Cellular Carriers Research Articles

Wireless location privacy protection

After more than two decades of hype, computing and communication technologies are finally converging. Java-enabled cell phones run a host of powerful applications including mobile Internet access, while many notebook computers offer high-speed wireless connectivity as a standard feature. The big decision when purchasing a PDA is whether to get integrated cellular service or Wi-Fi capability. Location-based services are emerging as the next killer app in personal wireless devices, but there are few safeguards on location privacy. In fact, the demand for improved public safety is pushing regulation in the opposite direction. Today, when a person reports an emergency from a landline phone by dialing 911 in the United States or 112 in Europe, the system displays the caller's phone number and address to the dispatcher. The US Federal Communications Commission has mandated that, by December 2005, all cellular carriers be able to identify the location of emergency callers using mobile phones to within 50 to 100 meters. However, how cellular carriers and other businesses will use this capability remains open to question. The article looks at some of the areas this capability affects, including: privacy risks; economic damages; location-based spam; intermittent connectivity; user interfaces; network privacy; and privacy protection.

Regulation of phyllotaxis by polar auxin transport.

The regular arrangement of leaves around a plant's stem, called phyllotaxis, has for centuries attracted the attention of philosophers, mathematicians and natural scientists; however, to date, studies of phyllotaxis have been largely theoretical. Leaves and flowers are formed from the shoot apical meristem, triggered by the plant hormone auxin. Auxin is transported through plant tissues by specific cellular influx and efflux carrier proteins. Here we show that proteins involved in auxin transport regulate phyllotaxis. Our data indicate that auxin is transported upwards into the meristem through the epidermis and the outermost meristem cell layer. Existing leaf primordia act as sinks, redistributing auxin and creating its heterogeneous distribution in the meristem. Auxin accumulation occurs only at certain minimal distances from existing primordia, defining the position of future primordia. This model for phyllotaxis accounts for its reiterative nature, as well as its regularity and stability.

Characterization of cellular carriers for use in injectable tissue-engineering composites.

Injectable composite tissue-engineering scaffolds are systems that incorporate individual cell carriers within a gel delivery matrix. This study assessed low-temperature casting as a possible method to produce synthetic cell-carrier beads. Porous poly-L-lactide beads were manufactured by low-temperature casting. Two porogens, either glucose or sodium chloride, were incorporated into the beads and subsequently leached. Beads were seeded with primary culture aortic smooth muscle rat cells and were evaluated over a 13-day period using a series of chemical, biochemical, and histological assays. Results indicate that low-temperature casting is a viable technique to produce injectable beads on the order of 1.5-2.0 mm. The manufactured beads supported smooth muscle cell attachment and proliferation; where the beads formed with sodium chloride allowed enhanced proliferation. Differences in physical qualities, namely buoyancy and topography, were dependent on porogen selection and may provide a mechanism for bead and composite customization.

Carrier Erythrocytes: An Overview

Application of erythrocytes, the most abundant cells of the human body with desirable physiologic and morphologic characteristics, in drug delivery has been exploited extensively. These cellular carriers, having remarkable biocompatibility, biodegradability, and life-span in circulation, can be loaded by a wide spectrum of compounds of therapeutic value using different chemically, as well as physically, based methods. Most of the characteristics of the erythrocytes, including shape, membrane fragility, deformability, and hematologic indices undergo some degree of irreversible changes during the loading procedure. The efflux pattern of the encapsulated compounds from the carrier erythrocytes covers a wide range between a relatively rapid release (complete release within a few hours) and no detectable release until the cell lysis. A series of methods have been tested successfully for improvement of in vitro storability of the carrier erythrocytes without any significant changes in cell biology as well as drug delivery efficacy. Carrier erythrocytes have been exploited for several potential applications, including intravenous slow release of therapeutic agents, enzyme therapy, drug targeting to reticuloendothelial system (RES), improvement of oxygen delivery to tissues, and preparation of fused cells.

Wireless Personal Communications special issue onCellular and Wireless Location Based Technologies and Services

Even before the launch of packet switched services in cellular systems, a large number of network operators and manufactures were working on the development of Location Based Technologies and Services. Location is a strategic asset of cellular and wireless carriers. Leveraging this information enables the user to experience value-added services and the mobile network operator to offer differentiation and incremental profitability. Moreover, exploiting location information to improve network planning and performance is very promising issue for the near future.

Beta-ketoacyl acyl carrier protein reductase (FabG) activity of the fatty acid biosynthetic pathway is a determining factor of 3-oxo-homoserine lactone acyl chain lengths.

