Effect of polymorphic phase transformations in Al2O3 film on oxidation kinetics of aluminum powders

Thermogravimetry was used to study the oxidation of aluminum powders at elevated temperatures. Aluminum powders of various particle sizes and surface morphologies were heated in oxygen up to 1500 °C at different heating rates. Partially oxidized samples were recovered from selected intermediate temperatures and the oxide phases present were analyzed by X-ray diffraction. The experimental data were related to current information on stabilities and phase changes of Al₂O₃ polymorphs. Aluminum powders were observed to oxidize in four distinct stages in the temperature range from 300 to 1500 °C. During stage I, from 300 to about 550 °C, the thickness of the natural amorphous alumina layer on the particle surface increases. The rate of this process is controlled by the outward diffusion of Al cations. At about 550 °C, when the oxide layer thickness exceeds the critical thickness of amorphous alumina of about 4 nm, the oxide transforms into γ-Al₂O₃. The specific volume of γ-Al₂O₃ is less than that of amorphous alumina; therefore, the newly formed γ-Al₂O₃ only partially covers the aluminum surface. The oxidation rate increases rapidly at the onset of stage II, but it decreases when the γ-Al₂O₃ layer becomes continuous. During stage III oxidation, the γ-Al₂O₃ layer grows and partially transforms into the structurally similar θ-Al₂O₃ polymorph. Finally, oxidation stage IV is observed after the transition to stable -Al₂O₃ results in an abrupt reduction of oxidation rate. Qualitative analysis of the rates of oxidation at the different stages enables one to understand the wide range of aluminum ignition temperatures observed for particles of different sizes.     

On Adaptive Density Deployment to Mitigate the Sink-Hole Problem in Mobile Sensor Networks

The use of mobile sensors is of great relevance to monitor critical areas where sensors cannot be deployed manually. The presence of data collector sinks causes increased energy depletion in their proximity, due to the higher relay load under multi-hop communication schemes (sink-hole phenomenon). We propose a new approach towards the solution of this problem by means of an autonomous deployment algorithm that guarantees the adaptation of the sensor density to the sink proximity and enables their selective activation. The proposed algorithm also permits a fault tolerant and self-healing deployment, and allows the realization of an integrated solution for deployment, dynamic relocation and selective sensor activation. We formally prove the termination of our algorithm. Performance comparisons between our proposal and previous approaches show how the former can efficiently reach a deployment at the desired variable density with moderate energy consumption under a wide range of operative settings.     

Surgical reinstatement of aesthetics in the maxillary anterior region: a case report

The maxillary anterior region is frequently treated for aesthetic enhancement. This article presents the case of a patient who had undergone surgery for treatment of a tumor of the hypophysis involving intraoral access to the sella turcica. The treatment had caused the formation of severe gingival recession on the buccal surface of the maxillary anterior teeth. A variety of surgical techniques were considered for covering the exposed root surfaces. The surgical site was analyzed, and the response of the periodontal tissue to the treatment was anticipated. The bilaminar method, utilizing a subpedicle connective tissue graft (SCTG), was selected. The learning objective of this case presentation is to demonstrate that when the appropriate treatment procedure is selected, restoration of function and aesthetics can be achieved even in the most advanced cases.     

Helping by unambiguous computation and probabilistic computation

Schöning [S] introduced a notion of helping and suggested the study of the class P_help(C) of languages that can be helped by oracles in a given classC. He showed that P_help(BPP) is included in ZPP. Later, Ko [K] introduced a weaker notion of helping, called one-sided helping, and proved that P_1-help(BPP) is included in R and that UP is included in P_1-help(UP). The three inverse inclusions are open problems (see [Hem]). Caiet al. [CHV] constructed a relativized world in which the third open inclusion fails. We show relativized worlds in which all three open inclusions fail in a strong way. In particular, we strengthen the result of Caiet al., showing that P_help(UP) is not included in Few. This is obtained as a corollary of a general result that gives sufficient conditions, on a relativizable complexity classC, to ensure the relativized separation of P_help(UP) fromC. Further separations are also derived. The other two open inclusions are showed to fail strongly by the relativized separation of ZPP from P_1-help(AM ∩ co-AM).     

