Expanded materials from quartz-porphyrite sands

Experiments on the preparation of glass from quartz-porphyrite sands showed the occurrence at about 1300° C of extensive bubble formation which cannot be easily removed on further heating at higher temperatures. This prompted us to exploit this process in the synthesis of expanded material. The research work was addressed to determining the origin of the bubble phenomenon in order to control the potential foaming at high temperature. The parameters controlling the production of cellular glass directly from quartz-porphyrite sands are presented and discussed. The results allow the preparation of polycellular vitreous material with a homogenous bulk distribution of SiO₂ microcrystals. The main features of the product are: bulk density in the range 720 to 980 kg m^–3; average bubble diameter 0.1 to 0.3 mm; thermal conductivity 0.19 to 0.28 Wm^–1 (°C)^–1; compressive strength 1.96 to 3.92 M Pa.     

A high-resolution digital time-interval measurement instrument

A new method for time-interval measurements is described and the results of measurements on a prototype are given. This method uses a virtually periodic exponential signal as the reference clock and consists of measuring both the phase deviation and the number of cycles of this clock signal between the beginning and the end of the unknown time-interval. The use of two auxiliary sinusoidal signals in order to measure the phase of the corresponding periodic exponential signal is discussed, also considering the main causes of error. The functional block diagram of the prototype is described in detail and the measurement results show that a resolution improvement of two orders of magnitude with respect to the period of the clock signal can easily be obtained.     

<Emphasis Type="Italic">In vivo</Emphasis> measurement of the redox state

As part of an aerobic life, we oxidize a large pool of biomolecules to obtain chemical energy. During this process, several intermediates are formed; some are chemically unstable and are referred to as free radicals (FR). FR tend to react quickly with their surrounding biological environment; depending on the nature of the molecule attacked, different reactions can occur, i.e., lipid peroxidation, protein oxidation, or DNA oxidation products. As aerobic life has evolved, antioxidant defense systems against FR have developed. When an imbalance between production of FR (oxidants) and defese systems against them (antioxidants) happens, a situation of oxidative stress occurs. This can lead to irreversible biochemical changes, with subsequent tissue damage and disease. Establishing the involvement of FR in the pathogenesis of a disease has been difficult because of the lack of sensitie and specific methodology to detect them. No ideal biomarkers for in vivo FR-induced damage are available as yet. However, some reliable indices of FR formation are now available, and in some pathologic conditions, evidence is accumulating to show that FR damage might play a functional role. The task for the near future will be to try to simplify the analytical methodology and elucidate the molecular mechanisms underlying the formation, disposition, and kinetics of FR marker molecules.     

An analytical study of strategy-oriented restructuring algorithms

Considerable experimental evidence has been accumulated showing that the performance of programs in virtual memory environments can be significantly improved by restructuring the programs, i.e., by modifying their block-to-page or block-to-segment mapping. This evidence also points out that the so-called strategy-oriented algorithms, which base their decisions on the knowledge of the memory management strategy under which the program will run, are more efficient than those algorithms which do not take this strategy into account.We present here some theoretical arguments to explain why strategy-oriented algorithms perform better than other program restructuring algorithms and determine the conditions under with these algorithms are optimum. In particular, we prove that the algorithms oriented towards the working set or sampled working set policy are optimum when applied to programs having no more than two blocks per page, and that, when this restriction is removed, they minimize both upper and lower bounds of the performance index they consider as the figure of merit to be reduced. We also prove that the restructuring algorithms aimed at reducing the page fault rate of programs to be run under such policies as LRU, Global LRU and PFF (the Page Fault Frequency policy) minimize an upper bound of the page fault rate, and we extend some of our results to some non-strategy-oriented algorithms. Throughout the paper, the only assumption about program behavior is that it can be accurately modeled as a stationary discrete-state stochastic process.     

Dynamic management of guaranteed-performance multimedia connections

Most of the solutions proposed to support real-time (i.e., guaranteed performance) communication services in packet-switching networks adopt a connection-oriented and reservation-oriented approach. In such an approach, resource allocation and route-selection decisions are made before the start of the communication on the basis of resource availability and real-time network load at that time, and are usually kept for the duration of the communication. This ratherstatic resource-management approach has certain limitations. It does not take into account (a) the dynamics of the communicating clients; (b) the dynamics of the network state; and (c) the tradeoff between quality of service and network availability, thus affecting theavailability andflexibility of the real-time network services. Availability is the ability of the network to accommodate as many real-time clients as possible, while flexibility is the ability to adapt the real-time services to the changing state of the network and the client demands. In this paper, we present the dynamic connection management (DCM) scheme, which addresses these issues by providing the network with the capability of dynamically modifying the performance parameters and the routes of any existing real-time connection. With this capability, DCM can be used to increase the availability and flexibility of the guaranteed-performance service offered to the clients.     

The detection of residual pectin methylesterase activity in pasteurized tomato juices

The enzyme pectin methylesterase (PME) is believed to be involved in the destabilization and cloud loss of vegetable juices through the de-esterification of pectin followed by the successive coprecipitation of the pectate with insoluble materials present in the juices. Cloud destabilization is often observed even when the vegetable products have been subjected to thermal treatment to produce sterile products and also to stabilize the cloud. Therefore it is possible that loss of cloud may be because of residual enzymatic activities surviving the thermal treatments. However, so far no evidence demonstrating the existence of residual PME activity in pasteurized juices has been published. In this paper it is reported that in industrial tomato products showing cloud loss residual PME activity is present. It has been possible to detect this very low activity by an affinity chromatography procedure. The method is based on a cyanogen bromide-activated resin which is coupled with a pectin methylesterase inhibitor protein purified from kiwi fruit. This resin binds native PME with high selectivity and the enzyme can be concentrated from the product in a single step. Thus, the very low PME residual activity present in pasteurized juice and generally not detectable with common techniques can be detected and easily determined with the method described in this paper.     