The two acyl-homoserine lactones (AHLs) N-(butyryl)-L-homoserine lactone and N-[3-oxododecanoyl]-L-homoserine lactone (3-oxo-C(12)-HSL) are required for quorum sensing in Pseudomonas aeruginosa. These AHLs derive their invariant lactone rings from S-adenosylmethionine and their variable acyl chains from the cellular acyl-acyl carrier protein (ACP) pool. This reaction is catalysed by specific AHL synthases, which exhibit acyl chain specificity. Culture supernatants of P. aeruginosa contain multiple 3-oxo-AHLs that differ in their acyl chain lengths but their physiological role, if any, remains unknown. An in vitro fatty acid-3-oxo-AHL synthesis system was established utilizing purified P. aeruginosa Fab proteins, ACP and the LasI 3-oxo-AHL synthase. In the presence of excess protein, substrates and cofactors, this system produced almost exclusively 3-oxo-C(12)-HSL. When the beta-ketoacyl-ACP reductase (FabG) catalysed step was made rate-limiting by switching from the preferred NADPH cofactor to NADH, increased levels of short chain 3-oxo-AHLs were produced, presumably because shorter-chain ketoacyl-ACPs accumulated and thus became LasI substrates. Consistent with these in vitro observations, a fabG(Ts) mutant produced increased amounts of 3-oxo-AHLs in vivo. Thus, in vitro and in vivo evidence indicated that modulation of FabG activity of the fatty acid biosynthetic pathway may determine the acyl chain lengths of these 3-oxo-AHLs and that the LasI 3-oxo-AHL synthase is sufficient for their synthesis.

Isolation, Characterization, and cDNA Sequence of a Carotenoid Binding Protein from the Silk Gland of Bombyx mori Larvae

A carotenoid binding protein (CBP) has been isolated from the silk glands of Bombyx mori larvae. The protein has an apparent molecular mass of 33 kDa and binds carotenoids in a 1:1 molar ratio. Lutein accounts for 90% of the bound carotenoids, whereas alpha-carotene and beta-carotene are minor components. Immunological analysis demonstrated the presence of CBP only in the yellow-colored tissues of the silk gland, midgut, testis, and ovary. Several phenotypes of B. mori mutants linked to carotenoid transport have been utilized to characterize CBP. The Y (yellow hemolymph) gene controls uptake of carotenoids from the midgut lumen into the midgut epithelium, and larvae with the +(Y) gene lack this property. Immunoblotting analysis confirmed the presence of CBP in mutants with the dominant Y gene only. Immunohistochemistry verified the localization of CBP in the villi of the midgut epithelium, indicating that CBP might be involved in absorption of carotenoids. A cDNA clone for CBP encoding a protein of 297 amino acids has been isolated from the B. mori silk gland cDNA library. The deduced amino acid sequence revealed that CBP is a novel member of the steroidogenic acute regulatory (StAR) protein family with its unique structural feature of a StAR-related lipid transfer domain, known to aid in lipid transfer and recognition. Lutein-binding capacity of the recombinant CBP (rCBP) determined by incubating rCBP with lutein followed by immunoprecipitation using anti-CBP IgG conjugated to protein A-Sepharose, demonstrated the formation of a lutein-rCBP complex. Sequence analyses coupled with binding specificity suggest that CBP is a new member of the StAR protein family that binds carotenoids rather than cholesterol.

Surface properties of γ-alumina deposits on highly permeable cellular carriers

The electron–acceptor properties and the hydroxyl cover of the surface of a secondary support, γ-Al2O3 deposited on highly porous permeable cellular materials of corundum and Nichrome, were studied. The effect of lanthana additives on the acid–base properties of the surface of this support was also studied. The surface properties of the secondary support are typical of γ-Al2O3. The type of highly permeable porous cellular materials used and the modifying additives influence both the acidity of hydroxyl groups and the strength and concentration of electron-acceptor sites.

The Antitrust Implications of Capacity Reallocation by a Dominant Firm

When a firm acquires rival firms in one market, and moves their capacity to another market, should antitrust authorities be concerned? We address this question by studying a multi‐stage game. A dominant firm has the opportunity to acquire fringe firms that operate in the same market. Then, the dominant firm has the opportunity to move capacity from that market to a second market. The model is motivated by a series of acquisitions in the Specialized Mobile Radio industry aimed at establishing a new cellular carrier. We derive necessary and sufficient conditions for the dominant firm to acquire too little capacity relative to the social optimum. The results shed light on the Consent Decree negotiated in US v. Motorola Inc. and Nextel Communications Inc., 1994.

