Instability Line Research Articles

CIRCULAÇÃO DE BRISA FLUVIAL E A BANDA DE PRECIPITAÇÃO NA MARGEM LESTE DA BAÍA DE MARAJÓ

The precipitation in Belem region is mainly due the large atmospheric systems such as ITCZ and mesoscale systems like the Instability Lines. Beside these systems, there are convective systems forced locally which also promote precipitation in this region. This paper studies a convective system, observed for first time during the campaign of the RAIN project, which is called Micro Instability Line Fluvial (MLF) because its formation is associated with river breeze circulation. The GOES 12 satellite data, radar band X, anemometer, rain gauges, disdrometer, and NCEP reanalyzes were used to study this MLF. High-resolution numerical simulation with the BRAMS model was made for this MLF, using two grids with horizontal resolution of 3 km and 1 km. The simulation results showed that the MLF was formed by river breeze from the Marajo Bay, causing precipitation since the early stages in Belem area until this MLF was on the west bank of the Marajo bay. During its propagation westward, this MLF had increased its intensity, which was maximum over the Bay of Marajo, where there is intense transportation of cargo and passengers, and shipwrecks are the most frequent type of accidents.

Laminoplasty for the Treatment of Cervical Myelopathy. 5 Year Experience at University Clinic Colombia

Introduction Cervical myelopathy affects primarily elderly people, caused mainly by a degenerative process of spondylosis in which both static (disc, ligament ossification, congenital stenosis, tumors) and dynamic (flexion-extension of cervical spine adaptive changes, nervous fiber elasticity, ischemia, trauma) factors that lead to the compression and diminished blood supply of the spine cord. The symptoms can range from mild paresthesias according to the compromised cervical level, gait disturbances, pain to as severe as paraplegia, with a natural history of chronic progression, Surgical treatment of this entity include anterior or posterior decompression with arthrodesis and laminoplasty. In this study we aim to report the result obtained with Cervical Laminoplasty described by O'brien during de years 2010 to 2015. Material and Methods An observational retrospective descriptive study was performed, reviewing the clinical records from preop to postop of patients with cervical myelopathy, Functional information was gathered using the scale of the Japanese Orthopaedic Association and Pain Analog Visual Scale. X-rays were evaluated measuring canal diameter, Chiba's line, Pavlov index and signs of instability. MRI studies were used to measure canal diameter in the axial plane and to identify signs of myelopathy. Inclusion criteria were patients older than 18 years, that had both clinical and image diagnosis for cervical myelopathy in which the O'brien laminoplasty was performed Results 10 patients with an average age of 74 (64 to 84yrs) completed follow up according to our inclusion criteria. AVS improved from 7 to 3. The JOA Scale showed improvement in all the patients from 10 to 14 in the global score, which corresponds to a progression from a Functional class II to I. Images evaluation showed widening of the cervical canal as seen with a 0.76 Pavlov index preop to 0.96 postop and a 33% widening in the MRI sagittal view. Conclusion For the management of cervical myelopathy, proper documentation of the pathology both clinical and images allows to decide the adequate management of the patient. The O'brien technique for cervical laminoplasty proved to be an effective alternative in the treatment of this entity.

Rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory

We construct sequences of rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory, employing two equations of state for the nuclear matter. We analyze the dependence of the physical properties of these neutron stars on the Gauss-Bonnet coupling strength. For a given equation of state we determine the physically relevant domain of rapidly rotating neutron stars, which is delimited by the set of neutron stars rotating at the Kepler limit, the set of neutron stars along the secular instability line, and the set of static neutron stars. As compared to Einstein gravity, the presence of the Gauss-Bonnet term decreases this domain, leading to lower values for the maximum mass as well as to smaller central densities. The quadrupole moment is decreased by the Gauss-Bonnet term for rapidly rotating neutron stars, while it is increased for slowly rotating neutron stars. The universal relation between the quadrupole moment and the moment of inertia found in General Relativity appears to extend to dilatonic Einstein-Gauss-Bonnet theory with very little dependence on the coupling strength of the Gauss-Bonnet term. The neutron stars carry a small dilaton charge.

