Voids in Materials: Adding Functionality during Additive Manufacturing

An often overlooked implication of controlling materials at ever smaller length scales is the control of the inevitable void spaces contained in those materials and components. This miniaturization is widespread and at these small length scales, properties become size dependent, trending toward more ideal material properties. This is corroborated by the extensive selection dispersed phases such as nanotubes and nanometer-scale particles that are available. The technique of additive manufacturing is gaining enormous attention as it offers the ability to make multifunctional components that cannot be made by traditional processing routes. In additive manufacturing, more precise control of material placement presents a unique opportunity to build functionality by the simultaneous control of solid material and voids at multiple length scales. We present an overview of the functionality of voids from the atomic to the millimeter scale, highlighting the current research involving the introduction of voids in additive manufacturing and present future opportunities to incorporate voids by specific additive manufacturing techniques to add functionality

Coated glass microballoons and syntactic foams thereof for environmental cleanup

Titania is of great interest to water purification applications mainly because of its nontoxic nature and its photocatalytic properties. In the presence of ultraviolet (UV) radiation (with energy equal to or greater than its band gap (EG = 3.02 eV) which translates to a wavelength less than or equal to 400 nm) titania exhibits semiconducting properties and creates electron-hole pairs. These electrons and holes give rise to ions, particularly hydroxyl radicals and various superoxides that can be useful in cleaning up a range of organic compounds in their liquid and gaseous phases. We have developed titania coated glass microballoons (GMBs) with high surface area. These hollow GMBs are made of borosilicate glass, have a density of 0.39 g/cm3, and an average diameter of 47µm. The objective is to use syntactic foams made of titania coated GMBs for water purification. This materials system is of great interest because it has the potential of a practical material with broad implications for improving the quality and quantity of drinking water. In this work, we describe the processing by sol-gel of titania-coated glass microballoons (GMBs), followed by making a functional foam for environmental applications by sintering. We will highlight the processing of coated GMBs starting with titanium isopropoxide precursor, the microstructure of the coated GMBs, and some critical materials related issues in environmental cleanup applications

High temperature carrier controlled ferromagnetism in alkali doped ZnO nanorods

Recent efforts in developing spintronic and magneto-optoelectric material for applications have relied on the use of magnetic semiconductors doped with transition metals and have met with limited success. Using a fresh synthesis approach using alkali ions we demonstrate that alkali doped zinc oxide can provide high temperature magnetic semiconductors. We report studies on nanocrystalline powder and pellets of p-type ZnO:Li and ZnO:Na that exhibit ferromagnetism up to 554 K. The ferromagnetic behavior was confirmed from magnetic hysteresis, ferromagnetic resonance, magnetic force microscopy, and explained by a model where substitutional Li+/Na+ in cation site induce local magnetic moments on oxygen atoms. Optimum dopant concentrations enable ferromagnetic exchange interaction leading to high Curie temperature

Bacterial ‘Cell’ Phones: Do cell phones carry potential pathogens?

Cell phones are important companions for professionals especially health care workers (HCWs) for better communication in hospital. The present study compared the nature of the growth of potentially pathogenic bacterial flora on cell phones in hospital and community. 75% cell phones from both the categories grew at least one potentially pathogenic organism. Cell phones from HCWs grew significantly more potential pathogens like MRSA (20%), Acinetobacter species (5%), Pseudomonas species (2.5%) as compared to the non HCWs. 97.5% HCWs use their cell phone in the hospital, 57.5% never cleaned their cell phone and 20% admitted that they did not wash their hands before or after attending patients, although majority (77.5%) knows that cell phones can have harmful colonization and act as vector for nosocomial infections. It is recommended, therefore, that cell phones in the hospital should be regularly decontaminated. Moreover, utmost emphasis needs to be paid to hand washing practices among HCWs

Influence of Personal Preferences on Link Dynamics in Social Networks

We study a unique network dataset including periodic surveys and electronic logs of dyadic contacts via smartphones. The participants were a sample of freshmen entering university in the Fall 2011. Their opinions on a variety of political and social issues and lists of activities on campus were regularly recorded at the beginning and end of each semester for the first three years of study. We identify a behavioral network defined by call and text data, and a cognitive network based on friendship nominations in ego-network surveys. Both networks are limited to study participants. Since a wide range of attributes on each node were collected in self-reports, we refer to these networks as attribute-rich networks. We study whether student preferences for certain attributes of friends can predict formation and dissolution of edges in both networks. We introduce a method for computing student preferences for different attributes which we use to predict link formation and dissolution. We then rank these attributes according to their importance for making predictions. We find that personal preferences, in particular political views, and preferences for common activities help predict link formation and dissolution in both the behavioral and cognitive networks.Comment: 12 page