Cellular security: better, but foes still lurk

Service providers have largely solved the cellular phone cloning problem through application of technology, but it has been replaced by other problems: subscription fraud (the same problem that bedevils issuers of credit cards) and the misapplication of service provider subsidies on handsets. Subscription fraud has several forms: pretending to be another, real person; pretending to be a nonexistent person; and even just being yourself and pretending you intend to pay your bill. Subsidy fraud involves taking a phone whose cost has been heavily subsidized by a cellular carrier and activating it on a different carrier's network. Solutions to these problems exist. As the practice of conducting serious business over the Internet continues to grow, other security issues will arise. In particular someone conducting business on a cell phone needs to be confident of the identity of the other instrument's user. The technical solutions discussed, like RF fingerprinting and authentication, do a good job of guaranteeing that the handset is what it claims to be, but they guarantee nothing about the person using it. Several approaches are being pursued to user identification.

Aliphatic α,γ-bis(Amides) of Methotrexate. Influence of Chain Length on In-vitro Activity Against Sensitive and Resistant Tumour Cells

The synthesis of short-chain alkyl bis(amides) (heptyl-, isoheptyl-, octyl-) and nonylamide derivatives as lipophilic derivatives of methotrexate is reported. Direct amine substitution on methotrexate diethyl ester and a carbodiimide-assisted coupling method were used. The compounds were screened for in-vitro inhibitory activity against bovine liver dihydrofolate reductase and growth inhibition of human lymphoblastoid methotrexate-sensitive and resistant CCRF-CEM cells and erythroleukaemic K562 cells. The lipophilic methotrexate derivatives, despite showing lower activity against methotrexate-sensitive tumour cell lines, maintained similar activity to methotrexate, even against a methotrexate-transport resistant cell subline, since they can penetrate tumour cells by a passive route, by-passing the deficient cellular carrier system for the folates. Increasing the lipophilicity of methotrexate is a possible strategy to overcome the clinical resistance to the drug by tumour cells.

Billing strategies and performance analysis for PCS networks

It is predicted that by the year 2000, US cellular carriers will invest billions of dollars for cellular billing and customer care. Two of the most desirable attributes of the cellular billing systems are the flexibility of upgrade and the ability to inform the billing experts quickly about the status of the system to minimize any possible fraud and improve customer service. Although the second attribute can be realized by reporting the billing customer record in real time, this tends to congest the signaling channel, which is not desirable. We propose several schemes for the provision of a quick billing status report which maintains low-signaling traffic. The performance of these schemes is derived analytically. We expect that these results may provide a guideline for the future design of on-line billing systems in personal communication services (PCSs) networks.

Pharmacokinetics of melphalan in isolated limb perfusion.

The pharmacokinetics of melphalan was studied by sampling of tissue and plasma in 72 rats that underwent isolated hyperthermic limb perfusion under different conditions. A miniaturized extracorporeal circulation system for small animals was used for perfusion of the rat hindlimb. Melphalan levels (L-phenylalanine mustard, L-PAM) were determined by high-performance liquid chromatography (HPLC). The temperature of the perfusate plasma and tissue, pH, administration method, and flow rate were modified and compared with regard to their influence on pharmacokinetic parameters. The highest tissue penetration of melphalan was observed under the following conditions: (a) pH range of the perfusate plasma between 7.3 and 7.7 (physiological environment), (b) temperature range of the perfusate from 40 degrees to 41.5 degrees C (destruction of cellular carrier systems at higher temperatures and increased inactivation by hydrolysis of melphalan above 41.5 degrees C), (c) application of melphalan as a single dose into the reservoir of the extracorporeal circuit (optimal tissue penetration), and (d) reduced perfusate flow (prolonged contact time between perfusate and tissue).

The arabidopsis thaliana AGRAVITROPIC 1 gene encodes a component of the polar-auxin-transport efflux carrier.

Auxins are plant hormones that mediate many aspects of plant growth and development. In higher plants, auxins are polarly transported from sites of synthesis in the shoot apex to their sites of action in the basal regions of shoots and in roots. Polar auxin transport is an important aspect of auxin functions and is mediated by cellular influx and efflux carriers. Little is known about the molecular identity of its regulatory component, the efflux carrier [Estelle, M. (1996) Current Biol. 6, 1589-1591]. Here we show that mutations in the Arabidopsis thaliana AGRAVITROPIC 1 (AGR1) gene involved in root gravitropism confer increased root-growth sensitivity to auxin and decreased sensitivity to ethylene and an auxin transport inhibitor, and cause retention of exogenously added auxin in root tip cells. We used positional cloning to show that AGR1 encodes a putative transmembrane protein whose amino acid sequence shares homologies with bacterial transporters. When expressed in Saccharomyces cerevisiae, AGR1 promotes an increased efflux of radiolabeled IAA from the cells and confers increased resistance to fluoro-IAA, a toxic IAA-derived compound. AGR1 transcripts were localized to the root distal elongation zone, a region undergoing a curvature response upon gravistimulation. We have identified several AGR1-related genes in Arabidopsis, suggesting a global role of this gene family in the control of auxin-regulated growth and developmental processes.