Magnetic guidance of the magnetotactic bacterium Magnetospirillum gryphiswaldense.

Magnetospirillum gryphiswaldense is a magnetotactic bacterium with a permanent magnetic moment capable of swimming using two bipolarly located flagella. In their natural environment these bacteria swim along the field lines of the homogeneous geomagnetic field in a typical run and reversal pattern and thereby create non-differentiable trajectories with sharp edges. In the current work we nevertheless achieve stable guidance along curved lines of mechanical instability by using a heterogeneous magnetic field of a garnet film. The successful guidance of the bacteria depends on the right balance between motility and the magnetic moment of the magnetosome chain.

Modeling flow instability of an Algerian sand with the dilatancy rule in CASM

The aim of the present work was the study of instability in a loose sand from Les Dunes beach in Ain Beninan, Algeria, where the Boumerdes earthquake occurred in 2003. This earthquake caused significant structural damages and claimed the lives of many people. Damages caused to infrastructures were strongly related to phenomena of liquefaction. The study was based on the results of two drained and six undrained triaxial tests over a local sand collected in a region where liquefaction occurred. All the tests hereby analyzed followed compression stress-paths in monotonic conditions and the specimens were isotropically consolidated, since the objective was to study the instability due to static loading as part of a more general project, which also included cyclic studies. The instability was modeled with the second-order work increment criterion. The definition of the instability line for Les Dunes sand and its relation with yield surfaces allowed the identification of the region of potential instability and helped in the evaluation of the susceptibility of soils to liquefy under undrained conditions and its modeling. The dilatancy rate was studied in the points where instability began. Some mixed tests were also simulated, starting with drained conditions and then changing to undrained conditions at different time steps.

Saturation Effect on Behaviour of Sandy Soil Under Monotonic and Cyclic Loading: A Laboratory Investigation

This paper presents a laboratory study of the influence of saturation degree on the liquefaction potential of sand. The study is based on drained, undrained monotonic and cyclic triaxial tests. Tests were conducted on a medium dense Hostun RF sand (France) with an initial relative density Dr = 4, 50, 64 and 78 % and the coefficient of Skempton ranging between 0.95 (saturated) and 0.25. For all Skempton’s coefficient B values, the tests were carried out for different loading levels. The monotonic tests show that an increase in the Skempton’s coefficient B leads to a reduction of liquefaction resistance. The decrement of the coefficient of saturation B does not affect the instability and steady state lines. The test results indicate that the liquefaction resistance increases with the decrease of Skempton’s coefficient B. For the high level of loading (RCC = 0.5), the number required to cause liquefaction varied little with the Skempton’s coefficient B (Nc = 9, 10 and 11 for B = 0.67, 0.36 and 0.25 respectively). For the low level (RCC < 0.40), the number of cycles needed for liquefaction increases susceptibly with the reduction of the coefficient of Skempton (B). A simple mathematical relation has been suggested to correlate the liquefaction resistance with the coefficient of Skempton B.