Hepatitis C virus infection among cryoglobulinemic and non-cryoglobulinemic B-cell non-Hodgkin's lymphomas

BACKGROUND AND OBJECTIVE: Since hepatitis C virus (HCV) infection has been associated with different histotypes of B-cell non-Hodgkin's lymphoma (NHL), with or without concomitant production of cryoglobulins (cryolg), we have investigated the prevalence of the infection among NHL with the aim of defining its relationship with the histotype and with the production of cryolg. METHODS: Four-hundred and seventy unselected, consecutive patients with a diagnosis of B-cell NHL were investigated. Anti-HCV antibodies (Ab) and cryolg were sought in all while HCV RNA and rheumatoid factor were detected on HCV-Ab positive samples. RESULTS: Overall, the prevalence of HCV infection was 8.9% (42/470). It was 95.4% (#21) among the 22 patients with, and 4.6% (#21) among the 448 without production of cryoIg. The most common histotype among the HCV-positive, cryoIg-producing cases, was the immunocytoma (16/21, 76%). Among the HCV-positive, non cryoIg-producing cases, the marginal zone and the follicle center lymphomas were the commonest. INTERPRETATION AND CONCLUSIONS: Close association between HCV infection and cryoIg production, already described in mixed cryoglobulinemia, is confirmed also among B-cell NHL. Nevertheless, 50% of HCV-related lymphomas are non-cryoIg producers. Low-grade lymphomas (in particular the immunocytoma) are the most frequent HCV-related lymphomas. Since new therapeutic strategies might be necessary if the virus is detected, screening for cryoIg and for HCV-Ab among B-cell NHL at diagnosis is mandatory.     

Responses of preterm infants to unimodal and multimodal sensory intervention

PURPOSE: To examine the immediate responses of preterm infants to two forms of unimodal [auditory only (A) and tactile only (T)] and two forms of multimodal sensory stimulation [auditory, tactile and visual (ATV); auditory, tactile, visual and vestibular (ATVV)]. METHOD: A convenience sample of 54 clinically stable preterm infants (33-34 postconceptional weeks) was randomly assigned to 1 of 5 experimental groups [Control (C); (A); (T); (ATV); and (ATVV)]. Stimulation was applied for 15 minutes once daily for 4 consecutive days. RESULTS: Outcome measures included pulse (PR) and respiratory rate (RR), oxygen saturation, behavioral state (BS), and body temperature. Repeated measures ANOVA identified significant differences among the groups during intervention for PR (p < .001), RR (p = .01), and BS (p < .02). Infants receiving any intervention with a tactile component showed increasing arousal (change in BS), and increased PR and RR during stimulation. Group T infants had higher proportions of PR > 180 while Group ATVV had higher proportions of PR < 140 (p = .0001). Group ATVV showed increased alertness following stimulation (24%) in contrast to having the least alertness during stimulation (11%). CONCLUSIONS: Tactile stimulation alone may be too arousing for these infants while the addition of vestibular stimulation may modulate arousal and facilitate optimal arousal prior to feeding.     

T-cell receptor V beta-specific expansions in children from HIV-infected mothers

This paper present a tonometer incorporated in a contact lens, which allows simultaneous measurement of intraocular pressure and performance ophthalmoscopy. The tonometer can record the pulse curve continuously, which can give us an indication of any circulatory problem. The device is therefore expected to yield additional information useful for the diagnosis of early glaucoma. Te device has three force sensors built in, which allow continuous measurement of the force exerted on the eye surface by the contact lens. The force of the contact lens on the eye can be altered and makes the adjustment of different eye pressures possible. These induced changes of the eye pressure and their influence on the fundus can be checked. We have taken some measurements on enucleated human eyes to compare our device with a Statham tansducer in the vitreous. We found a good correlation. We are currently taking measurements in volunteers. The clinical relevance of these observations and measurements will be examined in a future study.     

An application of limited branching in clustering

The technique of limited branching is used to answer an open problem of P. Brucker (1977) arising in a study of computational complexity of clustering problems. This problem is shown to be solvable by a polynomial algorithm.