H∞ Control for Externally Excited Building Structures with Active Mass Damper under Actuator Saturation

This paper investigates the application of active mass dampers to mitigate the vibrations of building structures subjected to unknown external excitations under controller saturation conditions. By utilizing an H∞ control strategy, the optimal state feedback controller is derived by solving the linear matrix inequality problem for controller saturation. Case studies show that the proposed controller is capable of stabilizing the closed-loop system with good control performance and effectively suppressing vibrations in building structures under unknown external excitation. When compared to controllers that do not consider saturation, the proposed controller requires lower gain and results in reduced energy consumption. The research findings provide valuable insights for addressing real-world building structure control problems, contributing to both theoretical significance and practical applications.

Model Reduction Methods for High-Rise Buildings with Active Mass Damper Control Systems

To improve the performance of an active mass damper control system,the controller should be designed based on a reduced-order model. An improved method based on balanced truncation method was proposed to reduce the dimension of high-rise buildings,and was compared with other widely used reduction methods by using a framework with ten floors. This optimized method has improvement of reduction process and choice of the order. Based on the reduced-order model obtained by the improved method and pole-assignment algorithm,a controller was designed. Finally,a comparative analysis of structural responses,transfer functions,and poles was conducted on an actual high-rise building. The results show the effectiveness of the improved method.

Seismic response of controlled structures with active multiple tuned mass dampers

Active multiple tuned mass dampers （referred to as AMTMD）, which consist of several active tuned mass dampers （ATMDs） with identical stiffness and damping coefficients but varying mass and control force, have recently been proposed to suppress undesirable oscillations of structures under ground acceleration. It has been shown that the AMTMD can remarkably improve the performance of multiple tuned mass dampers （MTMDs） and is also more effective in reducing structure oscillation than single ATMDs. Notwithstanding this, good performance of AMTMD （including a single ATMD illustrated from frequency-domain analysis） may not necessarily translate into a good seismic reduction behavior in the time-domain. To investigate these phenomena, a three-story steel structure model controlled by AMTMD with three ATMDs was implemented in SIMULINK and subjected to several historical earthquakes. Likewise, the structure under consideration was assumed to have uncertainty of stiffness, such as 4-15% of its initial stiffness, in the numerical simulations. The optimum design parameters of the AMTMD were obtained in the frequency-domain by implementing the minimization of the minimum values of the maximum dynamic magnification factors （DMF） of general structures with AMTMD. For comparison purposes, response analysis of the same structure with a single ATMD was also performed. The numerical analysis and comparison show that the AMTMD generally renders better effectiveness when compared with a single ATMD for structures subjected to historical earthquakes. In particular, the AMTMD can improve the effectiveness of a single ATMD for a structure with an uncertainty of stiffness of 4-15% of its initial stiffness.

Facile fabrication of ultrafine nickel-iridium alloy nanoparticles/graphene hybrid with enhanced mass activity and stability for overall water splitting

Developing active and durable electrocatalysts for overall water splitting is desirable but challenging to realize sustainable hydrogen production.Here,we report a facile and general method to prepare ultrafine nickel(Ni)-iridium(Ir)alloy nanoparticles/graphene hybrids for overall water splitting.The optimized hybrid with 4.9 wt%Ir exhibits much higher catalytic activity and durability than commercial 20 wt%Ir/C for both oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).Theoretical simulations reveal that the incorporation of Ir in metallic Ni lattice regulates hydrogen adsorption free energy to the optimum level,thus improving HER activity,while in situ generated amorphous Ir-Ni hydr(oxy)oxides around metallic Ni-Ir core have been demonstrated to be the active species under OER conditions,which switches OER rate-determining step to energy-favorable pathway.The overall water splitting electrolyzer assembled by the optimized electrocatalyst shows a low cell voltage of only 1.52 V and excellent stability to deliver a current density of 10 m A cm-2.This work provides a powerful strategy toward general synthesis of ultrafine alloy nanoparticles for high-performance overall water splitting.

Why are halo coronal mass ejections faster?

Halo coronal mass ejections （CMEs） have been to be significantly faster than normal CMEs, which is a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that clearly display loopshaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in white-light intensity. Then, we perform a Monte Carlo simulation of 20000 artificial limb CMEs that have an average velocity of ～523km s -1. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light inten-sity of many slow CMEs becomes remarkably reduced when they turn from being viewed as a limb event to being viewed as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of ＂detectable＂ halo CMEs is ～922km s -1, very close to the observed value. This also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and some of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.

