-noradrenaline antibodies, had a larger change (P < 0.02) in fasting metabolic rate from pretreatment values (–14.5 W) than did paired controls (+3.3 W). After 6 weeks, the changes in fasting metabolic rate for the treated and control groups were –17.8 Wand –36.6 W (P < 0.08), respectively. Anti-noradrenaline polyclonal antibodies purified from goat serum had an approximate dissociation constant for binding to noradrenaline of 4 µM and a specific binding capacity of 178 nM in the immunoglobulin solution prepared, equivalent to about 30 mg/L of anti-catecholamine antibodies in the original goat serum. When 1 mL of this immunoglobulin solution was injected into rats, their metabolic rate was lowered by >10% relative to rats treated with control immunoglobulin solution (P < 0.05). These results demonstrate that the lowering of metabolic rate by an immunological approach which targets control points in the sympathetic nervous system is feasible and could offer an immunologically based method of growth promotion for beef cattle.

Leptin: its pharmacokinetics and tissue distribution

OBJECTIVE

The pharmacokinetics and tissue distribution of leptin in rats was investigated.

DESIGN

A catheter was inserted in the right jugular vein of rats on the day prior to experiment. The next day, blood was sampled and then a tracer dose of radioiodinated hormone was administered via the catheter. Thereafter, small (200 microl) samples of blood were taken at regular intervals. Two experiments were conducted over different sampling times. TCA precipitated radioactivity was counted in samples of plasma and tissues. Pharmacokinetic parameters were calculated after fitting a bi-exponential equation describing a two-pool model of plasma leptin distribution. Selected time-point plasma samples were fractioned using size exclusion chromatography and the leptin distribution determined.

RESULTS

The two pool model described the pharmacokinetics of leptin in two forms: an initial fast decaying pool (t(1/2) = 3.4 min) and a slower decaying pool (t(1/2) = 71 min) with an overall clearance rate of 6.16 ml/min/kg. Size exclusion chromatography showed a persistent peak (all time-points tested) of 125I-leptin corresponding to the plasma albumin peak. The size of the free 125I-leptin peak became diminished or absent in later time-point plasma samples. Tissue distribution of leptin at 60 min and 180 min time-points showed that the small intestine contained the highest concentration of leptin, almost four times the level found in kidneys, liver, stomach and lungs. 125I-leptin was least abundant in skin, muscle, heart, caecum and brain.

CONCLUSION

The pharmacokinetics of leptin are affected by three important factors: 1) its ability to bind to a plasma carrier molecule which increases its half-life; 2) its association with abundant peripheral tissue binding sites which creates an additional pool of leptin and 3) the rate of synthesis of leptin which may be less important than originally believed as the prolonged half-life and the additional pool of tissue binding sites are important factors in determining its plasma concentration.

Effect of corticosterone on beta-adrenoceptor density in rat skeletal muscle

Corticosteroid hormones increase the density of beta-adrenoceptors in some tissues and may be able to prevent the anabolic effects of beta-agonists from becoming attenuated. The aim of this study was to find a suitable dose of corticosterone that would up-regulate beta2-adrenoceptors in skeletal muscle without arresting the animal's growth. Male rats were given five daily injections of corticosterone at 0, 6.25, 12.5, 25, or 50 mg/kg. The animals were far more sensitive to the catabolic effects of this steroid than female rats used in a previous study. There was no change in food intake, liver, heart, or soleus muscle mass, but corticosterone caused a dose-related decrease in weight gain, carcass weight, omental fat pad weight, and gastrocnemius/plantaris muscle mass (P < .01). From a regression of muscle mass against dose, we calculated that 4.4 mg x kg(-1) x d(-1) would be the largest dose of corticosterone that a male rat could tolerate without any catabolic effect in skeletal muscle. Corticosterone failed to increase beta-adrenoceptor density at any of the doses tested. We conclude that corticosterone treatment is unlikely to be effective at enhancing the growth response of male rats to beta-agonists.

