Optimal scheduling of handoffs in cellular networks

The phenomenon of hard handoffs (as applicable to FDMA- and TDMA-based networks) as well as soft handoffs (as applicable to DS/CDMA-based networks) is formulated as stochastic optimization problems. The signals received by a mobile user are treated as stochastic processes with associated rewards, which are functions of some measurable characteristics of the received signals, while the handoff is associated with a switching penalty. This formulation captures the trade-offs involved in handoffs in a flexible manner and captures many facets of popular cellular communication systems in use currently. Using dynamic programming, necessary and sufficient conditions for determining the optimal base station(s) the mobile should be associated with during each decision epoch are derived. For the cases where the above-mentioned necessary and sufficient conditions fail to determine an optimal decision, “limited lookahead” arguments are used for determining handoff decisions. The decisions are taken in a decentralized manner, which makes its implementation easier compared to centralized algorithms. Simulation results show that for the hard handoffs, performance gain by the proposed algorithm over the simpler threshold algorithms proposed in the literature is small; however, for the case of soft handoffs, the proposed algorithm offers considerable improvement over the algorithm proposed in the IS-95 standard     

Validation of an MPC Polymer Coating to Attenuate Surface‐Induced Crosstalk between the Complement and Coagulation Systems in Whole Blood in In Vitro and In Vivo Models

Artificial surfaces that come into contact with blood induce an immediate activation of the cascade systems of the blood, leading to a thrombotic and/or inflammatory response that can eventually cause damage to the biomaterial or the patient, or to both. Heparin coating has been used to improve hemocompatibility, and another approach is 2‐methacryloyloxyethyl phosphorylcholine (MPC)‐based polymer coatings. Here, the aim is to evaluate the hemocompatibility of MPC polymer coating by studying the interactions with coagulation and complement systems using human blood in vitro model and pig in vivo model. The stability of the coatings is investigated in vitro and MPC polymer‐coated catheters are tested in vivo by insertion into the external jugular vein of pigs to monitor the catheters' antithrombotic properties. There is no significant activation of platelets or of the coagulation and complement systems in the MPC polymer‐coated one, which was superior in hemocompatibility to non‐coated matrix surfaces. The protective effect of the MPC polymer coat does not decline after incubation in human plasma for up to 2 weeks. With MPC polymer‐coated catheters, it is possible to easily draw blood from pig for 4 days in contrast to the case for non‐coated catheters, in which substantial clotting is seen.     

Possible role of dentin matrix in region-specific deposition of cellular and acellular extrinsic fibre cementum

The mechanism whereby a region-specific deposition of the two types of cementum (cellular cementum and acellular extrinsic fibre cementum) is regulated on the growing root surface was tested using bisphosphonate-affected teeth of young rats and guinea pigs. The animals were injected subcutaneously with 8 or 10 mg P x kg body weight(-1) x day(-1) of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) for 1 or 2 weeks. In rat molars, HEBP prevented mineralization of newly formed root dentin matrix and totally inhibited de novo deposition of acellular extrinsic fibre cementum. Instead, thick cellular cementum was induced on the non-mineralized root dentin surface, irrespective of the position of the root. In both animals, cellular cementum was also induced on the non-mineralized surface of root analogue dentin in HEBP-affected incisors, where only acellular extrinsic fibre cementum is deposited under normal conditions. In normal rat molars, dentin sialoprotein (DSP) was concentrated along the dentin-cellular cementum border, but not that of dentin and acellular extrinsic fibre cementum. In HEBP-affected rat incisors, DSP was shown to penetrate through the non-mineralized dentin into the surrounding tissues, but not through the mineralized portions. These data suggest that, at the site of cellular cementum formation, putative inducing factors for cellular cementum might diffuse into the periodontal space through the newly deposited mantle dentin matrix before it is mineralized. At earlier stages of root formation, mantle dentin might mineralize more promptly not to allow such diffusion. The timing of mineralization of mantle dentin matrix might be the key determinant of the types of the cementum deposited on the growing root surface.     

Direct demodulation of a 10.6µm FM signal with an NH2D stark cell

A new technique for direct demodulation of a 10.6-μm FM signal using a Stark absorption cell is described. A Stark tunable absorption line in NH2D is used to track the time-varying frequency of the incoming FM laser signal using a closed servo loop. The demodulated FM signal is proportional to the feedback voltage applied to the Stark cell. Demodulation at frequencies up to 5 kHz has been demonstrated, the rate being limited only by the bandwidth of the available servo electronics.     

