The state of the art in beyond 5G distributed massive multiple-input multiple-output communication system solutions.

Beyond fifth generation (5G) communication systems aim towards data rates in the tera bits per second range, with improved and flexible coverage options, introducing many new technological challenges in the fields of network architecture, signal pro- cessing, and radio frequency front-ends. One option is to move towards cell-free, or distributed massive Multiple-Input Multiple-Output (MIMO) network architectures and highly integrated front-end solutions. This paper presents an outlook on be- yond 5G distributed massive MIMO communication systems, the signal processing, characterisation and simulation challenges, and an overview of the state of the art in millimetre wave antennas and electronics.

Near-field intensity pattern at the output of silica-based graded-index multimode fibers under selective excitation with a single-mode fiber.

Selective excitation of graded-index multimode fibers (GI-MMFs) with a single-mode fiber (SMF) has gained increased interest for telecommunication applications. It has been proposed as a way to enhance the transmission bandwidth of GI-MMF links and/or create parallel communication channels over the same GI-MMF. Although the effect of SMF excitation on the transmission bandwidth has been investigated, its impact on the near-field intensity pattern at the output face of the GI-MMF has not been systematically addressed. We have carried out an analysis of the near-field intensity pattern at the output face of silica-based GI-MMFs excited by a radially offset SMF. Simulation results exhibit all of the features displayed by experimental ones. It turns out that differential mode attenuation and delay, full intra-group mode mixing, and small deviations in the refractive index profile of the GI-MMF do not affect the overall shape of the near-field intensity, which is determined by the radial offset of the input SMF. This can be exploited in mode group diversity multiplexing links. The effect of defects in the refractive index profile, such as a central dip or peak, is also examined.

Linear embedding via Green's operators: a modeling technique for finite electromagnetic band-gap structures.

We propose a modular electromagnetic modeling procedure for large finite electromagnetic band-gap (EBG) structures, called linear embedding via Green's operators. It is a diakoptic method based on the Huygens-Schelkunoff principle involving equivalent boundary current sources that electromagnetically characterize the enclosed domain of arbitrary shapes, as if it were a multiport system. In a cascade of embedding steps, separate reusable domains are combined to form larger domains. Device design often involves tuning local medium properties in a compact designated domain with a large environment. Through an additional embedding step the equivalent sources describing the environment can be transferred to the boundary of the designated domain, rendering subsequent design steps very fast. This two-stage optimization process is applied in the design of an EBG power splitter.

Infiltrating spinal angiolipoma: a case report and review of the literature.

Angiolipomas are rarely encountered in the spine. We report the case of a 47-year-old man with a thoracic angiolipoma involving the T9 vertebral body. A preoperative spinal angiogram confirmed a highly vascular neoplasm. The lesion was treated with endovascular embolization prior to a T9 corpectomy and resection of the epidural component of the tumor. At time of surgery, minimal blood loss occurred during resection of the vertebral body and the epidural mass. Pathologic examination demonstrated features consistent with spinal angiolipoma. This report emphasizes the clinical, radiographic, and pathologic features of infiltrating spinal angiolipoma and discusses therapeutic management options.

Studying excited states of proteins by NMR spectroscopy.

Protein structure is inherently dynamic, with function often predicated on excursions from low to higher energy conformations. For example, X-ray studies of a cavity mutant of T4 lysozyme, L99A, show that the cavity is sterically inaccessible to ligand, yet the protein is able to bind substituted benzenes rapidly. We have used novel relaxation dispersion NMR techniques to kinetically and thermodynamically characterize a transition between a highly populated (97%, 25 degrees C) ground state conformation and an excited state that is 2.0 kcal mol(-1) higher in free energy. A temperature-dependent study of the rates of interconversion between ground and excited states allows the separation of the free energy change into enthalpic (Delta H = 7.1 kcal mol(-1)) and entropic (T Delta S = 5.1 kcal mol(-1), 25 degrees C) components. The residues involved cluster about the cavity, providing evidence that the excited state facilitates ligand entry.

Measurement of slow (micros-ms) time scale dynamics in protein side chains by (15)N relaxation dispersion NMR spectroscopy: application to Asn and Gln residues in a cavity mutant of T4 lysozyme.