The effect of the alpha 2-adrenoceptor agonist, guanfacin, on energy expenditure, intake and deposition in rats

The effect of guanfacin on the energy expenditure, food intake and body composition of female Wistar rats at maintenance was studied. Rats on a restricted food intake (about 75% of ad libitum), treated for 6 days with twice-daily injections of guanfacin.HCl (0.5 mg/kg) showed large reductions in energy expenditure (30%, p < 0.001) compared to control animals but no significant differences in liveweight gain, dry mass gain, or gains in total body energy content, protein, fat and ash. The treated group had a lower intake of metabolizable energy (9%, p = 0.01) partially due to a lower intake of food. However, this lower intake of energy did not fully account for the lowered energy expenditure in the treated animals. The unaccounted lowered energy expenditure was not due to changes in the diurnal pattern of energy expenditure since continuous indirect calorimetry with rats fed ad libitum, over 3 days, showed that twice-daily injections of guanfacin (0.5 mg/kg per injection) achieved a sustained decrease in energy expenditure. The lack of an increased growth rate of rats treated with guanfacin was attributed to behavioural changes; to a decreased food intake and to other, unknown, factors related to energy expenditure.

Effects of alpha-adrenoceptor agonists and antagonists on metabolic rate in cattle

Brahman steers (Bos indicus) were treated with the alpha 2-adrenergic agonists, guanfacin.HCl (4-440 micrograms/kg), UK14304.HCl (20-125 micrograms/kg) and clonidine.HCl (0.2-5 micrograms/kg). All three agonists produced dose-dependent reductions in metabolic rate, heart rate and rectal temperature (P < 0.001). Brahman heifers were infused with idazoxan.HCl (10 micrograms/kg/hr), an alpha 2-adrenergic antagonist, alone and in combination with an intramuscular injection of guanfacin.HCl (80 micrograms/kg). Idazoxan alone did not alter rectal temperature but it blocked the guanfacin-induced lowering of rectal temperature (P = 0.05 for the interaction between the two drugs). Idazoxan alone raised metabolic rate (P = 0.01). Guanfacin lowered metabolic rate (P = 0.007) and heart rate (P = 0.03), but the blocking of the guanfacin effect by idazoxan could not be demonstrated (P > 0.05) for either. The same heifers treated with 0.5, 1.0 and 5 micrograms/kg prazosin.HCl, an alpha 1-adrenergic antagonist, had significant changes in metabolic rate (P = 0.003) and heart rate (P = 0.008) at 0.5 and 5 micrograms/kg. Metabolic rate and heart rate decreased at the lower dose and increased at the higher dose. These results with cattle parallel previous results in rats (Gazzola, 1993) where a minimal, conceptual model for the partial control of resting metabolic rate by the sympathetic nervous system was postulated. The model indicates points of control in the sympathetic nervous system which could be manipulated so as to alter the metabolic rate of farm animals.

Alpha 2-adrenoceptor-mediated effects on resting energy expenditure

The effects of the alpha 2-adrenoceptor agonist guanfacin, other alpha-adrenoceptor agonists, beta-adrenoceptor agonists and alpha- and beta-adrenoceptor antagonists on resting energy expenditure (REE) were studied in female Wistar rats at 23 degrees C. Guanfacin produced a maximum change of -20% (-1.2 W/kg0.75, P < 0.001) in REE in rats with a mean +/- s.d. pre-treatment REE of 6.0 +/- 0.9 W/kg0.75. The dose producing half the maximum effect was 0.4 mg/kg. Other alpha 2-adrenoceptor agonists, clonidine, UK14304 and the peripherally acting alpha 2-agonist, p-aminoclonidine, also decreased REE. The effects of guanfacin were antagonized by idazoxan, yohimbine and RX821002 (all selective for alpha 2-adrenoceptors) but not prazosin (selective for alpha 1-adrenoceptors). Prazosin used alone lowered REE indicating a role for alpha 1-adrenoceptors in normal REE. To determine whether guanfacin was acting directly on oxygen-consuming tissues or if it was acting by lowering sympathetic tone, rats were treated with selective beta 1-, beta 2- and beta 3-agonists and antagonists both alone and in combination with guanfacin. The results of these experiments support the hypothesis that guanfacin lowered REE through a decrease in sympathetic tone (noradrenaline release) which in turn lessened the normal resting stimulation of alpha 1- and beta 1-adrenoceptors.