Fast rotating neutron stars with realistic nuclear matter equation of state

We construct equilibrium configurations of uniformly rotating neutron stars for selected relativistic mean-field nuclear matter equations of state (EOS). We compute in particular the gravitational mass ($M$), equatorial ($R_{\rm eq}$) and polar ($R_{\rm pol}$) radii, eccentricity, angular momentum ($J$), moment of inertia ($I$) and quadrupole moment ($M_2$) of neutron stars stable against mass-shedding and secular axisymmetric instability. By constructing the constant frequency sequence $f=716$ Hz of the fastest observed pulsar, PSR J1748-2446ad, and constraining it to be within the stability region, we obtain a lower mass bound for the pulsar, $M_{\rm min}=[1.2$-$1.4] M_\odot$, for the EOS employed. Moreover we give a fitting formula relating the baryonic mass ($M_b$) and gravitational mass of non-rotating neutron stars, $M_b/M_\odot=M/M_\odot+(13/200)(M/M_\odot)^2$ [or $M/M_\odot=M_b/M_\odot-(1/20)(M_b/M_\odot)^2$], which is independent on the EOS. We also obtain a fitting formula, although not EOS independent, relating the gravitational mass and the angular momentum of neutron stars along the secular axisymmetric instability line for each EOS. We compute the maximum value of the dimensionless angular momentum, $a/M\equiv c J/(G M^2)$ (or "Kerr parameter"), $(a/M)_{\rm max}\approx 0.7$, found to be also independent on the EOS. We compare and contrast then the quadrupole moment of rotating neutron stars with the one predicted by the Kerr exterior solution for the same values of mass and angular momentum. Finally we show that, although the mass quadrupole moment of realistic neutron stars never reaches the Kerr value, the latter is closely approached from above at the maximum mass value, as physically expected from the no-hair theorem. In particular the stiffer the EOS is, the closer the Kerr solution is approached.

Refining the phase diagram of Pb1−xLax(Zr0.9Ti0.1)1−x/4O3 ceramics by structural, dielectric, and anelastic spectroscopy investigations

We present the results of dielectric and anelastic spectroscopy measurements, together with X-ray diffraction investigations, which allow us to establish more precisely the phase diagram of Pb1−xLax(Zr0.9Ti0.1)1−x/4O3 (PLZT x/90/10) in the compositional range around the AFE/FE phase boundary (0 &amp;lt; x &amp;lt; 0.04). From structural analysis and polarization-electric field measurements, we have found that the ground state of PLZT samples with x &amp;lt; 0.025 is rhombohedral R3c, while samples with x &amp;gt; 0.032 are antiferroelectric with orthorhombic Pbam structure. In-between, for compositions with 0.025 ≤ x ≤ 0.032, a coexistence of the AFE/FE phases is evidenced. The use of complementary dielectric and anelastic techniques allows to follow the phase transitions shifts throughout all the interesting composition range and to construct the temperature-composition phase diagram. The tilt instability line, separating the R3c and R3m low and high temperature phases, has been evidenced. Moreover, the new transition, associated with the onset of disordered tilting preceding the long range order of the R3c phase, previously found in Zr-rich Pb(Zr,Ti)O3, is confirmed in rhombohedral PLZT x/90/10 compositions.

On the cosmic evolution of the specific star formation rate

The apparent correlation between the specific star formation rate (sSFR) and total stellar mass (M_star) of galaxies is a fundamental relationship indicating how they formed their stellar populations. To attempt to understand this relation, we hypothesize that the relation and its evolution is regulated by the increase in the stellar and gas mass surface density in galaxies with redshift, which is itself governed by the angular momentum of the accreted gas, the amount of available gas, and by self-regulation of star formation. With our model, we can reproduce the specific SFR-M_star relations at z~1-2 by assuming gas fractions and gas mass surface densities similar to those observed for z=1-2 galaxies. We further argue that it is the increasing angular momentum with cosmic time that causes a decrease in the surface density of accreted gas. The gas mass surface densities in galaxies are controlled by the centrifugal support (i.e., angular momentum), and the sSFR is predicted to increase as, sSFR(z)=(1+z)^3/t_H0, as observed (where t_H0 is the Hubble time and no free parameters are necessary). At z>~2, we argue that star formation is self-regulated by high pressures generated by the intense star formation itself. The star formation intensity must be high enough to either balance the hydrostatic pressure (a rather extreme assumption) or to generate high turbulent pressure in the molecular medium which maintains galaxies near the line of instability (i.e. Toomre Q~1). The most important factor is the increase in stellar and gas mass surface density with redshift, which allows distant galaxies to maintain high levels of sSFR. Without a strong feedback from massive stars, such galaxies would likely reach very high sSFR levels, have high star formation efficiencies, and because strong feedback drives outflows, ultimately have an excess of stellar baryons (abridged).

