Small Sag Research Articles

Straightening of the Northern San Jacinto Fault, California, as Seen in the Fault-Structure Evolution of the San Jacinto Valley Stepover

Abstract We investigate a releasing stepover between the Casa Loma and Claremont strands of the northern San Jacinto fault zone to evaluate the late Quaternary structural evolution of the fault zone, and to assess the likelihood of a rupture jumping across the stepover. Our new cone penetration test (CPT) and trench observations along the Claremont fault at Mystic Lake indicate that the main strand of the Claremont fault has jumped nearly a half kilometer westward into the San Jacinto releasing stepover during the late Quaternary. Multiple faults are inferred from the CPT data within a small sag at the northeast side of the stepover that cuts through younger stratigraphy to the west of the basin‐bounding fault near Mystic Lake. Previous seismic‐reflection data also suggest the presence of a young fault that cuts basin strata beneath the middle of Mystic Lake farther west of our study area. Numerous tectono‐geomorphic features observed in satellite and Light Detection and Ranging Digital Elevation Model (LiDAR DEM) imagery are interpreted to delineate the location of the currently active faults, including a zone of faults that cut across the basin from the northern end of the Casa Loma fault to the Claremont fault. Seismicity observations suggest the presence of many faults within the stepover zone. Finally, new paleoseismic data from the Mystic Lake site suggest that some late Holocene earthquakes may have jumped the stepover. All of these observations suggest that the San Jacinto stepover, which has been used as the primary basis for segmenting the northern San Jacinto fault zone, is being bypassed and that the fault zone may now be capable of larger earthquakes than previously expected.

Numerical and experimental dynamic analysis and control of a cable stayed bridge under parametric excitation

In cable-stayed bridges, the occurrence of parametric excitation is very probable due to the presence of many low frequencies in the deck or tower and in the stay cables. When a local (cable) and a global (structure) mode are coupled, even very small motion of the deck or tower may cause dynamic instability and extremely large vibration amplitudes of the stay cables. This paper presents a nonlinear dynamic study of a three dimensional cable stayed bridge in construction phase under parametric excitation. A nonlinear inclined cable with small sag which takes into account the quadratic and cubic nonlinear couplings between in-plane and out-of-plane motion, is coupled with a finite element model of a cable stayed bridge. Active damping is successfully added to the structure using collocated displacement actuator–force sensor pairs located on each cable and a robust control strategy based on decentralized collocated Integral Force Feedback. The effect of the amplitude of excitation as well as the added active damping on the steady state response of the stay cable under parametric excitation is studied numerically and experimentally. A phenomenon of energy transfer between the cable and the deck is observed. The experimental results are qualitatively in good agreement with the numerical ones.

Increased Size and Stability of CA1 and CA3 Place Fields in HCN1 Knockout Mice

Hippocampal CA1 and CA3 pyramidal neuron place cells encode the spatial location of an animal through localized firing patterns called "place fields." To explore the mechanisms that control place cell firing and their relationship to spatial memory, we studied mice with enhanced spatial memory resulting from forebrain-specific knockout of the HCN1 hyperpolarization-activated cation channel. HCN1 is strongly expressed in CA1 neurons and in entorhinal cortex grid cells, which provide spatial information to the hippocampus. Both CA1 and CA3 place fields were larger but more stable in the knockout mice, with the effect greater in CA1 than CA3. As HCN1 is only weakly expressed in CA3 place cells, their altered activity likely reflects loss of HCN1 in grid cells. The more pronounced changes in CA1 likely reflect the intrinsic contribution of HCN1. The enhanced place field stability may underlie the effect of HCN1 deletion to facilitate spatial learning and memory.