Stress triaxiality effect on void nucleation in ductile metals

The stress triaxiality effect on the strain required for void nucleation by particle‐matrix debonding has been investigated by means of micromechanical modelling. A unit‐cell model considering an elastic spherical particle embedded in an elastic‐plastic matrix was developed to the purpose. Particle‐matrix decohesion was simulated through the progressive failure of a cohesive interface. It has been shown that the parameters of matrix‐particle cohesive interface are correlated with macroscopic material properties. Here, a simple relationship for the maximum cohesive opening at interface failure as a function of material fracture toughness and yield stress has been derived. Results seem to confirm that, increasing stress triaxiality, the strain at which void nucleation is predicted to occur decreases exponentially in a similar way as for fracture strain. This result has substantial implications in modelling of ductile damage because it indicates that if the stress triaxiality is high enough, ductile fracture can occur at plastic strain lower than that necessary to nucleate damage for moderate or low stress triaxiality regime.     

Design,Synthesis, and Biological Evaluation of Tetrahydro‐β‐carboline Derivatives as Selective Sub‐Nanomolar Gelatinase Inhibitors

Targeting matrix metalloproteinases (MMPs) is a pursued strategy for treating several pathological conditions, such as multiple sclerosis and cancer. Herein, a series of novel tetrahydro‐β‐carboline derivatives with outstanding inhibitory activity toward MMPs are present. In particular, compounds 9 f , 9 g , 9 h and 9 i show sub‐nanomolar IC₅₀ values. Interestingly, compounds 9 g and 9 i also provide remarkable selectivity toward gelatinases; IC₅₀=0.15 nm for both toward MMP‐2 and IC₅₀=0.63 and 0.58 nm , respectively, toward MMP‐9. Molecular docking simulations, performed by employing quantum mechanics based partial charges, shed light on the rationale behind binding involving specific interactions with key residues of S1′ and S3′ domains. Taken together, these studies indicate that tetrahydro‐β‐carboline represents a promising scaffold for the design of novel inhibitors able to target MMPs and selectively bias gelatinases, over the desirable range of the pharmacokinetics spectrum.     

The role of mass spectrometry in the study of non-enzymatic protein glycation in diabetes: an update

Recent studies on non-enzymatic protein glycation are reviewed, and results are critically discussed. Advanced glycation end products (AGE) levels in the body reflect a balance between their formation and catabolism. AGE proteolysis leads to the formation of low-molecular-weight AGE (AGE peptides) that are normally excreted in urine. In the case of diabetic disease and/or renal failure, AGE peptides accumulate in plasma. Because of their high reactivity, these compounds have been thought to play a role in the progression of chronic complications. The structural identification of these compounds is particularly important, and a strategy has been designed for their possible definition. A series of experiments has been devoted to the study of the enzymatic degradation products of in vitro glycated human serum albumin (HSA). This approach, based on different MS methods (LC/ESI/MS, LC/ESI/FTMS, MALDI), led to the detection of the glycated peptides generated by digestion of HSA. A further study was devoted to the possible identification of the peptides identified in the glycated HSA digestion products in the plasma of diabetic and nephropatic subjects. No glycated HSA digestion products were found in plasma samples of the subjects under investigation even if clear differences were found among the LC runs from populations of healthy, diabetic, and nephropatic subjects. Parallel investigations were devoted to the evaluation of glyoxal and methylglyoxal-dicarbonyl compounds that originate at the intermediate stage of the Maillard reaction. This evaluation was performed in diabetic patients, before and after the achievement of good metabolic control, and in nephropatic patients subjected to peritoneal dialysis (PD). In the latter case, results indicated that these dicarbonyl compounds, already present in the dialysis fluids, show a decrease in plasma and in dialysis fluids; those data suggested their reaction at peritoneal membrane level.     

Wetting behavior of graphite and CFC composites by Cu-Ti compacts

The wetting behavior of Cu-Ti powder compacts with 22 wt %Ti and 50 wt %Ti on carbon materials, including graphite and carbon fiber reinforced carbon composites(CFC), has been investigated in a vacuum using the sessile drop method. The equilibrium contact angles of Cu-22Ti(containing 22 wt%Ti) on the graphite and the CFC substrates at 1 253 K are 32 o and 26 o, respectively, whereas the equilibrium contact angle of 9° is obtained for Cu-50Ti(containing 50 wt%Ti) on both the graphite and the CFC substrates at 1 303 K.Microstructural analysis of the wetting samples shows that a thin TiC reaction layer is developed at the interfacial area and Ti-Cu intermetallic compounds are formed over the reaction layer. The investigation on the spreading kinetics of Cu-Ti compacts on carbon materials substrates at fixed temperatures reveals that the spreading is controlled by the interfacial reactions in the first stage and then by the diffusion of the active Ti from the drop bulk to the triple line in the later stage. The spreading is promoted by the intense reaction at higher Ti concentrations.