On-chip isoelectric focusing using photopolymerized immobilized pH gradients

We present the first successful adaptation of immobilized pH gradients (IPGs) to the microscale (muIPGs) using a new method for generating precisely defined polymer gradients on-chip. Gradients of monomer were established via diffusion along 6 mm flow-restricted channel segments. Precise control over boundary conditions and the resulting gradient is achieved by continuous flow of stock solutions through side channels flanking the gradient segment. Once the desired gradient is established, it is immobilized via photopolymerization. Precise gradient formation was verified with spatial and temporal detection of a fluorescent dye added to one of the flanking streams. Rapid (<20 min) isoelectric focusing of several fluorescent pI markers and proteins is demonstrated across pH 3.8-7.0 muIPGs using both denaturing and nondenaturing conditions, without the addition of carrier ampholytes. The muIPG format yields improved stability and comparable resolution to prominent on-chip IEF techniques. In addition to rapid, high-resolution separations, the reported muIPG format is amenable to multiplexed and multidimensional analysis via custom gradients as well as integration with other on-chip separation methods.     

Self-assembly and magnetically induced phase transition of three-dimensional colloidal photonic crystals

Charged superparamagnetic colloidal Fe(3)O(4)@SiO(2) core-shell particles were chosen as model dipolar soft spheres to study their crystallization and magnetically induced phase transition in suspensions. The 3D colloidal crystals feature excellent magnetically responsive photonic properties with strong diffraction, fast response and wide tunability.     

Retinoic acid-induced stress protein synthesis in the mouse

We have previously demonstrated that stress proteins (SPs) are synthesized in tissues in which malformations are later observed following treatment with the developmental toxicant, retinoic acid (RA), on day 11 of gestation (GD 11). These proteins were not synthesized in tissues which did not present with malformations near partuition. The purpose of the present investigation was to determine if this correlation between early SP synthesis and later malformation was present at other times during gestation. CD-1 strain mice were dosed orally with corn oil or 100 mg/kg body weight RA on GD 10 or 13. Some of the mice in each group were given an intraperitoneal injection of 3H-leucine to label embryonic protein synthesis one hour after dosing with RA. These animals were sacrificed 1.5 hour later, and embryonic protein synthesis was determined by two-dimensional gel electrophoresis followed by autoradiography. Other animals in each group were sacrificed on day 17 of gestation, and fetuses were examined for the presence of malformations. Following treatment with RA on day 10 of gestation, malformations were observed in the forelimbs, the hindlimbs and the tail; heart defects were not observed. SPs of 20-25,000 and 90,000 relative molecular mass (Mr) were synthesized in the forelimb bud and tail; in addition, a second low molecular weight (20-25,000) and a 84,000 Mr SPs were synthesized in forelimb buds. No SPs were synthesized in the hindlimb bud or the heart. Following RA treatment on GD 13, cleft palate was observed in 58% of fetuses; no other malformations were found. Proteins of 34,000, 84,000 and 90,000 Mr were synthesized in craniofacial tissue; SPs were not observed in forelimb bud, hindlimb bud, heart or tail tissues at this time. Therefore, it appears that there may be a correlation between tissue-specific SP synthesis early in organogenesis and the presence of a malformation later in gestation.     

A Study of the Crystallization, Melting, and Foaming Behaviors of Polylactic Acid in Compressed CO2

The crystallization and melting behaviors of linear polylactic acid (PLA) treated by compressed CO₂ was investigated. The isothermal crystallization test indicated that while PLA exhibited very low crystallization kinetics under atmospheric pressure, CO₂ exposure significantly increased PLA’s crystallization rate; a high crystallinity of 16.5% was achieved after CO₂ treatment for only 1 min at 100 °C and 6.89 MPa. One melting peak could be found in the DSC curve, and this exhibited a slight dependency on treatment times, temperatures, and pressures. PLA samples tended to foam during the gas release process, and a foaming window as a function of time and temperature was established. Based on the foaming window, crystallinity, and cell morphology, it was found that foaming clearly reduced the needed time for PLA’s crystallization equilibrium.     

Separation of ethylene/ethane mixtures by adsorption on small-pored titanosilicate molecular sieves

Adsorptive separation of ethylene and ethane may represent a less energy-intensive alternative to current sub-ambient distillation methods. In this approach, ethylene and ethane are separated by inverse-phase gas chromatographic and gravimetric isotherm techniques on ion-exchanged forms of ETS-4 and RPZ titanosilicate molecular sieves. Gas chromatography reveals that kinetic separation of ethylene from ethane is possible using ETS-4 and RPZ adsorbents exchanged with Zn and mixed Ca/H. Gas chromatographic selectivities of 4–40 for the adsorptive separation of ethylene and ethane were measured for these adsorbents, and the limiting selectivity calculated from gravimetric adsorption isotherms was between 4 and 12. In accordance with the ideal adsorbed solution theory, ethylene/ethane selectivity increases with pressure in all cases studied, especially for strontium- and barium-exchanged ETS-4. Due to the molecular sieving character of the adsorbents, steric effects were observed for the adsorption of ethylene and ethane, and contact time between the adsorbent and the gas mixture was the key factor in the separation of the gases. ETS-4 and RPZ materials exchanged with Zn or Ca/H are excellent candidates for the commercial adsorptive separation of ethylene and ethane.     