Occurrence of shallow gas in the easternmost Lago Fagnano (Tierra del Fuego)

ABSTRACTHigh‐resolution seismic profiles acquired in the eastern sector of Lago Fagnano, the southernmost ice‐free lake in the world, have shown the presence of very shallow gas‐bearing layers in the upper sedimentary sequences. The gas‐related features observed on seismic profiles include a typical, very strong reflection with reversed polarity, multiple reflections and acoustic blanking that hide subsurface sedimentary and structural features. The top of the acoustically high‐amplitude layer is located between 0.3–1.7 m below the lake floor. It generally forms a sharp boundary, often marked by a varying offset probably due to different levels of gas penetration, which could be related to the lithology of the overlying sediments. To confirm the presence of gas, some gravity cores were recovered in places where the blanking effect was most relevant and in the supposed gas‐free zone. Sediment core analyses have highlighted the occurrence of significant organic‐rich components within the uppermost, largely unconsolidated sedimentary layers, in correspondence of the seismically‐detected gassy zone, whereas only a few organic layers were found in the gas‐free zone. We assume that the main origin of gas is linked to the presence of a shallow, thin peat‐rich layer of Middle‐Late Holocene age. In fact, the mapped gassy zone occurs in correspondence of the outlet of the Rio Turbio, the principal tributary of Lago Fagnano, which discharges waters coming from a relatively small sag pond located immediately to the east of the eastern shore of the lake. To date, this is the first evidence of shallow gas in Tierra del Fuego lakes.

Nonlinear Finite Element Analysis of Beam String Structure

Beam string structure (BSS), which is a new kind of semi-rigid hybrid system, composed of arch, strut and string, has been developed rapidly in long-span steel structures in recent years. Based on the principle of virtual work and Updated Lagrange, the formulas of geometric nonlinear F.E.M. for spatial beam element, cable element and truss element are derived respectively in this paper. Taking the one-way BSS model of the steel roof in Guangzhou International Convention and Exhibition Center as a computational example by using both linear and nonlinear analysis method, the analytical results show that it is appropriate when adopting the straight truss element with two joints and equivalent elastic modulus to simulate the cable element with small sag. Although the linear analysis can meet the requirement of practical engineering due to its weak nonlinearity of BSS, the nonlinear method is also important to improve the precision theoretically. The conclusions obtained may be helpful for the designers in similar projects.

Influence of the Tension Variety on Non-Linear Natural Frequency of an Inclined Cable

According to the vibration characteristics of small sag cable, an equation of non-linear free transverse in-plane vibration of an inclined cable is presented considering the effects of the flexural rigidity. In the equation the influence of the tension variety along the inclined cable was taken into account by using the precise parabola equation of the taut cable. Taking single mode of a cable in consideration, the governing equation was simplified as a traditional Duffing equation with a quadratic term. It was solved by using the method of Fourier series. Combined with engineering practice, an example was provided to study nonlinear natural vibration characteristic of an inclined cable in plane when the length, the inclination angle, the tension were changed separately, whether considering the influence of tension variety along the inclined cable or not.

Small-molecule modulators of the Sonic Hedgehog signaling pathway

Sonic hedgehog (Shh) is the most widely characterized of the three vertebrate Hedgehog homologs, and is essential for proper embryonic development. Shh binds to its receptor, Patched (Ptch1), resulting in the de-repression of Smoothened (Smo). This leads to the activation of Gli2, which regulates the transcription of target genes that include Gli1 and Ptch1. Several synthetic and naturally occurring small-molecule modulators of Smo have been discovered. Shh-signaling antagonists that bind to Smo include cyclopamine, SANT1, and Cur-61414. Shh signaling agonists that bind to Smo include the synthetic small molecules purmorphamine and SAG. Small molecules that inhibit Shh signaling downstream of Smo, GANT58 and GANT61 have also been reported. Robotnikinin inhibits the Shh pathway by directly targeting Shh. Although progress has been made in understanding and modulating Shh signaling, fundamental aspects of Shh signal transduction remain obscure, including the mechanism(s) whereby Ptch1 regulates Smo activity. Small-molecule modulators of Shh signaling provide a means to regulate the activity of a pathway implicated in medulloblastoma, basal cell carcinoma (BCC), pancreatic cancer, prostate cancer and developmental disorders. Several Shh inhibitors have not succeeded in the clinic for unknown reasons, but clinical trials in BCC and pancreatic cancer with the promising Smo antagonists GDC-0449 and IPI-926 are currently underway.