Effects of guanfacin and nitroprusside on the haemodynamics and oxygen consumption of Brahman steers

1. The systemic vascular resistance (SVR) and oxygen consumption of high grade Brahman (Bos indicus) steers were measured before and after treatment with guanfacin and nitroprusside to test whether the decreased whole-body oxygen consumption seen with guanfacin treatment is due to less oxygen consumption by vascular smooth muscle. 2. Guanfacin changed oxygen consumption by -31% but raised SVR by 61%. Nitroprusside had no significant effect on oxygen consumption but changed SVR by -20%. Moreover, with guanfacin, the changes in oxygen consumption and SVR were temporally incongruent. 3. We conclude that the lowered whole-body oxygen consumption caused by guanfacin was not due to decreased consumption by vascular tissue.

Energy and growth

In this review we explore the relation between energy needs and growth. In the normal animal, we assume there are fixed values for the efficiency with which protein and fat are deposited. However, through modern technology, growth is increasingly being altered, either through the use of hormones, vaccines, or genetic manipulations. By examining the effects of such treatments (including different levels of feeding and the use of protein, steroid and catecholamine growth promoters), on the relation between protein and fat deposition, we attempt to determine how these treatments affect the efficiency of growth. What emerges from this review, is that each type of treatment (and in some cases individual compounds within a class) has a different spectrum of activity with respect to effects on food intake, the efficiency of protein and fat deposition, and the maintenance requirements of the animal. Moreover, the degree of variation in the efficiency with which available energy is used to deposit tissue, particularly protein, is shown to be marked. Whereas the size of this variation suggests that there is considerable scope for further improvements in domestic animal productivity through 'growth engineering', to make this progress, the cause of this variation needs to be better understood. Steps towards this understanding can be made by further studies on the mechanisms of action of available anabolic and catabolic hormones, and on their interactions with the sympathetic nervous system.

Increasing annual growth rates of cattle by reducing maintenance energy requirements

In seasonally dry areas cattle undergo periods of arrested growth because the forage on offer is of poor quality. Annual liveweight gains could be increased and age of turnoff for slaughter reduced if maintenance energy requirements could be lowered during the dry season with no concomitant reduction in forage intake. Strategies to reduce metabolic rate, and so rate of liveweight loss using the anabolic steroid, trenbolone acetate, and the �2-agonist, guanfacin, are discussed. Both compounds reduced fasting metabolic rate of steers; an implant of 300 mg trenbolone acetate by about 10% and continuous intravenous infusion of 40 8g/kg liveweight per day guanfacin by about 20%. The effects of other anabolic steroids on energy metabolism is reviewed. Trenbolone treatment of steers fed a low-protein roughage diet reduced voluntary feed intake. The mechanism by which this occurred was established and is discussed, as are studies aimed at determining the mechanism by which trenbolone reduces metabolic rate. Further, it has been established that the guanfacin-induced reduction in metabolic rate which is largely mediated peripherally is an �2-adrenergic effect and not some other effect of the drug.

Jack bean urease (EC 3.5.1.5). V. On the mechanism of action of urease on urea, formamide, acetamide, N-methylurea, and related compounds

Acetamide and N-methylurea have been shown for the first time to be substrates for jack bean urease. In the enzymatic hydrolysis of urea, formamide, acetamide, and N-methylurea at pH 7.0 and 38 degrees C, kcat has the values 5870, 85, 0.55, and 0.075 s-1, respectively. The urease-catalyzed hydrolysis of all these substrates involves the active-site nickel ion(s). Enzymatic hydrolysis of the following compounds could not be detected: phenyl formate, p-nitroformanilide, trifluoroacetamide, p-nitrophenyl carbamate, thiourea, and O-methylisouronium ion. In the enzymatic hydrolysis of urea, the pH dependence of kcat between pH 3.4 and 7.8 indicates that at least two prototropic forms are active. Enzymatic hydrolysis of urea in the presence of methanol gave no detectable methyl carbamate. A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently an O-bonded carbamato-enzyme intermediate.