Control of photosystem formation in Rhodobacter sphaeroides.

Rhodobacter sphaeroides has the capacity to grow by aerobic and anaerobic respiration and photosynthetically in the light under anaerobic conditions, as well as fermentatively. It can fix atmospheric nitrogen and carbon dioxide. It resembles other gram-negative members of the class Proteobacteria when growing aerobically, but a reduction in oxygen tension induces an intracellular differentiation of the inner membrane, leading to the formation of the intracytoplasmic membrane system (ICM). The ICM houses the integral membrane pigment-protein complexes constituting the photosystem (PS), comprised of the reaction center (RC) and two light-harvesting (LH) complexes. For an early review of ICM biosynthesis, see reference 44. The LH complexes are designated B800-850 (LHII) and B875 (LHI), based on their respective absorption maxima. The ratio of LHI to RC is fixed at approximately 15:1, whereas the ratio of LHII to the LHI-RC unit is variable, changing in a manner inverse to the incident light intensity. These three pigment-protein complexes are the spectral complexes (SC) of the R. sphaeroides PS. Detailed structural information about these complexes in several species of Rhodobacter is emerging (72). The LH complexes capture light energy and direct that energy to the RC, where conversion of the excitation energy takes place and is intrinsically coupled with a cyclic flow of electrons, ultimately to the periplasmically localized cytochrome c2, which serves to rereduce the RC to allow a new cycle of electron flow (for further details, see references 42, 44, and 72). Bacteriochlorophyll (Bchl) absorbs most of the light energy within the SCs and is critical to the assembly and final structure of the SCs (44, 84, 87). The carotenoids (Crt) have a minor role in absorbing light energy (15), but they function to protect the complexes against photo-oxidative damage, dissipate excess radiant energy, and help to maintain the structure and relative abundance of each SC (35, 50, 53). A reduction in oxygen tension is both necessary and sufficient to induce synthesis of the ICM (reviewed in references 42 and 44), which is gratuitously produced under anaerobic dark growth conditions, in the presence of an alternate electron acceptor such as dimethyl sulfoxide (DMSO). Oxygen tension is the major environmental stimulus controlling PS induction, with variations in light intensity determining the cellular level of the ICM and the abundance of the different SCs. PS formation is tightly regulated, with checkpoints at all levels of information flow, from transcriptional through posttranslational. In the following sections, we will describe what we currently know about the regulatory processes controlling the formation and abundance of SCs in R. sphaeroides. We will present a working model for the regulation of PS formation in R. sphaeroides 2.4.1 which is based on the critical role of cellular redox carriers. For clarity, we will, throughout this review, define aerobic growth as that which occurs under highly oxygenic conditions, under which there are no detectable SCs present in wild-type membranes.

Congestion relief on power-controlled CDMA networks

A digital cellular radio code-division multiple-access (CDMA) system can only support a finite number of users before the interference plus noise power density, I/sub 0/, received at the cellular base station causes an unacceptable frame-error rate. Once the maximum interference level is reached, new arrivals should be blocked. In a power-controlled CDMA system, the base station can direct mobiles to reduce their power and data rate to reduce interference and allow more users on the system. This approach is employed in TIA IS-95 with respect to the time-varying voice activity on cellular voice channels. We investigate an alternative technique where we adjust the power and data rate of mobile data users to the time-varying interference level to allow more users on a congested system. This scheme was simulated for various proportions of voice and data users and offered traffic levels. Blocking probabilities are reduced in some cases by two orders of magnitude. Message wait time, now a random variable, may exceed the wait time for a constant rate system at high traffic levels. If the cellular carrier has a maximum blocking requirement, an adaptive rate/power system can increase the capacity. For example, a base station that normally supports 26.4 Erlangs offered traffic with 2% blocking can support 33.5 Erlangs with the same blocking probability if adaptive rates and power control are used. Thus, the adaptive rate system can increase the capacity by 27%.

Effects of inhibitors of enzymatic and cellular pH-regulating systems on central sympathetic chemosensitivity.