Adsorption of ethane and ethylene on modified ETS-10

Ethylene and ethane adsorption isotherms were measured for Engelhard Titanosilicate (ETS-10) both as made in the sodium form and ion exchanged with different mono-, di-, and trivalent cations. Isotherms for Na-, K-, and Ag-ETS-10 were found to be nearly rectangular indicating very strong adsorption. In contrast, isotherms for Li-, Ba-, and Cu-ETS-10 show substantial curvature. Isotherms for some mixed cation forms (such as Ba/H and La/H) demonstrate the weakest adsorption with substantial adsorption swing capacity between 1 and 200 kPa. Using the ideal adsorption solution theory (IAST), it was determined that ethylene/ethane adsorption selectivity decreases in the order Na>K>Li>Cu≈Ba>Ba/H>La/H, while the adsorption swing capacity (from 1 to 200 kPa) shows an exactly reversed trend. It is thus probable to find the right balance between selectivity and swing capacity in order to design appropriate pressure swing adsorption (PSA) processes for the separation of ethylene and ethane under a wide range of conditions.     

Influence of PFA on cracking of concrete and cement paste after exposure to high temperatures

Cracking is a visible type of damage to concrete that has significant adverse effects on the mechanical and durability properties of concrete. An experimental study on the identification and quantification of cracking in postheated concrete was conducted to provide a better understanding of the mechanisms of damages to concrete after exposure to high temperatures. In addition to the quantification of the residual compressive and tensile strengths of concrete after high temperature exposure, both macroscale and microscopic cracks were observed and measured. The crack patterns in different concretes, including concrete made with different water to binder (w/b) ratios and PFA dosages, were classified. Also examined was the cracking in the corresponding hardened cement pastes (hcp's) prepared without adding aggregates. The relation of cracking with deterioration of the durability properties of concrete, with respect to the chloride diffusion test results, was discussed. Crack density, a quantitative term, which had been introduced to study the microcrack properties in concrete, was adopted for measuring the severity of cracking. Severe cracking of concrete was observed after exposure to 450 °C and higher temperatures. The presence of PFA reduced the extent of these thermal cracks.     

A Polymer Visualization System with Accurate Heating and Cooling Control and High-Speed Imaging

A visualization system to observe crystal and bubble formation in polymers under high temperature and pressure has been developed. Using this system, polymer can be subjected to a programmable thermal treatment to simulate the process in high pressure differential scanning calorimetry (HPDSC). With a high-temperature/high-pressure view-cell unit, this system enables in situ observation of crystal formation in semi-crystalline polymers to complement thermal analyses with HPDSC. The high-speed recording capability of the camera not only allows detailed recording of crystal formation, it also enables in situ capture of plastic foaming processes with a high temporal resolution. To demonstrate the system’s capability, crystal formation and foaming processes of polypropylene/carbon dioxide systems were examined. It was observed that crystals nucleated and grew into spherulites, and they grew at faster rates as temperature decreased. This observation agrees with the crystallinity measurement obtained with the HPDSC. Cell nucleation first occurred at crystals’ boundaries due to CO₂ exclusion from crystal growth fronts. Subsequently, cells were nucleated around the existing ones due to tensile stresses generated in the constrained amorphous regions between networks of crystals.     

Identification of amino acid residues of the NR2A subunit that control glutamate potency in recombinant NR1/NR2A NMDA receptors

The NMDA type of ligand-gated glutamate receptor requires the presence of both glutamate and glycine for gating. These receptors are hetero-oligomers of NR1 and NR2 subunits. Previously it was thought that the binding sites for glycine and glutamate were formed by residues on the NR1 subunit. Indeed, it has been shown that the effects of glycine are controlled by residues on the NR1 subunit, and a "Venus flytrap" model for the glycine binding site has been suggested by analogy with bacterial periplasmic amino acid binding proteins. By analysis of 10 mutant NMDA receptors, we now show that residues on the NR2A subunit control glutamate potency in recombinant NR1/NR2A receptors, without affecting glycine potency. Furthermore, we provide evidence that, at least for some mutated residues, the reduced potency of glutamate cannot be explained by alteration of gating but has to be caused primarily by impairing the binding of the agonist to the resting state of the receptor. One NR2A mutant, NR2A(T671A), had an EC50 for glutamate 1000-fold greater than wild type and a 255-fold reduced affinity for APV, yet it had single-channel openings very similar to those of wild type. Therefore we propose that the glutamate binding site is located on NR2 subunits and (taking our data together with previous work) is not on the NR1 subunit. Our data further imply that each NMDA receptor subunit possesses a binding site for an agonist (glutamate or glycine).     

Referrals for alternative therapies

BACKGROUND: The purpose of this study was to examine how allopathic physicians participate in the decision to refer patients for alternative therapies. METHODS: A pretested, self-administered, structured questionnaire was distributed simultaneously to all area physicians at community locations in Washington State, New Mexico, and southern Israel. The primary outcome measures were monthly and yearly rates of referral to alternative therapies. RESULTS: More than 60% of all physicians made referrals to alternative providers at least once in the preceding year and 38% in the preceding month. Referrals were generally based on patient requests, synergy between the alternative therapy and the patients' cultural beliefs, failure of conventional treatment, and the belief that patients have "nonorganic" or "psychological" disease. There was no relationship between the rate of referral and the referring physician's level of knowledge about, beliefs about the effectiveness of, or familiarity with alternative therapies. CONCLUSIONS: Primary care physicians are more likely than other medical specialists to be knowledgeable about, personally subscribe to, and refer patients for alternative therapies. Physicians who use alternative techniques for themselves and their families or who adopt complementary therapies into their practices have higher rates of referrals. Referral rates and patterns were similar between sites despite considerable cross-cultural and health system differences. Given the high rate of referral and the absence of an apparent internal logic for such recommendations, guidelines and physician education may be advisable.