Policy hierarchies for distributed systems management

Distributed system management, involves monitoring the activity of a system, making management decisions and performing control actions to modify the behavior of the system. Most of the research on management has concentrated on management mechanisms related to network management or operating systems. However, in order to automate the management of very large distributed systems, it is necessary to be able to represent and manipulate management policy within the system. These objectives are typically set out in the form of general policies which require detailed interpretation by the system managers. The paper explores the refinement of general high-level policies into a number of more specific policies to form a policy hierarchy in which each policy in the hierarchy represents, to its maker, his plans to meet his objectives and, to its subject, the objectives which he must plan to meet. Management action policies are introduced, and the distinction between imperatival and authority policies is made. The relationship of hierarchies of imperatival policies to responsibility, and to authority policies, is discussed. An outline approach to the provision of automated support for the analysis of policy hierarchies is provided, by means of a more formal definition of policy hierarchy refinement relationships in Prolog     

Autoradiographic assessment of blood flow heterogeneity in the hamster heart

OBJECTIVE: Provide regional flow measurement in the hearts of small mammals using a new, higher-resolution technique based on the deposition of a molecular marker. METHODS: We determined the instantaneous extraction and retention of the "molecular microsphere" radiolabeled desmethylimipramine in retrogradely perfused hamster hearts. In a separate series of experiments, autoradiography was used to measure regional myocardial deposition densities in hamster hearts of about 0.5 g with spatial area resolution of 16 x 16 microns. RESULTS: Radiolabeled desmethylimipramine is almost 100% extracted during a single transcapillary passage and is retained in the tissue for many minutes. Autoradiographic images demonstrated a spatial flow heterogeneity with standard deviations of 31 +/- 4% of the mean flow (N = 5) in 16 x 16 x 20-micronm3 voxels. This is equivalent to the projections made using fractal relationships from cruder observations obtained with microspheres in the hearts of baboons, sheep, and rabbits. CONCLUSIONS: Autoradiography using a molecular deposition marker provides quantitative information on myocardial flow heterogeneities with resolution at the size of cardiac myocytes. Because the regions resolved are smaller than the volume of regions supplied by single arterioles, the results must slightly exaggerate the true heterogeneity of regional flows.     

A piezoelectric, flexural-disk, neutrally buoyant, underwater accelerometer

A piezoelectric, flexural-disk accelerometer for underwater use is composed of two PZT-5A lead zirconate-titanate disks that are bonded to an aluminum substrate. The substrate is edge-supported inside an aluminum housing. The housing is enclosed in syntactic foam so that the sensor is neutrally buoyant. The overall height is 1.0 in. (26 mm), the overall diameter is 1.9 in. (49 mm), and the total mass is 0.054 kg. With 25 ft (7.6 m) of (230 pF/m) cable attached, the sensitivity is -42 dB re 1 V-s(2)/m (-22 dB re 1 V/g), the capacitance is 5.0 nF, and the resonance frequency is 11 kHz. When used in conjuction with a Micro Networks MN3210 preamplifier, the spectral noise-equivalent acceleration floor is approximately -171 dB re 1 m/s(2)- radicalHz (-151 dB re 1 g/ radicalHz) at 5 kHz.     

Real-time determination of picomolar free Cu(II) in seawater using a fluorescence-based fiber optic biosensor

We report real-time, in situ determination of free copper ion at picomolar levels in seawater using a fluorescence-based fiber optic biosensor. The sensor transducer is a protein molecule, site-specifically labeled with a fluorophore that is attached to the distal end of an optical fiber, which binds free Cu(II) with high affinity and selectivity. The transducer reports the metal's concentration as a change in fluorescence intensity or lifetime, using a frequency domain approach. The transducer's response time is diffusion-limited, with a typical measurement requiring 30 s. The sensor demonstrates a detection limit of 0.1 pM free Cu(II) in a seawater model. Accuracy and precision of the sensor were at least comparable to cathodic ligand exchange/adsorptive cathodic stripping voltammetry. Measurements of tidal flushing of a copper-contaminated inlet are shown.     

