FORMULATION AND INVESTIGATION OF POLYMERIC MULTIPLE UNIT PELLET SYSTEMS CONSISTING OF SUSTAINED RELEASE GLIMEPIRIDE AND IMMEDIATE RELEASE ATORVASTATIN CALCIUM

Objective: The objective of the present work was to develop novel fixed-dose combinations (FDCs) for improvement of glucose tolerance in type II diabetes mellitus patients associated with dyslipidemia. Methods: Multiple unit pellet systems (MUPSs) consisting of sustained release (SR) glimepiride and immediate release atorvastatin calcium pellets were formulated. The SR glimepiride pellets were prepared using a combination of locust bean gum and gum ghatti/guar gum. Similarly, the immediate release of atorvastatin calcium pellets was prepared using locust bean gum suspension as a binder. Results: The formulated pellets were characterized using Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC). Further, surface morphology of the formulated pellets was done by scanning electron microscopy (SEM). FT-IR and DSC studies suggested that there were no chemical interactions between the drug and natural polymers. SEM studies revealed that formulated pellets were in spherical shape. Based on in vitro evaluation, the SR glimepiride formulation developed using a combination of 2% locust bean gum and 2.5% gum ghatti polymers sustained the release of the drug up to 12 h. Similarly, the immediate release atorvastatin calcium formulation containing 1% w/w locust bean gum suspension as a binder and 7% croscarmellose sodium showed fast disintegration of pellets. The in vivo studies in albino Wistar rat revealed that there was an improvement in bioavailability of the drugs. Stability studies showed that there were no significant changes in the drug content and physical appearance of the prepared SR glimepiride and immediate release atorvastatin pellet formulations. Conclusion: Thus, the formulated FDC as MUPS can be used as an alternative approach for treating diabetes mellitus-induced dyslipidemia

Heat balance analysis of single stage Gifford-McMahon cycle cryorefrigerator

A heat balance analysis of single stage Gifford-McMahon cycle cryorefrigerator is presented. Ideal refrigeration, actual refrigeration, net refrigeration and the various losses are tabulated. It is observed that pressure-volume losses account for a major fraction of the total losses

Exergy analysis of a Gifford-McMahon cycle cryorefrigerator

Exergy analysis of a Gifford-McMahon cycle refrigerator is presented. Exergy losses occurring in various components are considered and the exergy balance is shown in tabular form. It is observed that the major losses occur in the compressor and at the cold end

Nitrogen system for the SSC

The Superconducting Super Collider consists of two parallel magnet rings, each 87,120 m in circumference, constructed in a tunnel 25 m to 74 m below ground level. They are operated at a controlled low helium temperature in order to maintain the magnet windings in the superconducting state. To obtain this condition, the magnet cryostat is designed with a high-quality insulation obtained by a high vacuum chamber, multilayer insulation, and thermal shields at nominal temperatures of 84 K and 20 K. Thermal radiation and the conduction heat load through the supports are intercepted and absorbed by the 84-K shield. Liquid nitrogen provides the refrigeration for these loads. The 84-K shield is anchored to two 63.5-mm stainless-steel tubes. One of the tubes, the ``liquid line,`` serves as a conduit in the distribution system of liquid nitrogen. The other tube, the ``vapor line,`` is used to collect the nitrogen vapor generated in the cooling process and to supply this vapor to,the helium refrigerators for precooling. The vapor line may also be used as a continuous cooler by injecting controlled amounts of liquid nitrogen. The nitrogen system consists of nitrogen supplies; ten nitrogen dewars for the collider and two for the High Energy Booster located on the ground at the main shaft entrances; liquid and vapor transfer lines through the shaft to connect the surface and the tunnel systems; and transfer lines to bypass warm equipment sections of the collider. The nitrogen system is expected to operate at steady state condition except for cooldown, warmup, and system repair, for which transients are expected. During normal operation and standby modes of the collider, temperature, pressure, and mass flow are expected to be constant in all circuits of the nitrogen system. The conceptual design requirements for various flow schemes and the engineering considerations are presented in this report

Spool valve mechanism used in a 20 K Gifford-McMahon cycle cryorefrigerator and its effect on the P-V diagram

The design and fabrication of a spool valve for a two-stage Gifford-McMahon cycle cryorefrigerator is described. The effect of this valve on the P-V diagram and practical methods of reducing the P-V degradation are also discussed

Two stage Gifford-McMahon cycle cryorefrigerator operating at 20 K

A two stage Gifford-McMahon cycle cryorefrigerator operating at 20 K is described. This refrigerator uses a very simple 'spool valve' and a modified indigenous compressor to compress helium gas. This cryorefrigerator reaches a lowest temperature of 15.5 K; it takes ≈ 50 min to reach 20 K and the cooling capacity is ≈ 2.5 W at 25 K. The cool-down characteristics and load characteristics are presented in graphical form. The effect of changing the operating pressure ratio and the second stage regenerator matrix size are also reported. Pressure-volume (P-V) diagrams obtained at various temperatures indicate that P-V losses form the major fraction of the total losses and this becomes more pronounced as the temperature is decreased. A heat balance analysis shows the relative magnitudes of various losses

Thermal and flow considerations for the 80 K shield of the SSC magnet cryostats

The nominal temperatures in the SSC cryostat range between 4.2 K in the superconducting magnet and 300 K on the cryostat outer wall. To minimize the 4 K heat load, a thermal shield cooled by liquid and vapor nitrogen flows at 84 K and one a 20 K cooled by helium flow are incorporated in the cryostat. Tubes attached to the shields serve as conduits for cryogens. The liquid nitrogen tube in the cryostat is used for cryostat refrigeration and also for liquid distribution around the SSC rings. The second nitrogen line is used to return the vapor to the helium refrigerators for further processing. The nominal GN2 flow from a 4.3-km long cryogenic string (4 sections) to the surface is 64 g/s. The total liquid nitrogen consumption of approximately 5000 g/s will be supplied at one, two or more locations on the surface. The total heat load of the 80 K shield is estimated as 3.2 W/m. About 50% is composed of infrared radiation and remaining 50% by heat conduction through supports, vacuum barriers and other thermal connections between the shield and the 300 K outer wall. The required LN2 flow rate depends on the distribution and circulation schemes. The LN2 temperature will in turn vary depending on the flow rate and on the recooling methods used. For example, with a massflow of 400 g/s of LN2 the temperature rises from 82 K to 86 K between two compact recoolers 1 km apart. This temperature is higher thin desired. The temperature can be reduced by increasing the flow rate of the liquid or by using the continuous recooling. This paper discusses some thermal problems caused by certain mechanical designs of the 80 K shielding the possible improvement by using continuous recooling. In the following, we present results of the 80 K shield temperature distribution analysis, the 20 K shield heat load augmentation resulting from the increased 80 K shield temperatures, the continuous nitrogen recooling scheme and some flow timing related analysis

Spool valve mechanism used in a 20 K Gifford-McMahon cycle cryorefrigerator and its effect on the P-V diagram

The design and fabrication of a spool valve for a two-stage Gifford-McMahon cycle cryorefrigerator is described. The effect of this valve on the P-V diagram and practical methods of reducing the P-V degradation are also discussed