769 research outputs found
Rh(III)-catalyzed traceless coupling of quinoline N-oxides with Internal diarylalkynes
No full textQuinoline N-oxides were found to undergo
Cp*Rh(III)-catalyzed coupling with internal diarylalkynes to
provide 8-functionalized quinolines through a cascade process
that involves remote C−H bond activation, alkyne insertion,
and intramolecular oxygen atom transfer. In this reaction, the
N-oxide plays a dual role, acting as a traceless directing group as
well as a source of oxygen atom, as confirmed by an 18O-labeling
experiment.193951sciescopu
Planetary Boundary Layer (PBL) monitoring by means of two Laser radar systems: experimental results and comparison.
No full textThe PBL is the lower layer of the atmosphere that is sensitive to the effect of the Earth’s surface, it controls the flow of heat and momentum between the surface and the free atmosphere, thus playing a key role in atmospheric circulation.
At University of Rome “Tor Vergata”, Quantum Electronic and Plasma Laboratories (EQP), two mobile Light Detection and Ranging (LIDAR) systems have been developed. With these systems the monitoring of the Planetary Boundary Layer (PBL) has been performed.
The first mobile Lidar system is based on a pulsed Nd:YAG Q-Switched laser source operating at three wavelengths: 1064 nm, 532 nm and 355 nm. Acquiring the elastic backscattered signals, it has been possible to estimate the aerosolitic backscattering coefficient at the aim to reconstruct the vertical aerosol profiles.
The second one is a Differential Absorption Lidar system (DIAL), composed by a CO2 laser, working in the window spectral range between 9 and 11!m. With this system it has been estimated the water vapour concentration in the PBL region using the two wavelengths 10R20 (10.591 !m) and 10R18 (10.571 !m), which represent, respectively, the absorbing wavelength and non-absorbing one of the water molecule. The comparison of the backscattered radiation at these wavelengths yields the trace gas number density as a function of distance along the field-of-view of the receiving telescope.
Diurnal and nocturnal measurements have been performed simultaneity using the two Lidar/Dial systems. Vertical profiles of the aerosolitic backscattering coefficient and water vapour concentration profiles have been estimated. The results and their comparison will be present in this work
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Judicial review ::process, powers, and problems : essays in honour of Upendra Baxi /
No full textIn India, judicial review is not a static phenomenon. It has ensured that the Constitution is the supreme law of the land, and in situations when a law impinges on the rights and the liberties of citizens, it can be pruned or made void. This is a collection of scholarly essays demonstrating the different facets of judicial review based on the vast area of comparative constitutional law. Importantly, it honours the body of work of Upendra Baxi, legal scholar and author, whose contributions have shaped our understanding of legal jurisprudence and expanded the scope of social transformation in India. This volume recognizes his role as an Indian jurist. Various constitutional law experts come together to reflect on his expositions on the role of the apex court, judicial activism, accountability of judiciary, laws on surrogacy and adultery and so on
sj-docx-2-pie-10.1177_09544089231190754 - Supplemental material for Experimental analysis of a diesel engine run on non-conventional fuel blend at different preheating temperatures
No full textSupplemental material, sj-docx-2-pie-10.1177_09544089231190754 for Experimental analysis of a diesel engine run on non-conventional fuel blend at different preheating temperatures by Rahul Kumar, Anil Singh Yadav, Abhishek Sharma, Upendra Rajak, Tikendra Nath Verma, Tabish Alam, Nishant Tiwari and C P Jawahar in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p
sj-docx-1-pie-10.1177_09544089231190754 - Supplemental material for Experimental analysis of a diesel engine run on non-conventional fuel blend at different preheating temperatures
No full textSupplemental material, sj-docx-1-pie-10.1177_09544089231190754 for Experimental analysis of a diesel engine run on non-conventional fuel blend at different preheating temperatures by Rahul Kumar, Anil Singh Yadav, Abhishek Sharma, Upendra Rajak, Tikendra Nath Verma, Tabish Alam, Nishant Tiwari and C P Jawahar in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p
Global law and human rights: Marxist reflections. How can a political account of human rights avoid Eurocentrism?