Previous studies in cats using isolated NaCl-CO2 perfusion of the lower brainstem demonstrated an intrinsic chemosensitivity of sympathoexcitatory bulbospinal neurones within the rostroventrolateral medulla (RVLM). In the present experiments, the effects of inhibitors of enzymatic and cellular systems, known to be involved in pH regulation, were investigated. Isolated perfusion of the lower brainstem with CO2-enriched solutions was performed and preganglionic sympathetic nerve activity (SNA) was recorded. Drugs were locally injected into the left RVLM with glass micropipettes. Perfusion of the RVLM with CO2-enriched solutions over a period of 15 s induced a marked increase in SNA. The magnitude of absolute changes in SNA during perfusion depended on the level of basal SNA before perfusion. Microinjections of 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and acetazolamide (ACZ) induced a marked rise in basal SNA, whereas diethylpyrocarbonate (DEPC) and ethylisopropylamiloride (EIPA) had no significant effect on basal SNA. After application of DIDS and DEPC, the peak change in SNA due to perfusion of the RVLM with CO2-enriched solutions was slightly diminished. Furthermore, neither ACZ nor EIPA produced any significant influence on the slope, peak change and time course of the increase in SNA compared with control perfusions. We conclude that the enzymatic and cellular carrier systems tested in this study are not or only slightly involved in central sympathetic chemosensitivity.

Lack of requirement for sterol carrier protein-2 in the intracellular trafficking of lysosomal cholesterol.

Previous work has established that the absence of peroxisomes, as occurs in Zellweger syndrome, is accompanied by the absence of cellular sterol carrier protein-2 (SCP2). In the present study, Zellweger-syndrome fibroblasts and peroxisome-deficient CHO-ZR78 cells were used to study the role of SCP2 in the intracellular transport of low density lipoprotein (LDL)-derived lysosomal cholesterol. By immunoblotting, peroxisome-deficient cells were confirmed to contain either no detectable SCP2 or far less SCP2 than corresponding normal cells. To monitor the transport of lysosomal cholesterol to the plasma membrane, we measured efflux of lysosomal cholesterol to HDL3 or phospholipid vesicles. SCP2-deficient cells, in comparison to normal cells, demonstrated little or no impairment in this efflux, suggesting that SCP2 is not required for the efficient delivery of lysosomal cholesterol to the plasma membrane. To examine the role of SCP2 in the delivery of lysosomal cholesterol to acyl-CoA:cholesterol acyltransferase (ACAT) in the rough endoplasmic reticulum (RER), the lysosomal and whole-cell cholesterol pools were differentially labeled, and then the ACAT-mediated esterification of each pool was measured in response to an 8-h incubation with native LDL. For both cholesterol pools, esterification was stimulated by LDL, and the responses in normal and Zellweger cells were similar, demonstrating that SCP2 is required for neither the stimulation of ACAT that follows LDL uptake nor for the transport of lysosomal cholesterol to the RER. These findings suggest that some major aspects of lysosomal cholesterol trafficking in cells can occur by mechanisms not involving SCP2.

Gene therapy for neurologic disease.

Gene therapy is a potentially potent new method of treating a number of neurologic disorders previously considered refractory to current conventional therapeutic treatments. Numerous advances have been made in the construction of expression vectors, cellular and viral transgene carriers, and the characterization of target cells for neuronal gene therapy. Two primary approaches to nervous system gene transfer have emerged as a result of these advances. The in vivo approach concentrates on direct transfer of genetic material to cells in vivo using viral and chemical agents. The ex vivo approach relies on genetic transfer to cultured cells that are subsequently implanted into a host organism. Both of these methods have been used in preliminary experiments designed to test the efficacy of gene transfer strategies in the amelioration of nervous system dysfunction.

Institutional reform in Sri Lanka's telecommunication system: Regulation, corporatization, and competition∗

Sri Lanka's telecommunication system has undergone major institutional reform in the past 12 years. This article describes the three phases of the reform process—a prologue stretching from 1980 to around 1984, an abortive effort to privatize the Department of Telecommunications in 1984–89, and a third, less radical but successful, stage of institutional reform from 1991 onward. The reforms are analysed in terms of changes in forms of regulation, corporate organization, and industrial organization. The dramatic change from a system with one all‐encompassing, unregulated, government‐owned telecommunication monopoly to one with three cellular carriers, two data carriers, and five paging services, and experimenting with Build‐Operate‐Transfer schemes for basic telephony is documented. The interplay of domestic and external factors in these changes are examined, as are the interplay of factors internal and external to the telecommunication system. The broad implications of the reforms, including impact on grou...