A pseudo-polynomial algorithm for optimal capacitor placement on electric power distribution networks

Allocation of shunt capacitor banks on radial electric power distribution networks allow reduction of energy losses and aggregated benefits. Four decades ago Durán proposed the use of dynamic programming to find optimal capacitor placement on these networks; however, with the restricting assumption of single-ended networks, which precluded its application to real capacitor allocation problems. Subsequently heuristic methods prevailed in the capacitor allocation literature. Here the Extended Dynamic Programming Approach (EDP) lifts Durán’s restricting assumption; a richer definition of state and the projection of multidimensional informations into equivalent one-dimensional representations are the supporting concepts. In addition to allow consideration of multi-ended networks, EDP deals with other requirements of capacitor allocation studies, including the use of both fixed and switched capacitors and representation of voltage drops along the networks. When switched capacitors are considered the optimization procedure also solves the capacitor control problem, obtaining the best tap adjustments for them. Case studies with real scale distribution networks put into perspective the benefits of the methodology; EDP has the appeal of providing global optimal solutions with pseudo-polynomial computational complexity in the worst-case, and with linear complexity for practical applications.     

Urinary peptides as a diagnostic tool for renal failure detected by matrix-assisted laser desorption/ionisation mass spectrometry: an evaluation of their clinical significance

The development of new analytical methodologies related to the proteome for the evaluation of renal physiology and pathology is surely of wide interest for physicians, giving them new tools for monitoring complications associated with diabetes, such as end-stage renal disease. In the present study, the clinical significance of the urinary abundance of two peptides, SGSVIDQSRVLNLGPITR (the uromodulin precursor, m/z 1912) and IGPHypGPHypGLMGPP [present in the collagen-α-5(IV) chain precursor, m/z 1219], detected by matrix- assisted laser desorption/ionisation mass spectrometry (MALDI/MS) in microalbuminuric or nephropathic diabetic patients and in non-diabetic nephropathic patients was evaluated. A progressive increase in the abundance of the ion at m/z 1219 and a decrease in the abundance of the ion at m/z 1912 have been found in diabetic microalbuminuric, diabetic-nephropathic and nephropathic patients. Linear correlations are present between serum creatinine values and the abundances of the ions at m/z 1219 (positive correlation, r=0.3645, P<0.0001) and at m/z 1912 (negative correlation, r=-0.3053, P<0.0005). Correlations between the MALDI data and the estimated glomerular filtration rate were also found, while relationships with urinary albumin excretion were found only in sub-sets of patients. Analysis of receiver operating characteristic curves showed a sensitivity up to 96% and a specificity of up to 84% for the two ionic species, or their ratio, for distinguishing diabetic patients with different degrees of nephropathy from healthy subjects, proving that the urinary abundance of the two peptides at m/z 1219 and m/z 1912, determined with MALDI/MS, may be considered as a possible diagnostic tool for the determination of progression toward renal failure, also with the aim of monitoring kidney function, in diabetic patients.     

Molecular dynamics of host-guest complexes of small gas molecules with calix[4]arenes

The unexpected sorption of gases by a low-density p-tert-butylcalix[4]arene crystal polymorph raises fundamental questions about differential gas transport and sequestration in the organic solid state. To gain insight into the processes underlying these observations, we have used molecular dynamics simulations, augmented with calculations of potentials of mean force, to investigate the stability of isolated host-guest complexes and the relationship between the dynamics of these complexes and the dynamics of a solvated host molecule. Thermal fluctuations of the calixarenes themselves are found to be consistent with proposed mechanisms for gas entry into the host cavities, while relative host-guest stabilities correlate well with experimental absorption-desorption isotherms in some cases (CO2 and CH4) but not in others (C2H2). In these isolated systems, stable complexes characteristically form when the attractive interactions of the guest with the ring of negative charge density on the inner surface of the host cavity are not disrupted by thermal motion. The experimentally observed efficient uptake of gases such as C2H2 by the host crystals suggests, however, that stabilization of host-guest complexes in some systems may derive from dynamical constraints imposed by the crystal lattice.     

Gravitation in Hertz Mechanics

In a previous paper, one of us presented an axiomatic framework for non-relativistic classical particle mechanics where the concept of force is not assumed as a primitive notion. Such a formulation was inspired by Hertz's mechanics, which considers only three primitive concepts: time, space, and mass. It is also emphasized that there is only one Fundamental Law: Every free system persists in its state of rest or of iniform motion in a straightest path. In the present paper we formulate a theory of gravitation which seems to be compatible with Hertz's mechanics, in the sense that it makes no explicit reference to the concepts of force or actions-at-a-distance. We show how to derive Kepler's Laws in our axiomatic framework.     

Electron wave packet dynamics in twisted nonlinear ladders with correlated disorder

Within a tight-binding Hamiltonian approach, we study the dynamics of one-electron wave packets in a twisted ladder geometry with adiabatic electron-phonon interaction. The electron-phonon coupling is taken into account in the time-dependent Schrödinger equation through a cubic nonlinearity. This physical scenario incorporates several relevant ingredients to study the electronic wave packet dynamics in DNA-like segments. In the absence of nonlinearity, a random sequence of nucleotides pairs makes the wave packets remain localized, according to the standard picture of the Anderson localization. However, when the electron-phonon interaction is turned on, Anderson localization is suppressed and a subdiffusive regime takes place. Further, we show that the wave packet trapping can be controlled by an external field perpendicular to the helicity axis of the double-strand chain.     

Random fiber laser

We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (TiO2) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher.     

Single-design-parameter microstructured optical fiber for chromatic dispersion tailoring and evanescent field enhancement

A microstructured optical fiber with a single design parameter is proposed and demonstrated. In such a structure three thin, long glass webs join in the fiber center, forming its core. By changing the web thickness it is possible to tune the zero-dispersion wavelength from approximately 0.7 to >2.0 microm while keeping a tiny core area and single-mode guidance. Supercontinuum generation is shown in a silica fiber with a web thickness of 850 nm. The small core area and the massive hole area also make the structure very attractive for the sensing and study of fluids.