A new NMR experiment is presented for the measurement of micros-ms time scale dynamics of Asn and Gln side chains in proteins. Exchange contributions to the (15)N line widths of side chain residues are determined via a relaxation dispersion experiment in which the effective nitrogen transverse relaxation rate is measured as a function of the number of refocusing pulses in constant-time, variable spacing CPMG intervals. The evolution of magnetization from scalar couplings and dipole-dipole cross-correlations, which has limited studies of exchange in multi-spin systems in the past, does not affect the extraction of accurate exchange parameters from relaxation profiles of NH(2) groups obtained in the present experiment. The utility of the method is demonstrated with an application to a Leu --> Ala cavity mutant of T4 lysozyme, L99A. It is shown that many of the side chain amide groups of Asn and Gln residues in the C-terminal domain of the protein are affected by a chemical exchange process which may be important in facilitating the rapid binding of hydrophobic ligands to the cavity.

Probing slow time scale dynamics at methyl-containing side chains in proteins by relaxation dispersion NMR measurements: application to methionine residues in a cavity mutant of T4 lysozyme.

A relaxation dispersion-based NMR experiment is presented for the measurement and quantitation of micros-ms dynamic processes at methyl side-chain positions in proteins. The experiment measures the exchange contribution to the 13C line widths of methyl groups using a constant-time CPMG scheme. The effects of cross-correlated spin relaxation between dipole-dipole and dipole-CSA interactions as well as the effects of scalar coupling responsible for mixing of magnetization modes during the course of the experiment have been investigated in detail both theoretically and through simulations. It is shown that the complex relaxation properties of the methyl spin system do not complicate extraction of accurate exchange parameters as long as care is taken to ensure that appropriate magnetization modes are interchanged in the middle of the constant-time CPMG period. An application involving the measurement of relaxation dispersion profiles of methionine residues in a Leu99Ala substitution of T4 lysozyme is presented. All of the methionine residues are sensitive to an exchange event with a rate on the order of 1200 s(-1) at 20 degrees C that may be linked to a process in which hydrophobic ligands are able to rapidly bind to the cavity that is present in this mutant.

Flexibility and ligand exchange in a buried cavity mutant of T4 lysozyme studied by multinuclear NMR.

The Leu99-->Ala mutant of T4 lysozyme contains a large internal cavity in the core of its C-terminal domain that is capable of reversibly binding small hydrophobic compounds. Although the cavity is completely buried, molecules such as benzene or xenon can exchange rapidly in and out. The dynamics of the unliganded protein have been compared to the wild-type protein by measuring the NMR spin relaxation rates of backbone amide and side chain methyl nuclei. Many residues surrounding the cavity were found to be affected by a chemical exchange process with a rate of 1500 +/- 200 s(-1), which is quenched upon addition of saturating amounts of the ligand xenon. The relationship between the structure, dynamics, and energetics of the T4 lysozyme mutant is discussed.

Convulsions induced by centrally administered NMDA in mice: effects of NMDA antagonists, benzodiazepines, minor tranquilizers and anticonvulsants.

1. Convulsions were induced reproducibly by intracerebroventricular injection of N-methyl-D-aspartic acid (NMDA) to conscious mice. 2. Competitive (carboxypiperazine-propylphosphonic acid, CPP; 2-amino-7-phosphonoheptanoic acid, AP7) and non-competitive (MK801; phencyclidine, PCP; thienylcyclohexylpiperidine, TCP; dextrorphan; dextromethorphan) NMDA antagonists prevented NMDA-induced convulsions. 3. Benzodiazepine receptor agonists and partial agonists (triazolam, diazepam, clonazepam, Ro 16-6028), classical anticonvulsants (diphenylhydantoin, phenobarbitone, sodium valproate) and meprobamate were also found to prevent NMDA-induced convulsions. 4. Flumazenil (a benzodiazepine receptor antagonist) and the GABA agonists THIP and muscimol (up to subtoxic doses) were without effect. 5. Flumazenil reversed the anticonvulsant action of diazepam, but not that of MK801. 6. Results obtained in this model differ somewhat from those described in a seizure model with systemic administration of NMDA. An explanation for this discrepancy is offered. 7. This model is a simple test for assessing the in vivo activity of NMDA antagonists and also expands the battery of chemically-induced seizure models for characterizing anticonvulsants not acting at NMDA receptors.