Pre-failure instability of sand under dilatancy rate controlled conditions

Experimental results are presented in this paper to show that a runaway type of pre-failure instability can occur for sand under dilatancy rate controlled conditions when an appropriate strain increment ratio, dεv/dε1, is imposed. This type of instability is similar to the runaway type of instability observed for very loose sand under undrained conditions. Whether a soil element will undergo pre-failure instability depends on the difference between the strain increment ratio of the soil obtained from drained test, under a specified effective confining pressure, (dεv/dε1)s, and the strain increment ratio imposed during the test, (dεv/dε1)i, rather than the absolute magnitude of (dεv/dε1)i. Based on the experimental data obtained in this study it was found that an instability line can be determined from a series of strain path tests conducted at different effective confining pressures but with the same dεv/dε1 by joining the peak points of the effective stress paths to the origin in the q–p′ stress space. This line is similar to the instability line obtained from undrained tests on loose sand. The instability tests under dilatancy rate controlled conditions indicate that the stress ratio at the onset of instability obtained in the instability tests coincide with the peak stress ratio line. This suggests that the peak stress line can be used to predict the onset of instability under dilatancy rate controlled conditions in the same way as the use of instability line to predict the onset of instability under undrained conditions.

Instability of dilative sand

A type of pre-failure instability that occurs for medium loose to dense sand under fully drained conditions is studied in this paper. It is observed experimentally that when a specimen is sheared along a drained stress path involving a decrease in the effective mean stress, it becomes unstable after the stress path crosses an instability line (IL). The IL specifies a minimum stress ratio under which instability may occur. It is not unique but changes with the void ratio of the soil and the applied effective stresses. The instability occurring under drained conditions is different from that under undrained conditions. The differences and similarities between the two types of instability are pointed out. Practical implications of the study in analysing the failure mechanisms of granular soil slopes under various drainage conditions are discussed.

Radar-observed spatial and temporal rainfall variability near the Tapajós-Amazon confluence

Standard Amazonian rainfall climatologies rely on stations preferentially located near river margins. River breeze circulations that tend to suppress afternoon rainfall near the river and enhance it inland are not typically considered when reporting results. Previous studies found surprising nocturnal rainfall maxima near the rivers in some locations. We examine spatial and temporal rainfall variability in the Santarém region of the Tapajós-Amazon confluence, seeking to describe the importance of breeze effects on afternoon precipitation and defining the areal extent of nocturnal rainfall maxima.We used three years of mean S band radar reflectivity from Santarém airport with a Z-R relationship appropriate for tropical convective conditions. These data were complemented by TRMM satellite rainfall estimates. Nocturnal rainfall was enhanced along the Amazon River, consistent with the hypothesis that these are associated with the passage of instability lines, perhaps enhanced by local channeling and by land breeze convergence. In the daytime, two rainfall bands appear in mean results, along the east bank of the Tapajós River and to the south of the Amazon River, respectively.

Role of electron-phonon interaction in a magnetically driven mechanism for superconductivity

We use the renormalization group method to examine the effect of phonon mediated interaction on d-wave superconductivity, as driven by spin fluctuations in a quasi-one-dimensional electron system. The influence of a tight-binding electron-phonon interaction on the spin-density-wave and d-wave superconducting instability lines is calculated for arbitrary temperature, phonon frequency and antinesting of the Fermi surface.The domain of electron-phonon coupling strength where spin-density-wave order becomes unstable against the formation of a bond-order-wave or Peierls state is determined at weak antinesting. We show the existence of a positive isotope effect for spin-density-wave and d-wave superconducting critical temperatures which scales with the antinesting distance from quantum critical point where the two instabilities merge. We single out a low phonon frequency zone where the bond-oder-wave ordering gives rise to triplet f-wave superconductivity under nesting alteration, with both orderings displaying a negative isotope effect. We also study the electron-phonon strengthening of spin fluctuations at the origin of extended quantum criticality in the metallic phase above superconductivity. The impact of our results on quasi-one-dimensional organic conductors like the Bechgaard salts where a Peierls distortion is absent and superconductivity emerges near a spin-density-wave state under pressure is emphasized.

