Statistical Mechanics-Inspired Modeling of Heterogeneous Packet Transmission in Communication Networks

This paper presents the qualitative nature of communication network operations as abstraction of typical thermodynamic parameters (e.g., order parameter, temperature, and pressure). Specifically, statistical mechanics-inspired models of critical phenomena (e.g., phase transitions and size scaling) for heterogeneous packet transmission are developed in terms of multiple intensive parameters, namely, the external packet load on the network system and the packet transmission probabilities of heterogeneous packet types. Network phase diagrams are constructed based on these traffic parameters, and decision and control strategies are formulated for heterogeneous packet transmission in the network system. In this context, decision functions and control objectives are derived in closed forms, and the pertinent results of test and validation on a simulated network system are presented.

The nature of 4f electron magnetism in the diluted ferromagnetic Kondo lattice, CeIr2B2

We report on the physical properties of the series Ce(1-x)La(x)Ir(2)B(2) (x = 0-0.9), obtained by means of magnetization, heat capacity and electrical resistivity measurements as a function of temperature (down to 0.7 K for the latter two measurements). The Curie temperature of CeIr(2)B(2) (~5 K) is lowered due to La substitution, as expected. However, no quantum critical point or 'non-Fermi liquid' behavior was observed even in the dilute limit of x = 0.9. Interestingly, ferromagnetic ordering persists even for Ce(0.1)La(0.9)Ir(2)B(2), below 0.8 K. Among the Ce systems, CeIr(2)B(2) is one of the compounds in which direct 4f-4f interaction does not appear to play any role in the magnetism, which is controlled by the indirect exchange interaction alone. In this compound, the Kondo effect persists in the ferromagnetic ordered state, as inferred from the entropy data.

Magnetic anomalies in CeIn(2)

The magnetic behavior of binary compound CeIn(2) has been reported to be unusual in the sense that this compound appears to exhibit a first-order ferromagnetic transition at a rather high temperature of (T(C)=)22 K, which is not so common for Ce systems. In order to throw more light on the magnetic behavior of this compound, we have carried out detailed magnetization, and electrical resistivity studies as a function of temperature, magnetic field and external pressure, in addition to heat-capacity measurements. The plots of H/M versus M(2) at low fields are interestingly characterized by negative slopes, not only near T(C), but also at lower temperatures, a source of which could be attributed to magnetic-field-induced transitions at much lower temperatures. The sign of magnetoresistance tends to change from positive to negative with increasing temperature, as though there is a gradual change in the magnetic character. Finally, the magnetic ordering temperature increases with increasing pressure (until 20 kbar), as though this compound lies at the left-hand side of the peak in Doniach’s magnetic phase diagram.

A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3

We present magnetic characterization of a binary rare-earth intermetallic compound Er(5)Si(3), crystallizing in Mn(5)Si(3)-type hexagonal structure, through magnetization, heat capacity, electrical resistivity and magnetoresistance measurements. Our investigations confirm that the compound exhibits two magnetic transitions with decreasing temperature, the first one at 35 K and the second one at 15 K. The present results reveal that the second magnetic transition is a disorder-broadened first-order transition, as shown by thermal hysteresis in the measured data. Another important finding is that, below 15 K, there is a magnetic-field-induced transition with a hysteretic effect with the electrical resistance getting unusually enhanced at this transition and the magnetoresistance is found to exhibit intriguing magnetic-field dependence, indicating novel magnetic phase coexistence phenomenon. It thus appears that this compound is characterized by interesting magnetic anomalies in the temperature-magnetic-field phase diagram.

Evolution of a metastable phase with a magnetic phase coexistence phenomenon and its unusual sensitivity to magnetic field cycling in the alloys Tb(5 - x)Lu(x)Si3 (x ≤ 0.7)

Recently, we reported an anomalous enhancement of the positive magnetoresistance beyond a critical magnetic field in Tb(5)Si(3) in the magnetically ordered state, attributable to 'inverse metamagnetism'. This results in unusual magnetic hysteresis loops for the pressurized specimens, which are relevant to the topic of 'electronic phase separation'. In this paper, we report the influence of small substitutions of Lu for Tb, to show the evolution of these magnetic anomalies. We find that, at low temperatures, the high-field high-resistivity phase could be partially stabilized on returning the magnetic field to zero in many of these Lu substituted alloys, as measured through the electrical resistivity (ρ). Also, the relative fractions of this phase and the virgin phase appear to be controlled by a small tuning of the composition and temperature. Interestingly, at 1.8 K a sudden 'switch-over' of the value of ρ for this mixed phase to that for the virgin phase for some compositions is observed at low fields after a few field cycles, indicating metastability of this mixed phase.