Stark-induced three-wave mixing in molecular gases--Part II: Experiment

The first observation of resonantly enhanced, dc-induced, three-wave mixing in a gas is presented. A CW CO2laser beam and microwave radiation at 4 GHz are mixed in a microwave Stark cell containing gaseous NH2D. A single new sideband, 4 GHz below the applied CO2laser frequency, is observed with the aid of a scanning Fabry-Perot interferometer. The dependence of the sideband signal on gas pressure, microwave frequency, applied dc field, and microwave power are presented and compared with theoretical predictions.     

Resonantly enhanced 26 GHz parametric upconversion of CO2laser in NH3

Resonantly enhanced three-wave mixing of the 10.784 μmR(18) line of the C¹³O2¹⁶laser and microwave radiation at 26.378 GHz in Stark tunable N¹⁴H3has resulted in upconverted parametric output at 10.774 μm. The energy levels of N¹⁴H3involved in the interaction and the apparatus used in the experiment are described. Experimental results showing saturation of the parametric signal with increasing N¹⁴H3pressure, input microwave power, and input laser power are described.     

Fiber Optical Intensity Sensors

Fiber optical intensity sensors are made of optical fibers connected to a miniaturized optical sensor which is based on either a mechanical light valve, a light scattering process, a photoemission or photoabsorption process, or the transmission property of the optical fiber itself. Use of the optical fiber to transmit light to and from the optical sensor makes it possible to construct an electrically passive sensor with remotely located electronic readout capability. Major advantages of this type of sensors are electromagnetic interference immunity, electrical passiveness and safety, miniature size, and ruggedness, In this paper, the large variety of fiber optical intensity sensors reported to date will be classified by their sensing mechanism. Examples will be given for each category of sensors with reported performances.     

Intrusion-alarmed fiber optic communication link using a planarwaveguide bimodal launcher

This paper summarizes the results of our study of a point-to-point, intrusion-alarmed, graded-index, multimode optical fiber communication system. In this intrusion-alarmed system, data light is transmitted in the lowest order modes of a graded-index multimode fiber and intrusion alarm monitor light is simultaneously transmitted in high-order modes. An attempted intrusion to extract data light by bending the fiber results in attenuation of the monitor light in high-order modes, thereby sounding an alarm at the receiver. However, the data light in the fundamental mode, or in the lowest order modes, propagates along or near the fiber axis where the refractive index is highest and is exceptionally difficult to extract from the fiber. Even for severe bending of the fiber, light in the lowest order modes remains trapped in a set of lowest order modes. Additional benefits of data light transmitted in the lowest order modes are capabilities for wider bandwidths and lower modal noise. The performance of four fabricated planar waveguide bimodal launchers for simultaneously launching data light into the fundamental mode, or into the lowest order modes, and monitor fight into high-order modes of graded-index multimode fiber is described. The configuration, construction, and performance of a laboratory prototype alarmed system are described     

Angular division multiplexer for fiber communication using graded-index rod lenses

An angular division multiplexer which uses graded-index (GRIN) rod lenses and a spatial modal filter (SMF) is described. Angular division multiplexing (ADM) uses selective excitation of mode groups " to multiplex signals in a transmission fiber. The GRIN-rod lenses collimate the input beams from two input fibers. The SMF selects particular mode groups from each input to be imaged on the transmission fiber. Design and construction of the device are described. Experimental results show that each signal is well confined to its designated mode groups. Crosstalk results are adequate for digital data transmission.     

Cell Surface Functionalization with Heparin-Conjugated Lipid to Suppress Blood Activation

Organ transplantation leads to damage of the endothelial glycocalyx of the transplanted organ, and the activated endothelial surface induces thromboinflammation. The result is dysfunction of the transplanted organ, known as ischemia reperfusion injury (IRI). Long-term graft survival strongly depends on the regulation of IRI. Here the aim is to reconstruct the glycocalyx to regulate blood activation during IRI. Heparin-conjugated lipid (fHep-lipid) is synthesized with 0.6, 1.8, 2.7, 4.5, or 8.0 fragmented heparins per lipid to compare their anticoagulation activity. First, liposome and cells are modified with each fHep-lipid and the surface properties are evaluated. Then the hemocompatibility of the modified human mesenchymal stem cells (hMSCs) is examined in a loop model using human blood. The antithrombin-binding capacity and anti-factor Xa activity of the fHep-lipids depend on the number of conjugated heparins, with efficacy increasing with increasing number of heparins. The modified liposomes are highly negatively charged and show strong anti-factor Xa activity. In addition, the cell surfaces of human erythrocytes and hMSCs can be uniformly modified with fHep-lipid. The whole blood studies reveal that fHep-lipid on hMSCs can prevent generation of thrombin–antithrombin complexes, coagulation markers, and platelet aggregation, whereas unmodified hMSCs trigger activation of the platelet and coagulation systems.