Jack bean urease (EC 3.5.1.5). IV. The molecular size and the mechanism of inhibition by hydroxamic acids. Spectrophotometric titration of enzymes with reversible inhibitors

Kinetic, spectral, and other studies establish that hydroxamic acids bind reversibly to active-site nickel ion in jack bean urease. Equilibrium ultracentrifugation studies establish that the molecular weight of native urease is 590 000 +/- 30 000 while that of the subunit formed in 6 M guanidinium chloride in the presence of beta-mercaptoethanol is approximately 95 000. Essentially the same subunit molecular weight (approximately 93 000) is found by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, subsequent to denaturation in a guanidinium chloride - beta-mercaptoethanol system at various temperatures. Coupled with an equivalent weight of 96 600 for binding of the inhibitors acetohydroxamic acid and phosphoramidate, these results establish securely that urease is a hexamer with one active site per 96 600-dalton subunit. Consistent values for the equivalent weight are obtained by a routine spectrophotometric titration of the active site of freshly prepared urease with trans-cinnamoylhydroxamic acid. General equations are derived which describe spectrophotometric titrations of binding sites of any enzyme with a reversible inhibitor. These equations allow the evaluation of the difference spectrum of the protein-inhibitor complex even when the binding sites cannot readily be saturated with the inhibitor or vice versa.

Jack been urease (EC 3.5.1.5). II. The relationship between nickel, enzymatic activity, and the "abnormal" ultraviolet spectrum. The nickel content of jack beans

At low pH, EDTA promotes the loss of the tightly bound nickel ions from jack bean urease. The specific activity of soluble enzyme after partial EDTA-promoted inactivation is a linear function of the nickel content. The results are consistent with the presence of 2.0 nickel ions per 97 000-dalton subunit in pure urease. The time scale for loss of enzymatic activity and nickel under these conditions is similar to that for loss of the "abnormal" tail absorption in the ultraviolet and visible absorption spectrum of urease (including the shoulder at approximately 420 nm). This indicates that nickel in urease is essential for enzymatic activity and establishes that the metal ions are in part responsible for the tail absorption in the ultraviolet spectrum of urease. After partial inactivation in the presence of EDTA either at low pH or in 2.5 M guanidinium chloride at neutral pH, urease did not regain activity in the presence of Ni2+. As yet apourease has not been produced reversibly. Jack bean seeds grown hydroponically without added nickel were low in both urease activity and nickel (10 and 6%, respectively, of parent seeds). Several other metal ions were readily available. This result suggests that metal ions other than nickel cannot substitute for nickel in the formation of normally active urease.

Metal ions in enzymes using ammonia or amides

In an attempt to understand the role of nickel in jack bean urease (1), we turned to a variety of other enzymes important in the utilization, production, or transfer of ammonia. We found several, including the L-histidine and L-phenylalanine ammonialyases and some enzymes that utilize glutamine or ammonia in amidotransferase reactions, all of which show evidence for the involvement of as yet unreported transition metal ions in their mechanism of action. We support the view that catalysis by metalloenzymes may be a reflection of the chemistry of the metal ion itself as a Lewis acid, and that perhaps too much emphasis has been placed on supposed special characteristics (such as strains, "entasis") of the enzyme-metal ion association. In this context, we have discussed the mechanism of catalysis of hydrolysis of specific substrates by carboxypeptidase A, and have returned to urease to examine the role of nickel in its mechanism of action.

On the substrate specificity of jack bean urease (urea amidohydrolase, EC 3.5.1.5)

pH-Stat studies prove that N-methylurea, ethyl carbamate, and carbamoyl azide are not substrates for jack bean urease. Semicarbazide is a good substrate, showing Michaelis–Menten kinetics and stoichiometric formation of ammonia, carbonic acid, and hydrazine, and having a kcat of about [Formula: see text] that of urea at pH 7.