Poboljšana topljivost teško topljivog lijeka u čvrstim disperzijama s polimernim i nepolimernim hidrofilnim dodacima

Irbesartan (IBS) is a hydrophobic drug with poor aqueous solubility and dissolution rate. Solid dispersions (SDs) of IBS were prepared with both small molecules (tartaric acid and mannitol) and polymeric additives (polyvinylpyrrolidone, PVP, and hydroxy propyl methylcellulose, HPMC). A 9.5 and 7 folds enhancement in solubility over the crystalline form (14.6 g mL-1) was observed for tartaric acid (138 g mL-1) and PVP (103 g mL-1), respectively. Powder X-ray diffraction confirmed that IBS existed in the glassy state in all cases, even with excipients having low glass transition temperature. Thermal methods (differential scanning calorimetry and hot stage microscopy) were used to evaluate the miscibility of the drug and additives. These techniques suggested that tartaric acid led to generation of ‘amorphous solutions’ in contrast to ‘amorphous suspensions’ in other three cases. The in vitro dissolution of IBS depended on the additive load and increased with increasing concentration in the case of tartaric acid, an acidifying excipient. The results indicate the suitability of even small molecules for providing solubility benefits, which can be attributed to the good glass forming ability and reasonable ability of IBS to remain in the glassy state.Irbesartan (IBS) je hidrofobni lijek teško topljiv u vodi koji se slabo oslobađa iz ljekovitih pripravaka. U radu je opisana priprava čvrstih disperzija (SDs) IBS-a pomoću aditiva male relativne molekulske mase (vinska kiselina i manitol) i polimera (polivinilpirolidona, PVP, i hidroksipropil metilceluloze, HPMC). Koristeći vinsku kiselinu i PVP topljivost je povećana 9,5 puta (138 g mL1), odnosno 7 puta (103 g mL1) u odnosu na kristaliničnu formu (14,6 g mL1). Difrakcijom X-zrakama praškastog uzorka potvrđeno je da je IBS uvijek u staklastom stanju, pa i s pomoćnim tvarima koje pri niskim temperaturama prelaze u staklasto stanje. Termičke metode (diferencijalna pretražna kalorimetrija i mikroskopija s vrućom pločom) korištene su za procjenu sposobnosti miješanja lijeka s aditivima. Rezultati ukazuju da vinska kiselina stvara amorfnu otopinu, a ostale tvari amorfne suspenzije. Oslobađanje IBS-a in vitro ovisi o količini aditiva i raste s povećanjem koncentracije vinske kiseline, (kisele pomoćne tvari). Poboljšanje topljivosti dodatkom malih molekula može se pripisati sposobnosti prelaska IBS-a u staklasto stanje i sposobnosti zadražavanja u tom stanju

Internal stress affecting environmental fatigue of 7075-T651 alloy

Load history has been known to affect fracture and stress corrosion behavior. The degree to which it affects depends on the severity of the load history. It is known that shop peening can retard the SCC lives markedly in steels. Similarly, prestraining can reduce the KIscc and plateau velocity in high strength steels. These types of experiments are difficult to quantify their effects on the SCC behavior. One can analyze the prestarining effects in a better way by analyzing the effects of single overloads followed by constant applied load to study the behavior. Such experiments can be done by observing the ‘incubation time’ for a crack to initiate in a fatigue pre-cracked sample, at various constant applied loads in a chemical environment. Such experiments have been conducted on a 7075 aluminum alloy for both static and cyclic loads. It is observed that results are similar in behavior. The data indicates the overall behavior can be analyzed by suggesting that the total stress at the crack tip is related to the contributions from chemistry of the environment and an additional factor from “internal stress” that comes from pre-strain. Hence, we can describe the crack initiation & growth criteria in terms of: KIscc = Kapplied + Kinternal stress + Kenvironment \u3e Kthreshold Such trends in the behavior, has been observed in pre-strained steel alloys prior to environmental exposure. The general behavior suggests that the internal stress affects the threshold KIscc more than the plateau velocity. The general SCC behavior is affected by both chemistry and internal stress under external static or cyclic loads