No full textMy recent book The Degradation of the International Legal Order? attempts a political account of human rights, and engages with the work of China Miéville and Susan Marks, as well as the extraordinary opus of Alain Badiou. The book has been well received. Sympathetic reviews by Robert Knox and Upendra Baxi have levelled a number of constructive criticisms, and this paper seeks both to grapple with the issues raised and to take the project forward. What is at stake is the concretisation of a thoroughly materialist, properly communist historicisation of human rights, as a contribution to contemporary struggles. In particular, is this project in any sense necessarily Eurocentric
Synthesis, Structural Properties and Upconversion Emission of Er3+ and Er3+/Yb3+ Doped Nanocrystalline NaNbO3
No full textNanocrystalline sodium niobate (NaNbO3) powders doped with Er3+ and Er3+/Yb3+ ions have been successfully synthesized via Pechini sol–gel method for the first time. The prepared NaNbO3 nanocrystalline compounds are single phase, with orthorhombic structure, and have an average particle size of 60 nm. The Raman investigation reveals a disorder nature of the host. Upon near infrared excitation with an 970 nm radiation, an intense
green and a weaker red upconversion emission was observed from the 2H11/2, 4S3/2 4I15/2 and 4F9/2 4I15/2 transitions respectively, along with 1.55 !m emission from 4F13/2 !4I15/2 transition for both Er3+ doped and Er3+/Yb3+ codoped NaNbO3. A two photon process is found to be the origin of the upconverted emission. An enhancement of nearly 30 times of the upconverted emission is observed in the Er3+/Yb3+ codoped than the Er3+ doped NaNbO3, suggesting a possible use of the present materials in field where the upconversion properties can be useful, such as in solar cells or biomedical applications
Fluorescence properties of Nd3+-doped tellurite glasses
No full textThe compositional and concentration dependence of luminescence of the F-4(3/2) -> I-4(J) (J = 13/2, 11/2 and 9/2) transitions in four Nd3+-doped tellurite based glasses has been studied. The free-ion energy levels obtained for 60TeO(2) + 39ZnO(2) + 1.0Nd(2)O(3) (TZN10) glass have been analysed using the free-ion Hamiltonian model and compared with similar results obtained for Nd3+ :glass systems. The absorption spectrum of TZN10 glass has been analysed using the Judd-Ofelt theory. Relatively longer decay rates have been obtained for Nd3+-doped phosphotellurite glasses. The emission characteristics of the F-4(3/2) -> I-4(11/2) transition, of the Nd3+ :TZN10 glass, are found to be comparable to those obtained for Nd3+ :phosphate laser glasses. The non-exponential shape of the emission decay curves for the F-4(3/2) -> I-4(11/2) transition is attributed to the presence of energy transfer processes between the Nd3+ ions
Development of Cryocooler Based High Performance Cryosorption Pump
No full textThe aim of this work is to develop high performance cryosorption (or cryoadsorption) pumps specifically for fusion applications. An actual cryopump for the above application will use the supercritical liquid helium flow through the channels embedded in the large scale cryopanels. In this case, the liquid helium requirement (both as normal and as supercritical fluids) will be large, depending on the size of the cryosorption pump. However, in a research laboratory wherein such large quantities of liquid helium are not available, an alternate arrangement of cooling the cryopanels has to be considered.
One of the possible options can then be as follows. A scaled-down version of the cryopanel can be used and cooled by a two stage cryo-refrigerator system with adequate cooling power. This system is known as cryocooler based cryosorption pump. Due to the availability of a two stage GM cryocooler with a refrigeration power of ~ 1.5 W at 4.2 K in our laboratory, which can be used for the above purpose, the main objective of this work is the “development of a cryocooler based high performance cryosorption pump”.
The cryopanel which is mounted on the second stage cold head of the cryocooler is not necessarily a single panel, but is usually a set of panels (stacked one over the other) and consists of mainly three components and they are: (a) the metallic panel made of copper and cooled by the cryocooler (b) the adhesive to bind the adsorbent onto the metallic panel and (c) the adsorbent (in the present case, activated carbon (AC)) which is used to adsorb the gas molecules. By this arrangement, the adsorbent gets cooled to the lowest possible temperature to enable cryopumping.
To develop the cryocooler based high performance cryosorption pump, we need to select: (a) the best adsorbent (with large adsorption surface area) and adhere it on a cryopanel to evaluate its performance as a cryopump and (b) the best adhesive with high thermal conductivity, high bonding strength and ability to withstand several thermal cycles.
The surface area of an adsorbent in the range of temperatures range from 4.5 K to 77 K can be arrived at by a micropore analyser ( Model: ASIQ, Quantachrome, USA) integrated with a two stage GM cryocooler (Janis: SRDK415D), with helium as adsorbate gas at 4.5 K and nitrogen as adsorbate gas at 77 K. Based on the above studies, we can choose the best activated carbon with high surface area.
Next, the best adhesive which is used for binding the adsorbent onto the panel is chosen on the basis of its high thermal conductivity. The thermal conductivity of the adhesive has been measured using two dedicated thermal conductivity measurement systems namely: (a) liquid helium based Janis SuperVariTemp (SVT) cryostat and (b) two-stage GM cryocooler based experimental setup developed in our laboratory in the temperature range from 4.5 K to 300 K.