Flux emergence in the solar active region NOAA 11158: the evolution of net current

We present a detailed investigation of the evolution of observed net vertical current using a time series of vector magnetograms of the active region （AR） NOAA 11158 obtained from the Helioseismic and Magnetic Imager. We also discuss the relation of net current to the observed eruptive events. The AR evolved from the βγ to βγδ3 configuration over a period of six days. The AR had two sub-regions of activity with opposite chirality： one dominated by sunspot rotation producing a strong CME, and the other showing large shear motions producing a strong flare. The net current in each polarity over the CME producing sub-region increased to a maximum and then decreased when the sunspots were separated. The time profile of net current in this sub-region followed the time profile of the rotation rate of the south-polarity sunspot in the same sub-region. The net current in the flaring sub-region showed a sudden increase at the time of the strong flare and remained unchanged until the end of the observation, while the sunspots maintained their close proximity. The systematic evo- lution of the observed net current is seen to follow the time evolution of total length of strongly sheared polarity inversion lines in both of the sub-regions. The observed photospheric net current could be explained as an inevitable product of the emergence of a twisted flux rope, from a higher pressure confinement below the photosphere into the lower pressure environment of the photosphere.

Periodicity in the most violent solar eruptions: recent observations of coronal mass ejections and flares revisited

Using the Hilbert-Huang Transform method, we investigate the periodic- ity in the monthly occurrence numbers and monthly mean energy of coronal mass ejections （CMEs） observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliographic Observatory from 1999 March to 2009 December. We also investigate the periodicity in the monthly occurrence numbers of Hα flares and monthly mean flare indices from 1996 January to 2008 December. The results show the following. （1） The period of 5.66 yr is found to be statistically significant in the monthly occurrence numbers of CMEs; the period of 10.5 yr is found to be statistically significant in the monthly mean energy of CMEs. （2） The periods of 3.05 and 8.70 yr are found to be statistically significant in the monthly occurrence numbers of Hα flares; the period of 9.14 yr is found to be statistically significant in the monthly mean flare indices.

DOUBLE LOOP ACTIVE VIBRATION CONTROL OF PNEUMATIC ISOLATOR WITH TWO SEPARATE CHAMBERS

A newly designed pneumatic spring with two separate chambers is promoted and double-loop active control is introduced to overcome the following drawbacks of passive pneumatic isolation： ① The low frequency resonances introduced into the system; ② Conflict between lower isolation frequency and stiffness high enough to limit quasi-static stroke;③ Inconsistent isolation level with different force load. The design of two separate chambers is for the purpose of tuning support frequency and force independently and each chamber is controlled by a different valve. The inner one of double-loop structure is pressure control, and in order to obtain good performance, nonlinearities compensation and motion flow rate compensation （MFRC） are added besides the basic cascade compensation, and the influence of tube length is studied. The outer loop has two functions： one is to eliminate the resonance caused by isolation support and to broaden the isolation frequency band by payload velocity feedback and base velocity feed forward, and the other is to tune support force and support stiffness simultaneously and independently, which means the support force will have no effect on support stiffness. Theoretical analysis and experiment results show that the three drawbacks are overcome simultaneously.

CONTINUITY AND BREAK OF CHATTER VIBRATION STATUS

By turning a specifically designed conical part, complete process of metal cutting, in which the chatter occurs and expands, is recorded and analyzed. This process exposes that chatter vibration has two characters called continuity and break. The continuity character means that vibration extent enlarges continuously while chatter frequency is almost changeless as the cutting depth extends downwards continuously. The break one is that chatter frequency moves rapidly downwards to a lower level while chatter remains after the cutting depth reach another given value. It is confirmed through an exciting test that the two chatter frequencies obtained in chatter test belong to the natural frequencies of workpiece system and cutting tool system respectively. From the viewpoints of chatter energy supplying and chatter mass effect, the. chatter should occur on one of the two final executive components in its natural frequency. On this basis, a new chatter model with two chatter active bodies is proposed. This new model can better explain the above phenomenon, and adapt to chatter monitoring and improvement of component structure well.

Trends in gravity changes from 2009 to 2013 derived from ground-based gravimetry and GRACE data in North China

North China is a key region for studying geophysical progress. In this study, ground-based and Gravity Recovery and Climate Experiment（GRACE） gravity data from 2009 to 2013 are used to calculate the gravity change rate（GCR） using the polynomial fitting method. In general, the study area was divided into the Shanxi rift, Jing-Jin-Ji（Beijing-Tianjin-Hebei Province）, and Bohai Bay Basin（BBB） regions. Results of the distribution of the GCR determined from ground-based gravimetry show that the GCR appears to be ＂negativepositive-negative＂ from west to east, which indicates that different geophysical mechanisms are involved in the tectonic activities of these regions. However, GRACE solutions are conducted over a larger spatial scale and are able to show a difference between southern and northern areas and a mass redistribution of land water storage.