Basic set of experiments for determination of mechanical properties of sand

Abstract A basic set of experiments for the determination of mechanical properties of sands is described. This includes the determination of basic physical and mechanical properties, as conventionally applied in soil mechanics, as well as some additional experiments, which provide further information on mechanical properties of granular soils. These additional experiments allow for determination of steady state and instability lines, stress-strain relations for isotropic loading and pure shearing, and simple cyclic shearing tests. Unconventional oedometric experiments are also presented. Necessary laboratory equipment is described, which includes a triaxial apparatus equipped with local strain gauges, an oedometer capable of measuring lateral stresses and a simple cyclic shearing apparatus. The above experiments provide additional information on soil’s properties, which is useful in studying the following phenomena: pre-failure deformations of sand including cyclic loading compaction, pore-pressure generation and liquefaction, both static and caused by cyclic loadings, the effect of sand initial anisotropy and various instabilities. An important feature of the experiments described is that they make it possible to determine the initial state of sand, defined as either contractive or dilative. Experimental results for the “Gdynia” model sand are shown.

Dipolar Bose gas in a highly anharmonic trap

By means of mean-field theory, we have studied the structure and excitation spectrum of a purely dipolar Bose gas in pancake-shaped trap where the confinement in the x-y plane is provided by a highly anharmonic potential resulting in an almost uniform confinement in the plane. We show that the stable condensates is characterized by marked radially structured density profiles. The stability diagram is calculated by independently varying the strength of the interaction and the trap geometry. By computing the Bogoliubov excitation spectrum near the instability line we show that soft "angular" rotons are responsible for the collapse of the system. The free expansion of the cloud after the trap is released is also studied by means of time-dependent calculations, showing that a prolate, cigar-shaped condensate is dynamically stabilized during the expansion, which would otherwise collapse. Dipolar condensates rotating with sufficiently high angular velocity show the formation of multiply-quantized giant vortices, while the condensates acquire a ring-shaped form.

The climatic rhythm and blooms of cyanobacteria in a tropical reservoir in São Paulo, Brazil.

The present study sought to develop a methodology to analyse water quality based on the concepts and methods of climate and climatology. Accordingly, we attempted to relate hydro- and limnometeorological techniques and methodologies to a rhythmic analysis technique developed within the context of the Brazilian geographical climatology. Our goal was to assess and analyse cyanobacterial blooms, the main index of water quality for the reservoirs of the "Alto Tietê" Basin and, consequently, the Metropolitan Region of São Paulo, an area of high environmental complexity due to its high degree of development and high population density. The meteorological data used were collected by the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo meteorological station, and the limnological data were collected through the Hydrological Monitoring System implemented by SABESP in the Billings and Guarapiranga Reservoirs and the laboratory of the same entity. The rhythmic and integrated analysis showed that the process of cyanobacterial blooms is dependent on a combination of meteorological factors as temperature and wind intensity that may disrupt the stability of the reservoir, providing the conditions necessary for the development of cyanobacteria during the stabilisation process. The pace of the Atlantic Polar Front Entrance during the winter in São Paulo is a limiting factor for the growth of cyanobacteria because of their high frequency, thus maintaining the balance of the reservoir throughout this period. The weather types those could cause a instability in the water column were: Cold Front entrance (66.67%), conflict between masses (22.22%) and the Tropical Instability Line (11.11%). The possibility for prevention and forecasting periods advise when these reservoirs should not be used, mainly with regard to recreational activities.