Integrated high-performance thousand-metre scale cable-stayed bridge with hybrid FRP cables

To overcome the limitations of conventional steel stay cables in a thousand-meter scale cable-stayed bridge, hybrid basalt and carbon (B/C) FRP cables were investigated to achieve integrated high performances in the bridge of this scale as a replacement for steel cables. First, the material properties of different cables were discussed, and static and dynamic analyses on the entire bridges with different cables were conducted by means of finite element method. Moreover, the aerodynamic stability of different cables was studied in terms of the Scruton number. Results show that (1) hybrid B/CFRP with a 28% volume proportion of carbon fibres exhibits relatively high stiffness, economical cost, a small sag effect and sufficient fatigue resistance, which was proven suitable for stay cables; (2) based on the stiffness principle, the cable-stayed bridge with hybrid B/CFRP cables exhibits linear L–D behaviour and higher stiffness compared to the bridge with steel cables under the static load, and this advantage would become more apparent with the elongation of span; (3) the hybrid B/CFRP cable processes much higher natural frequencies than steel cables, which could lower the possibility of resonance between stay cables and the bridge deck. Furthermore, the aerodynamic stability of hybrid B/CFRP cables is superior to other cables due to its designable inherent damping.

Internal Resonance of Coupled Non-planar Vibrations of an Axially Moving Cable with Small Sag

Internal Resonance of Coupled Non-planar Vibrations of an Axially Moving Cable with Small Sag

Modelling comminution patterns within a pilot scale AG/SAG mill

The patterns of rock comminution within tumbling mills, as well as the nature of forces, are of significant practical importance. Discrete element modelling (DEM) has been used to analyse the pattern of specific energy applied to rock, in terms of spatial distribution within a pilot AG/SAG mill. We also analysed in some detail the nature of the forces, which may result in rock comminution. In order to examine the distribution of energy applied within the mill, the DEM models were compared with measured particle mass losses, in small scale AG and SAG mill experiments. The intensity of contact stresses was estimated using the Hertz theory of elastic contacts. The results indicate that in the case of the AG mill, the highest intensity stresses and strains are likely to occur deep within the charge, and close to the base. This effect is probably more pronounced for large AG mills. In the SAG mill case, the impacts of the steel balls on the surface of the charge are likely to be the most potent. In both cases, the spatial pattern of medium-to-high energy collisions is affected by the rotational speed of the mill. Based on an assumed damage threshold for rock, in terms of specific energy introduced per single collision, the spatial pattern of productive collisions within each charge was estimated and compared with rates of mass loss. We also investigated the nature of the comminution process within AG vs. SAG mill, in order to explain the observed differences in energy utilisation efficiency, between two types of milling. All experiments were performed using a laboratory scale mill of 1.19 m diameter and 0.31 m length, equipped with 14 square section lifters of height 40 mm.

Experimental study of stray fields of elastically and inelastically bent steel tubes with hinged ends

The tangential and normal components of the stray field of ferromagnetic steel tubes were measured. The distribution of magnetization (averaged over the cross section of the tubes) under elastic and inelastic bending of the tubes in a small geomagnetic field with a small sag increment was determined for tubes with hinged ends. It was shown that the sizes of inelastically deformed regions (IDR), hardening zones in these IDRs (in the presence of high deflections), and mean first-order internal stress σ0 can be found by measuring the stray field.