In order to make comparative studies of cryosorption of different activated carbons, a standard cryopanel, such as the one used in the commercial cryopump (Make: Varian, Model Ebara SP8) has been chosen in our studies. (Henceforth, this will be designated as “Commercial cryopanel”). In other words, the physical dimensions of all the cryopanels fabricated with indigenous activated carbons are exactly the same as that of the commercial cryopanel. By this, the experimental results of pumping speeds of different indigenous AC cryopanels can be benchmarked against the commercial cryopanel and the best performing activated carbon cryopanel can be arrived at.
In the following, we discuss the works carried out for the development of the cryocooler based high performance cryosorption pump.
a) A specially prepared indigenously developed Knitted Carbon Cloth (KCC/IIS01) is found to have a larger surface area for adsorption compared to the other adsorbents. This adsorbent has a surface area of ~ 3000 m2/g for helium adsorption at 4.5 K, which is significantly higher than those of granular charcoals which are in the range of ~ 1600 m2/g for similar experimental conditions. This AC cloth has been used for the development of our cryosorption pump.
b) A special epoxy based adhesive (SEBA/IIS01) with higher thermal conductivity, (measured using the experimental setups mentioned earlier) in the temperature range from 4.5 K to 7 K (which is generally the operating temperature range of a cryosorption pump for efficient pumping of helium gas) compared to the commercially available epoxy adhesives such as STYCAST 2850 FT and G10 Cryocomp has been developed indigenously and used.
c) Using the above Knitted Carbon Cloth KCC/IIS01 and the epoxy adhesive SEBA/IIS01, cryopanel has been prepared and studied for its performance. The pumping speeds of the developed cryopanel are improved on an average by factors of 1.55 and 1.54 when compared with those of commercial panel for gases such as hydrogen (H2) and helium (He) respectively in the specific pressure range.
To enhance the thermal conductivity of SEBA/IIS01, fine powders of metallic fillers (such as aluminium, silver etc.) can be added to the pure epoxy adhesive. However it is also essential that the epoxy-aluminium composite adhesive should withstand the thermal cycling from 4.5 K to 300 K during its functioning as a cryosorption pump.
d) Now the thermal conductivities of epoxy-aluminium composites in the temperature range from 4.5 K to 300 K has been measured using the dedicated experimental setups for measurements of thermal conductivity (developed in-house). The measurements of thermal conductivity using the above experimental setups are based on one-dimensional Fourier heat conduction with longitudinal steady state heat flow method. Detailed experimental studies on thermal conductivity of epoxy and epoxy-aluminium composites have been carried out by the above experimental setups.
e) Further the thermal conductivities of the epoxy-aluminium composites have been theoretically predicted by analytical heat conduction models. Here, the epoxy forms the base matrix and aluminium powder forms the filler. Appropriate models have been developed both for the low and high volume fractions of the filler in the epoxy base matrix. The thermal conductivity values predicted by the models match quite well with the experimentally measured values of the epoxy-aluminium composite samples. Also the developed models are able to predict the thermal conductivity values of the published data.
f) By the addition of metallic (aluminium) filler particles to the epoxy adhesive, the thermal conductivity of the epoxy adhesive is increased. However, the downside of adding aluminium fine powder is the reduction of the bonding strength of the epoxy onto the cryopanel. An experimental setup has been developed to measure the strength of epoxy- aluminium composite adhesive. Based on the experimental studies, an optimum composition of the aluminium powder filler in the epoxy adhesive has been estimated as ~ 35 % by volume fraction. This epoxy-aluminium composite adhesive is designated henceforth as “EAL35”.
g) A new cryopanel has been fabricated wherein the activated carbon cloth KCC/IIS01 is bonded using EAL35. The pumping speeds of the newly developed cryopanel are improved on an average by factors of 3.63 and 3.60 when compared with those of commercial panel for gases such as hydrogen and helium respectively in the pressure range from 5E-6 to 4E-5 mbar.
Our studies have led to the development of a cryocooler based cryosorption pump with higher pumping speeds for gases such as H2 and He compared to the commercial cryopumps. Hence the present studies will be quite useful to the development of the appropriate cryosorption pumps for the Tokamak related applications
Design of a Vortex Tube based Refrigeration System
No full textVortex tube (VT) is a mechanical device with no moving parts. The fundamental principle of Vortex Tube is that it can split an incoming fluid flow of a constant pressure and constant temperature gas stream into two separate low pressure streams, one having higher enthalpy and the other having lower enthalpy than the inlet flow. So this device essentially works as a temperature separator. On separation from the device, a warmer flow exits through a terminal which is called the “hot end” and a low temperature stream comes out from another terminal known as the “cold end”. Just with a few bar pressure of compressed air at room temperature can produce a hot stream temperature of about 150°C and a cold stream temperature of about - 40°C. This temperature separation scheme allows us to get cooling and heating effect simultaneously using the same device which makes the Vortex tube one of the popular mechanical equipment and is used in many fields of engineering. The cooling or heating effect produced by this device is largely dependent on geometric parameters of the device itself. Since no exact theoretical correlation is there between the geometric parameters and the cooling (or heating) effect produced, VT design is solely based on empirical relations. There are quite a few geometric parameters which affect the cooling effect of this device and all the empirical correlation are needed to design the optimum VT for maximum cooling/heating effect. These relations can be derived in two ways, either by numerical methods or by experimental investigations. The first part of the thesis important geometric parameter of the VT namely the ratio of the “cold end” diameter (to the “tube diameter” , which has been numerically optimized in this work to achieve maximum temperature separation.