Application of annexation principle to the study of thermodynamic properties of Ag-Bi-In metallic melts

Based on the measured activities, the phase diagrams and the annexation principle, the calculating models of mass action concentrations for Ag-Bi and Ag-Bi-In melts have been formulated. The calculated results agree with practice and obey the mass action law, showing that the models formulated can reflect the structural characteristics of both melts. Meanwhile, it confirms that annexation principle is applicable to the Ag-Bi-In metallic melts. The melts involving eulectic which give rise to phase separation, and in which activities exhibit positive deviation from Raoult's law is the basic cause of melts transforming from homogeneous to heterogeneous ones.

The Filament Eruption of 1999 March 21 and Its Associated Coronal Dimmings and CME

We report a filament eruption near the center of the solar disk on 1999 March 21, in multi-wavelength observations by the Yohkoh Soft X-Ray Telescope （SXT）, the Extremeultraviolet Images Telescope （EIT） and the Michelson Doppler Imager （MDI） on the Solar and Heliospheric Observatory （SOHO）. The eruption involved in the disappearance of an Ha filament can be clearly identified in EIT 195A difference images. Two flare-like EUV ribbons and two obvious coronal dimming regions were formed. The two dimming regions had a similar appearance in lines formed in temperature range 6×10^4 K to several 10^6 K. They were located in regions of opposite magnetic polarities near the two ends of the eruptive filament. No significant X-ray or Hα flare was recorded associated with the eruption and no obvious photospheric magnetic activity was detected around the eruptive region, and particularly below the coronal dimming regions. The above surface activities were closely associated with a partial halo-type coronal mass ejection （CME） observed by the Large Angle and Spectrometric Coronagraphs （LASCO） on the SOHO. In terms of the magnetic flux rope model of CMEs, we explained these multiple observations as an integral process of largescale rearrangement of coronal magnetic field initiated by the filament eruption, in which the dimming regions marked the evacuated feet of the flux rope.

Increased utilization and mass activity of PtRu on reduced graphene oxide by heat treatment of its aerogel followed by composite with nanomaterials

The method to increase PtRu utilization and its catalytic activity of PtRu nanoparticles supported on reduced graphene oxide(RGO)by avoiding its restacking was proposed with the aim of developing an active catalyst for a direct methanol fuel cell.The heat treatment at 200◦C of the GO aerogel(GOA)prepared by freeze drying of GO ice was introduced to weaken the attractive force of the hydrogen bonding between the GO sheets followed by the composite with the nanoparticles,i.e.,ketjenblack(KB),TiO_(2)and Ti_(4)O_(7),at different weight ratios.The catalyst supported on the heat-treated GOA(RGOA),PtRu/RGOA,improved the PtRu utilization to some extent and also increased the ECSA and mass activity compared to that of PtRu/RGO.RGOA had fewer oxygen functional groups,especially the epoxy groups.Due to the treatment and composite,the PtRu utilization was increased from 66.5%for PtRu/RGO to 128.6%for PtRu/RGOA+Ti_(4)O_(7)(4:1)and the mass activity was improved from 50.7 A/g-PtRu for PtRu/RGO to 130.5 A/g-PtRu for PtRu/RGOA+Ti_(4)O_(7)(1:1).The Ti_(4)O_(7)nanoparticles showed the best catalytic performance for the composite suggesting that the strong interaction between Ti_(4)O_(7)and the Pt nanoparticles was effective due to its high electronic conductivity.

Fishbone-like platinum-nickel nanowires as an efficient electrocatalyst for methanol oxidation

Platinum(Pt)-based electrocatalyst with low Pt content and high electrocatalytic performance is highly desired in fuel cell applications.Herein,we demonstrated that platinum-nickel(Pt-Ni)nanowires with an average composition of PtNi3 and a fishbone structure can be readily synthesized and used as an efficient electrocatalyst toward methanol oxidation reaction(MOR).The PtNi3 fishbone-like nanowires(PtNi3-FBNWs)present features such as richer Pt on the surface than in the bulk,high-index facets on the rough surface,and polyhedral facets at the ends of side chains.Such compositional and structural features could be determinative to the enhanced performance in the electrocatalysis of MOR.Compared with commercial 20%Pt/carbon black(Pt/C),the specific activity and mass activity of the PtNi3-FBNWs are enhanced by approximately 4.76 and 3.02 times,respectively.The stability of electrocatalysis is significantly improved as well.Such comprehensive enhancement indicates that the PtNi3-FBNWs would be a promising candidate toward MOR in fuel cells.