Effect of fabric method on instability behavior of granular material

It is well known that the specimen preparation method and the resulting sand fabric significantly affect sand behavior and sand liquefaction resistance. In many cases, the fabric and behavior of reconstituted sand samples do not represent those of in-situ deposits. Therefore, understanding the influence of specimen preparation and sand fabric on its behavior, particularly at the critical state, is important for relating the behavior of laboratory reconstituted specimens to in-situ soil response. In this study, the effect of sand fabric and specimen preparation method on the shearing behavior of sand is studied using triaxial shear tests. Dry funnel pluviation (DFP) and wet tamping (WT) are used to prepare the specimens. The results from instability lines and stress–strain curves indicate that the liquefaction resistance of specimens prepared with the DFP method is more than specimens reconstituted by the WT method.

Cyclic behaviour of loose anisotropically consolidated Ottawa sand under undrained torsional loading

The behaviour of loose, anisotropically consolidated Ottawa sand was examined under undrained cyclic loading in the hollow cylinder apparatus. The stress level, the cyclic stress level and the consolidation stress ratio were varied. The instability line of anisotropically consolidated loose Ottawa sand, defined under monotonic loading, is shown to form a boundary in the vicinity of which a sudden increase in the rate of excess pore water pressure and strain accumulation is observed, and the sand strain-softens. However, this unstable response is arrested at phase transformation, and the sand specimens show a stable or temporarily stable effective stress cycle at low and high consolidation stress ratios respectively. Similar behaviour is observed for isotropically consolidated sand, which exhibits initial liquefaction after strain-softening. The terminal excess pore water pressure associated with this final stage is described as a function of consolidation stress ratio, while the development of excess pore water pressure during cyclic loading is uniquely defined for all tests as a function of normalised shear work. The cyclic resistance of the sand decreases with decreasing consolidation stress ratio. Anisotropic consolidation significantly affects the stiffness and damping ratio values of loose Ottawa sand.

Torsional Shear Behavior of Anisotropically Consolidated Sands

AbstractThis study addresses the effects of anisotropic consolidation on sand behavior by comparing the detailed response of undrained torsional shearing of two sands isotropically and anisotropically consolidated to a range of consolidation stresses and relative densities. Anisotropic consolidation does not appear to alter the mobilized angle of shearing resistance at failure and phase transformation during torsional loading. However, anisotropic consolidation greatly affects the response of the two sands; flow deformation was observed for anisotropically consolidated loose specimens in contrast with limited flow deformation exhibited by their isotropically consolidated counterparts. For the specimens exhibiting brittleness, the instability line is well defined for both isotropically and anisotropically consolidated specimens and it appears to have the same slope in a Mohr-Coulomb diagram independent of the consolidation path followed. However, differences are observed in the peak strength, strength at p...

Effects of coupling between octahedral tilting and polar modes on the phase diagram of the ferroelectric perovskites PbZr1−xTixO3 and (Na1/2Bi1/2)1−xBaxTiO3

Recent anelastic and dielectric spectroscopy measurements revealed new features of the phase diagram of PbZrTiO regarding the manner in which various ferroelectric and octahedral tilt instability lines approach each other. Rather than crossing, they tend to merge, also after considerable bending, and give rise to combined polar/tilt transitions over extended concentration ranges. The same effect is also found in (NaBi)BaTiO. It is proposed that such a behaviour results from cooperative coupling between the polar and tilt modes, and could be explained by a mechanism similar to that proposed by Holakowski in 1973, where coupling of two-order parameters with different symmetries produces a transformation of mixed character. The possible reasons are also discussed why disordered tilting, proposed to occur in correspondence with an elastic stiffening near the antiferroelectric/ferroelectric border in PZT, would be particularly difficult to reveal by diffraction.