Palmitoylated cysteine 341 modulates phosphorylation of the beta2-adrenergic receptor by the cAMP-dependent protein kinase

We previously showed that substitution of a glycine residue for the palmitoylated cysteine 341 of the human beta2-adrenergic receptor (Gly341beta2AR), increases the basal level of the receptor phosphorylation and reduces its ability to functionally interact with Gs. In the present study, we show that additional mutation of serines 345 and 346 (Ala345,346Gly341beta2AR) restored normal phosphorylation and receptor-Gs coupling, thus suggesting that the increased phosphorylation of this site, rather than the lack of palmitoylation per se, is responsible for the poor coupling of the unpalmitoylated receptor. This is supported by the observation that chemical depalmitoylation of purified beta2AR did not affect the ability of the receptor to stimulate adenylyl cyclase in reconstitution assays. Furthermore, mutation of Ser345,346 in a wild type receptor background (Ala345,346beta2AR) significantly decreased the rate of agonist-promoted desensitization of the receptor-stimulated adenylyl cyclase activity, supporting a role for this phosphorylation site in regulating the functional coupling of the receptor. Since serines 345 and 346 are located in a putative cyclic AMP-dependent protein kinase (PKA) phosphorylation site immediately downstream of the palmitoylated cysteine 341, the hypothesis that the accessibility of this site may be regulated by the receptor palmitoylation state was further assessed in vitro. In membrane phosphorylation assays, Gly341beta2AR was found to be a better substrate for PKA than the wild type receptor, thus supporting the notion that palmitoylation restrains access of the phosphorylation site to the enzyme. Taken together, the data demonstrate that palmitoylation of cysteine 341 controls the phosphorylation state of the PKA site located in the carboxyl tail of the beta2AR and by doing so modulates the responsiveness of the receptor.     

The effect ofn-decanol on solubilization of water-in-oil microemulsions and stability of lamellar liquid crystals of alkylphenol ethoxylates

Addition of n-decanol at appropriate concentrations is beneficial to increasing the solubilization amount of water in a water-in-oil microemulsion in the system of nonylphenol ethoxylate/olive oil/water, but it destabilized the lamellar liquid crystal and reduced the solubilization of olive oil in the lamellar liquid crystal.     

NMR studies on the conformation of the CD4 36-59 peptide bound to HIV-1 gp120

A peptide containing residues 36-59 of the human CD4 receptor includes most of the residues thought to be involved in binding the HIV surface glycoprotein, gp120. This peptide was synthesized and inhibited the binding of gp120 to soluble CD4. NMR relaxation experiments indicated that the peptide was in fast exchange between the free and gp120-bound states. Transferred NOESY NMR showed a number of long-range NOEs, from the gp120-bound state, between residues 38, 40, 45, 48, and 49 of the peptide. NMR evidence also suggested that the Phe43 in the peptide, which corresponds to a critical residue in CD4 for the binding of gp120, makes intimate contact with gp120. The Tr-NOESY cross-peak intensities provided proton-proton distance constraints on the conformation of the gp120-bound peptide. The distance constraints were used in simulated annealing, and a set of 20 very similar structures was obtained for the central region of the gp120-bound peptide. Residues 42-49 of the peptide formed a loop with the side chain of Phe43 pointing away from the rest of the peptide. This Phe43 ring points away from the protein surface in two structures of the amino-terminal domain of CD4 found by X-ray crystallography. Differences in the conformation of CD4 in the two crystal forms suggest that the 36-59 region might be flexible. The NMR data on the 36-59 CD4 peptide predicts a gp120-bound conformation different from either of the CD4 crystal forms in the absence of gp120.     