Wavelet-Galerkin method for the free vibrations of an elastic cable carrying an attached mass

A multilevel representation of Daubechies compactly supported wavelet has been used to study the free vibrations of elastic catenary cables carrying an attached mass. Anti-derivatives of wavelets are used to guarantee satisfaction of boundary conditions. Natural frequencies, mode shapes and dynamic tensions are obtained and compared with the classical Fourier series representation. The localization feature of wavelets has been implemented to enter the singularity region that is produced by the attached mass. More wavelets are used near the mass location and the spurious oscillations in the solution are minimized with few number of terms in the series. However, the Fourier solution shows many oscillations along the cable length and Gibbs phenomenon at the mass location. In both methods, reverting and swapping modes are discovered in which higher modes revert to lower modes and that the horizontal displacement components become greater than the vertical ones even for cables with small sag to span ratios.

Nonlinear dynamic response and active vibration control of the viscoelastic cable with small sag

The problem considered is an initially stressed viscoelastic cable with small sag. The cable material is assumed to be constituted by the hereditary differential type. The partial differential equations of motion is derived first. Then by applying Galerkin's method, the governing equations are reduced to a set of third order nonlinear ordinary differential equations which are solved by Runge-Kutta numerical integration procedures. Only after the transverse vibration of the plane is considered and the nonlinear terms are neglected, can the nonlinear ordinary differential equations be expressed as a continuous state equation in the state space. The matrix of state transition is approximated stepwise by the matrix exponential; in addition, the state equation is discretized to a difference equation to improve the computing efficiency. Furthermore, an optimal control of procedure system based on the minimization of a quadratic performance index for state vector and control forces is developed. Finally, the effect of dynamic response of the cable, which is produced by viscoelastic parameters, is testified by the research of digital simulation.

The vibrations of an extensible flexible thread with a small sag

The free vibrations of an extensible flexible thread with a small sag are considered. A new form of solution of the equations of equilibrium of an extensible flexible thread is obtained. The differential equations of small vibrations about the equilibrium position are derived. An asymptotic analysis of the vibrations out of the vertical plane is carried out. It is established that these vibrations are close to the vibrations of a string. An asymptotic analysis of the low-frequency and high-frequency vibrations in the vertical plane is carried out. It is established that the natural frequencies and forms of the low-frequency vibrations depend very much on two small parameters: the parameter ε, characterizing the sag value, and the parameter δ, characterizing the degree of the thread stretching. It is proved that the low-frequency transverse vibrations when ε 2/δ « 1 are also to the vibrations of a string, and when ε 2/δ a ̊ 1 they are close to vibrations of an inextensible thread. If the quantities ε 2 and δ have the same asymptotic order, the most representative asymptotic form is obtained. In the high-frequency region there are long-wave longitudinal and short-wave transverse vibrations, irrespective of the ratio of the two small parameters. More complex forms of vibrations also sometimes arise, characterized by interaction between the longitudinal and transverse motions. Asymptotic expansions, which are uniformly valid over the whole frequency range, are obtained.

ACTIVE TENDON CONTROL OF CABLE-STAYED BRIDGES

This paper considers the active vibration control of cables and cable/structure systems with an active tendon controlling the axial displacement of the cable anchor point. It is demonstrated that a force feedback based on a collocated force sensor measuring the tension in the cable is feasible and that this control configuration can be associated with control laws with guaranteed stability properties. Experimental results are presented on a cable with small sag and on a cable/structure system. They show that the control algorithm can provide the structure with several percent of active damping and that the parametric resonance does not occur when the natural frequency of the structure is twice that of the cable.

The use of data from small-scale mills and computer simulation techniques for scale-up and design of SAG mill circuits

This paper describes the work done in a 0.69 m diameter wet continuous SAG mill and with various simulation models to predict the performance of full-scale SAG mills. The use of such small diameter mills has been the subject of controversy among various authors. There are, however, several advantages offered by testing on a smaller scale, making it attractive to pursue this line of investigation. These are: lower sample requirements, ability to use drill core to test ore variability, and ease in emptying the mill to monitor changes in its content under different operating conditions. The ore used for these tests amounted to no more than 500 kg per test series. Comparisons made with full-scale SAG mills showed very good agreement in the areas of net specific energy consumption and the product size distribution. The use of 80 mm balls and a feed top size ranging from 80 to 125 mm appear necessary to achieve this agreement. All the characteristics of full-scale SAG mills were reproduced in the small SAG mill, and were easily measured. Predictions made by different simulation programmes were compared. A conclusion drawn from the work is that small-scale SAG mills can be used to accurately design SAG mill circuits, provided that the ball size and feed size of the samples used is large enough. Scale-up can be done directly from the results using familiar formulae. Simulation can enhance the value of the results and be very useful in testing a number of options. The approach is advantageous equally to scale-up for small operations, where large samples may not be available for pilot-plant testing, and for design of large scale milling circuits, where overdesign could lead to major cost penalties.