Magnetism of fine particles of Kondo lattices, obtained by high-energy ball-milling

Despite intense research in the field of strongly correlated electron behavior for the past few decades, there has been very little effort to understand this phenomenon in nanoparticles of the Kondo lattices. In this paper, we review the results of our investigation on the fine particles (<<1 μm) of some of the alloys obtained by high-energy ball-milling, to bring out that this synthetic method paves a way to study strong electron correlations in nanocrystals of such alloys. We primarily focus on the alloys of the series CeRu(2 - x)Rh(x)Si2, lying at different positions in Doniach's magnetic phase diagram. While CeRu2Si2, a bulk paramagnet, appears to become magnetic (of a glassy type) below about 8 K in fine particle form, in CeRh2Si2, an antiferromagnet (T(N) = 36 K) in bulk form, magnetism is destroyed (at least down to 0.5 K) in fine particles. In the alloy CeRu0.8Rh1.2Si2, at the quantum critical point known to exhibit non-Fermi liquid behavior in the bulk form, no long range magnetic ordering is found.

Enhanced electrical resistance at the field-induced magnetic transitions in some non-stoichiometric and stoichiometric Tb-based ternary germanides

We present the magnetic and transport behavior of some Tb compounds, namely TbIrGe(2), TbFe(0.4)Ge(2) and TbCo(0.4)Ge(2). The stoichiometric germanide TbIrGe(2) exhibits at least two distinct magnetic transitions in a close temperature interval around 10 K. Non-stoichiometric compounds, TbFe(0.4)Ge(2) and TbCo(0.4)Ge(2), undergo magnetic ordering around 17 and 19 K, respectively. The magnetic state of these compounds appears to be antiferromagnetic-like. Qualitatively there is a correlation between the field response of the magnetization (M), the magnetoresistance (MR) and the entropy change (ΔS) curve in all three compounds. That is, these Tb compounds exhibit a positive MR and ΔS beyond a magnetic field where M also shows a field-induced transition. On the basis of this correlation, we conclude that magnetic disorder/fluctuations beyond a critical field-a phenomenon called 'inverse metamagnetism'-rather than metamagnetism is induced in these compounds.

Magnetic behavior of bulk and fine particles of RCr2Si2C (R = La, Ce) compounds: possible magnetic ordering from Cr

The magnetic behavior of the quaternary compounds, RCr(2)Si(2)C (R = La, Ce), has been investigated by magnetization (M) and heat-capacity (C) measurements (1.8-300 K) in the bulk polycrystals and nano forms (<1 µm) obtained by high-energy balling. Our finding is that Cr appears to exhibit magnetic ordering of an itinerant type at low temperatures (<20 K) in the bulk form, as inferred from a combined look at all the data. The magnetic ordering gets gradually suppressed with increasing milling time. Evidence for a mixed-valence state of Ce for the bulk form is obtained from the tendency of magnetic susceptibility to exhibit a maximum above 300 K. However, this feature vanishes in the nano form, which exhibits a Curie-Weiss behavior above 200 K as though Ce tends towards trivalency in these fine particles; in addition, there is a weak upturn in C/T below 10 K in the bulk, which becomes very prominent in the milled Ce-based specimens at lower temperatures, as though heavy-fermion behavior gets stronger in smaller particles.

Hydrogen sensing characteristics of wet chemical synthesized tailored Mg0.5Zn0.5Fe2O4 nanostructures

Solution based synthesis routes are attractive for making tailor-made nanostructures for electroceramics in a simple and cost-effective way. The gas sensing characteristics of semiconducting oxide gas sensors strongly depend on the adsorption and desorption of gases over the sensing surface. The morphology of the sensing element is known to influence the adsorption and desorption of gases and thereby the sensing performance of the material. In the present work a Pechini based solution synthesis route is adopted in order to synthesize magnesium zinc ferrite gas sensors in nanoparticle, nanotube and thin film forms. The hydrogen gas sensing characteristics of these sensing elements are compared as a function of test gas concentration and operating temperature. The influences of the morphology of the magnesium zinc ferrite sensing elements on the hydrogen sensing characteristics are discussed.