Processes controlling the thermal regime of saltmarsh channel beds

Spatially and temporally continuous temperature measurements were collected over 32 h using a fiber-optic distributed temperature sensing (DTS) system deployed along 330 m of two intertidal saltmarsh channel beds in northern California. Measured temperature gradients imparted ecosystem-scale structure to the saltmarsh tidal channel thermal regime, which was punctuated by potential warm and cold refugia. Anomalous bed temperatures of 2-4 degrees C occurred throughout the 1.3 tidal cycles at some locations. Discrete locations of consistently warm temperatures characterized sustained seepage of recently infiltrated tidal waters. Low-variance temperature anomalies were typically collocated with hidden microtopographic tributaries that facilitated mixing of warm surface waters and cold groundwater. Bed temperature gradients (approximately 2 degrees C/100 m, average) decreased from high temperatures similar to bay water at the channel mouths to low inland temperatures comparable to groundwater. The trends were maintained by cold groundwater discharge throughout the channels, which affected bed temperatures in proportion to channel reach exposure time; the opposing effect, conductive bed-warming by tidal waters, was proportional to flood duration. DTS is a promising tool for identifying spatial and temporal temperature patterns of hydroecological importance amidst complex natural systems.     

Comparison of copper speciation in coastal marine waters measured using analytical voltammetry and diffusion gradient in thin-film techniques

The diffusion gradient in thin-film hydrogel (DGT) probe is a promising tool for metal speciation work. Based on a passive sampling principle, it provides the potential for large data sets in complex regimes. DGT probes were deployed in waters characterized independently using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV). The CLE-ACSV used benzoyl acetone as the competitive ligand in discrete water samples collected during the deployment of the DGT probes. The DGT probes used a 15% polyacrylamide/0.4% bis-acrylamide cross-linker hydrogel and a Na-form of Chelex-100 to complex metal that fluxed into the probe through the hydrogel. Probes were deployed in locations characterized by the degree of pollution impact: the relatively pristine Vineyard Sound, MA, [Cu]total approximately 6 nM, small seasonally active harbors on Cape Cod, MA, [Cu]total = 12-64 nM, as well as a large polluted estuary, the Elizabeth River, VA, [Cu]total = 44-58 nM, and a large polluted port, San Diego Harbor, CA, [Cu]total = 23-103 nM. This is the first study where DGT probes have been compared with an independent speciation technique in marine systems and used to establish the diffusion coefficient of Cu-complexing ligands in situ. Results showed that the probes produced highly precise data sets, with substantial differences in copper accumulation between contaminated and pristine waters. Comparison of DGT results with CLE-CSV indicate that at least 10-35% of the organically complexed copper derived by CLE-ACSV measurements was DGT-labile. Diffusion coefficients (corrected to 25 degrees C) of organically complexed DGT-labile Cu through the hydrogel ranged from 0.77 x 10(-6) cm2 s(-1) in Vineyard Sound to 2.16 x 10(-6) cm2 s(-1) in the Elizabeth River estuary. Accumulation rates of copper were substantially higher in contaminated waters than in pristine waters, suggesting that the probes in their current form may be useful as tracking tools to detect episodic sources of contamination.     

Antibodies to quinolinic acid and the determination of its cellular distribution within the rat immune system

Antibodies to quinolinic acid were produced in rabbits with protein-conjugated and gold particle-adsorbed quinolinic acid. Quinolinic acid immunoreactivity was below detection limits in carbodiimide-fixed rat brain. In contrast, strong quinolinic acid immunoreactivity was observed in spleen cells with variable, complex morphology located predominantly in the periarterial lymphocyte sheaths. In the thymus, quinolinic acid immunoreactivity was observed in cells with variable morphology, located almost exclusively in the medulla. Lymph nodes and gut-associated lymphoid tissue contained many, strongly stained cells of similar complex morphology in perifollicular areas. Immunoreactivity in liver and lung was restricted to widely scattered, perivascular cells and alveolar cells respectively. Additional stained cells with complex morphology were observed in bronchus-associated lymphoid tissue, in skin, and in the lamina propria of intestinal villi. Follicles in all secondary lymphoid organs were diffusely stained, ranging from mildly to moderately immunoreactive in spleen, to intensely immunoreactive in gut-associated lymphoid tissue. These results suggest that quinolinic acid is an immune system-specific molecule. Two hypothetical schemes are proposed to account for high levels of quinolinic acid in specific cells of the immune system.