A NON-LINEAR DYNAMIC MODEL FOR CABLES AND ITS APPLICATION TO A CABLE-STRUCTURE SYSTEM

A set of governing equations for dynamic transverse motions of a cable with small sag is firstly obtained where effects of finite motions of the cable and small support motions are included. Cable motions are separated into two parts; quasi-static motions and modal motions. The quasi-static motions are the displacements of the cable which moves as an elastic tendon due to the support movements. The modal motions are expressed as a combination of the linear undamped modes of a cable with fixed ends. By Lagrange's equations of motion, the governing equations of the non-linear cable motions are obtained, where quadratic as well as cubic non-linear couplings appear. The cable model developed is next applied to a cable–structure system. A global/local mode approach is employed; the total motions are expressed in terms of global and local motions. The local motions are the modal motions of the cable, while the global motions are 3-D motions of the structure which include quasi-static motions of the cables only. The global are expressed as a combination of the eigenmodes computed by 3-D FEM in which cables are treated as tendons. By using Lagrange's formulation, algebraic governing equations are finally obtained in which global–local interaction appears as linear and quadratic couplings. The model for the system is modified to include the actuator motions at the cable supports; the actuator motions are in the cable axis direction. The study shows many possibilities for the control of global and/or local modes.

Estimation Curve for Modal Damping in Stay Cables with Viscous Damper

To simplify the procedure of designing viscous dampers for stay cables in bridges, a universal estimation curve is proposed that relates the modal damping ratio of the cable with attached damper, the mode number, the damper size, the damper location, and three parameters of the cable: span, mass per unit length, and fundamental frequency. The curve is obtained from numerical complex‐eigenvalue analysis of a taut cable with a single damper near the anchorage, with judicious grouping of these parameters into nondimensional factors. Several numerical examples illustrate the convenient use of this design aid, as well as show realistic values of the required damper size and location and the expected additional damping in the first few modes. The damping to be attained is usually high enough to suppress most vibrations induced by wind. However it is noted that a small sag of the cable and slight nonviscous properties of the damper may reduce the damper effectiveness. A modified design curve may have to incorpor...

The elastic frequencies of cables

It is shown that the elastic modes of cables can be different from those of taut strings. For certain values of the physical parameters frequency coalescence or the so-called phenomenon of frequency avoidance is observed, accompanied by substantial changes in the mode shapes. An asymptotic solution is used to explore in detail the properties of the elastic modes of horizontal and inclined cables of small sag to span ratio.

The dynamics of translating cables

The dynamics of a translating catenary are studied. The static and linearized dynamic governing equations are derived along the local tangential and normal directions and it is shown that in this form two simpler equations can be derived and solved asymptotically for both small and large sag cables, horizontal or inclined. For small sag cables the solutions of one of the asymptotic equations undergo fundamental changes for specific values of the elastic stiffness, inclination angle, sag-to-span ratio and speed of translation resulting in strong mode interactions. For horizontal cables this explains the phenomena of frequency coalescence and mode reversion [1], as well as the frequency crossover and modal changes of non-translating cables [2]. For inclined cables frequency coalescence never occurs, while mode reversion is partial and strongly dependent on the inclination angle. However, in all cases of mode interaction the dynamic tension is greatly amplified. For large sag cables the solution accounts for the significant tension and curvature variation. The solution reduces to previous results for non-translating cables horizontal [3, 4] or inclined [5].