Reducing gas sensing behavior of nano-crystalline magnesium-zinc ferrite powders

As an effective alternative of simple binary oxides, cubic spinel oxides are considered to be attractive to make sensitive and stable gas sensor, selective to a specific gas. We have focused the present work on the investigation of the gas sensing characteristics of cubic spinel based nano-crystalline magnesium zinc ferrite powders. A wet chemical synthesis route is adopted to synthesize nano-crystalline magnesium zinc ferrite powders. The phase formation behavior and microstructure evolution of the synthesized powder has been investigated using infrared spectroscopy in conjunction with X-ray diffraction analyses and electron microscopy. The n-type semiconducting magnesium-zinc ferrite ceramic exhibits reasonably good sensitivity towards a variety of gases including carbon monoxide, hydrogen, methane and nitrous oxide. It is demonstrated that these sensors can be made selective to hydrogen gas sensing by modulating the operating temperature. The conductance transients during response and recovery processes have been modeled using Langmuir adsorption isotherm and activation energies for gas adsorption and desorption processes have been estimated from the respective thermally activated kinetic processes.

Enhancing bioavailability and hepatoprotective activity of andrographolide from Andrographis paniculata, a well-known medicinal food, through its herbosome

BACKGROUND

Andrographis paniculata is a health food used extensively in Southeast Asia, India and China and contains the pharmacologically important phytochemical andrographolide. Although andrographolide has antihepatotoxic activity, its bioavailability from A. paniculata is restricted by its rapid clearance and high plasma protein binding. The aim of this study was to formulate a herbosome of andrographolide with a naturally occurring phospholipid in order to enhance the bioavailability and hepatoprotective activity of andrographolide in rats.

RESULTS

Andrographolide herbosome equivalent to 25 and 50 mg kg(-1) andrographolide significantly protected the liver of rats, restoring hepatic enzyme activities with respect to carbon tetrachloride-treated animals (P < 0.05 and P < 0.01 respectively). The rat plasma concentration of andrographolide obtained from the complex equivalent to 25 mg kg(-1) andrographolide (C(max) = 9.64 microg mL(-1)) was higher than that obtained from 25 mg kg(-1) andrographolide (C(max) = 6.79 microg mL(-1)), and the complex maintained its effective plasma concentration for a longer period of time.

CONCLUSION

The results proved that the andrographolide complex produced by this method has better bioavailability and hence improved hepatoprotective activity compared with andrographolide at the same dose. Andrographolide complexation is therefore helpful in solving the problem of rapid clearance and low elimination half-life associated with andrographolide from A. paniculata.

Magnetic and electrical transport anomalies of RMAs(2) (R = Pr and Sm, M = Ag and Au)

The results of magnetization, heat capacity and electrical resistivity (ρ) studies of the compounds RMAs(2) (R = Pr and Sm; M = Ag, Au), crystallizing in an HfCuSi(2)-derived structure, are reported. PrAgAs(2) orders antiferromagnetically at T(N) = 5 K. The Au analog, however, does not exhibit long range magnetic order down to 1.8 K. We infer that this is due to subtle differences in their crystallographic features, particularly noting that both the Sm compounds with identical crystal structures as that of the former order magnetically nearly at the same temperature (about 17 K). It appears that, in PrAgAs(2), SmAgAs(2) and SmAuAs(2), there is an additional magnetic transition at a lower temperature, as though the similarity in the crystal structure results in similarities in magnetism as well. The ρ for PrAgAs(2) and PrAuAs(2) exhibits a negative temperature coefficient in some temperature range in the paramagnetic state. SmAuAs(2) exhibits a magnetic Brillouin-zone gap effect in ρ at T(N), while SmAgAs(2) shows a well-defined broad minimum well above T(N) around 45 K. Thus, these compounds reveal interesting magnetic and transport properties.