In our efforts to design a VT based refrigeration system, optimization of the VT itself is not enough. A suitable heat exchanger (HX) which can extract the cold enthalpy from the VT also needs to be designed and cascaded with the VT to get the complete refrigeration system. The second part of the thesis is solely dedicated to the design of a suitable HX that can be used alongside a VT to produce refrigeration. The HXs design can be approached from two directions, dimensional aspect and material aspect. Rather than focusing on the dimensional aspect in this work we have concentrated of the material aspect of HX design. It is fairly obvious that the thermal conductivity (TC) of the HX material will play a crucial role on the cooling effect of the refrigeration system. Conventional metals with high TC can be used to design HXs but the downsides of using pure metals such as Copper, Iron are that they are heavy, quite expensive and highly reactive to corrosive fluids. Because of this, high TC ceramic material such as Aluminium Nitride (AlN) is quite often used to fabricate HXs and they are used for spot cooling in electronic systems. AlN has TC of 160 W/m-K which is high but not as high as of Copper or Iron. TC of AlN can be increased by mixing the right volume fraction of metal powder (such as pure Aluminium) with it to a great extent. So in a nutshell, instead of using pure AlN, if we use the particle reinforced binary composite [AlN + Al (powder)] to design a HX, we would achieve the benefits of having high TC as well as properties such as anti-corrosiveness, cost effectiveness and weight reduction.
In the above context, prediction of TC of particle reinforced composite materials containing a base material of low TC and a filler material of high TC is of utmost importance. Till now a very few analytical heat transfer models are available in the literature that can accurately predict the TC value of such composites especially when high volume fraction of filler particles is added to the base material or if more than one type of filler particles are added. So in this thesis, three analytical heat transfer models have been developed that can predict the TC of binary as well as tertiary particle reinforced composites.
The third and the final segment of the thesis deals with the performance study of a refrigeration system comprised of the optimized VT cascaded with a suitable HX made out of a particle reinforced composite material. The numerical results show how the HX effectiveness improves as the volume fraction of the filler particles in the composite increases.
The key results of the works described in the thesis are as follows:
• Through extensive numerical simulations it is shown that for = 0.5, the temperature separation in a VT is maximum.
• The heat transfer models developed to predict the thermal conductivity of binary composites, shows the trend of how thermal conductivity varies with increasing volume fraction of filler. It has been shown that initially the thermal conductivity increases linearly with a small slope, then after a critical volume fraction an abrupt increment of slope is observed due to the formation of continuous heat conduction paths within the composite. Further increase in volume fraction shows linear increment of thermal conductivity with lesser slope as before.
• The heat transfer model developed to predict the thermal conductivity of tertiary
composites is suitable for low volume fraction (< 20 %). The model shows the addition of one component into the base matrix affects the distribution of the other
component which is observed through the covariance.
• The last part of the thesis shows that compared to a pure AlN heat exchanger, a heat exchanger made of AlN + 30 % volume fraction of pure Aluminium powder, has increased heat exchanger effectiveness by more than 50 %.
Thesis outline is as follows:
• Chapter 1 is a brief introduction to Vortex Tube.
• Chapter 2 deals with the necessary literature review related to Vortex Tube as well as presently available heat transfer models that are equipped to handle composite materials to predict their TC.
• Chapter 3 elaborates numerical modeling and optimization of a critical parameter
( to achieve maximum temperature separation in a VT.
• Chapter 4 presents a stochastic heat transfer model to estimate the TC of Binary particle reinforced composites containing low volume fraction of filler particles.
• Chapter 5 describes the development of a computational heat transfer model to predict the TC of Particle Reinforced Binary Composite materials containing high volume fraction of filler element.
• Chapter 6 deals with a stochastic heat transfer model to calculate TC of Particle Reinforced Tertiary Composite materials containing low volume fractions of filler elements.
• Chapter 7 consolidates all the necessary concepts and data from previous chapters to design the final cascaded VT based refrigeration system and presents a performance study.
• The last chapter summarizes the entire work along with scope for future work
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