Deformation and strength of cracked member under bending moment and axial force

This paper presents the analysis of the deformation and the strength of a cracked body, emphasizing a superimposed effect of multiple toads on elastic and plastic deformation of an edge-cracked beam or column under two kinds of loads, bending and axial toads. The analysis has been done about the effect of axial force on the elastic angular deformation, including the effect of half-closure of crack, and also on the angular deformation of a cracked plastic hinge. Finally as a practically important example, the above analyses are applied to the problem of the deformation and the load carrying capacity of the cracked column under an eccentric axial force.     

Reaction Mechanisms of Silicon Carbide Fiber Synthesis by Heat Treatment of Polycarbosilane Fibers Cured by Radiation: II, Free Radical Reaction

Silicon carbide (SiC) fibers were synthesized by the pyrolysis of radiation-cured polycarbosilane (PCS) fibers. The pyrolytic reaction was analyzed through free radicals by electron spin resonance (ESR). Free radicals on Si and C atoms were produced in the pyrolysis, and their yield as a function of reaction temperature depended on the oxygen content in the cured PCS fibers. There were two temperature ranges for the reactions related to Si and C atoms in PCS fibers. The radical concentration reflects the rate differences between the radical formation by the cleavage of Si-H and C-H bonds and the decay by recombination of radicals. The reaction of Si-H was strongly influenced by the oxygen content in the cured PCS fibers, and the decay rate of radicals decreased with an increase of the oxygen content in PCS fibers introduced in the curing process.     

Bose-Mesner algebra on finite <Emphasis Type="Italic">G</Emphasis>/<Emphasis Type="Italic">H</Emphasis> coset graphs and its application on continuous time quantum walks

Continuous-time quantum walk (CTQW) over finite group schemes is investigated, where it is shown that some properties of a CTQW over a group scheme defined on a finite group G induces a CTQW over group scheme defined on G/H, where H is a normal subgroup of G with prime index. This reduction can be helpful in analyzing CTQW on underlying graphs of group schemes. Even though this claim is proved for normal subgroups with prime index (using the Clifford’s theorem from representation theory), it is checked in some examples that for other normal subgroups or even non-normal subgroups, the result is also true! Moreover, it is shown that the Bose-Mesner (BM) algebra associated with the group scheme over G is isomorphic to the corresponding BM algebra of the association scheme defined over the coset space G/H up to the scale factor |H|. In fact, we show that the underlying graph defined over group G is a covering space for the quotient graph defined over G/H, so that CTQW over the graph on G, starting from any arbitrary vertex, is isomorphic to the CTQW over the quotient graph on G/H if we take the sum of the amplitudes corresponding to the vertices belonging to the same cosets.     

Surgical and interventional robotics: part III [Tutorial]

Part I of this tutorial described two broad paradigms of interventional assistance: surgical computer-aided design (CAD)/computer-aided manufacturing (CAM) and surgical assistance. Part II focused on the underlying concepts of surgical CAD/CAM, with a particular emphasis on percutaneous procedures. This final installment of our three-part tutorial series discusses surgical assistance. In this section, we introduce the basic concepts of a surgical workstation and briefly review several core robotic technologies used in surgicalworkstations     

Edge density profile variation during a magnetic axis shift in the CHS heliotron/torsatron

Edge density profiles were measured during natural and forced magnetic axis shifts in the lowaspect-ratio heliotron/torsatron CHS, using an 8 keV fast neutral lithium beam probe. The Shafranov shift of the magnetic axis (and hence the dislocation of the LCFS) that was negligible for a low density ECH discharge became substantial (4.5 cm) for a high density NBI discharge (n _e2.5× 10¹³cm^–3) and the corresponding radius of the LCFS increased about 1.2 cm in major radius compared to the vacuum case. For NBI discharges with different settings of the vacuum magnetic axisR _ax (fixed during the discharge), the measured edge density profiles indicated reasonable agreement between the theoretically and experimentally obtained LCFS radii for 90 cm <R _ax<101.6cm, while forR _ax<90 cm the measured radius was 10% larger than expected. When a change ofR _ax from 94.7 cm to 89.9 cm during a discharge was imposed externally, a well behaved plasma boundary moved inward smoothly by about 7.5 cm, while the steepness of the edge density profile changed for different values ofR _ax. The steepest profile was attained forR _ax=92.1 cm when the highest energy content and average density were achieved.     

Laser ion source with a double pulse laser system

To extend an ion beam pulse of a laser ion source, multiple laser shots could be used. To check the feasibility of this idea, we tested double laser irradiations on an iron target. When the interval of the two laser shots is longer than 10 μs, the obtained ion current profile was expressed as a sum of two individual expanded laser plasmas. However, if the interval is too close, a current reduction was observed. This technique can be effectively applied to low charge state ion production.     

Ca–O Binding of Poly[1-carboxylate-2-(N-t- butylcarbamoyl)ethylene-alt-ethylene] and Calcium Carbonate Composites

A novel poly(carboxylate) ligand was synthesized as a ligand for a crystalline CaCO₃-organic composite. Poly[1-carboxylate-2-(N-t-butylcarbamoyl)ethylene-alt-ethylene] has a 7-membered ring with an intramolecular NH·O hydrogen bond between the carboxylate group and the neighboring amide NH proton in the anionic carboxylate form. The configuration of the polymer ligand was estimated with polymer repeat-unit models, (S,S)- or (R,R)-2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,S)- or (R,R)-TBCA) and (S,R)- 2-(N-t-butylcarbamoyl)-cyclohexanecarboxylic acid ((S,R)-TBCA). The proton NMR spectum of the carboxylate anion of (S,S)- or (R,R)-TBCA exhibits a non-hydrogen bonded NH signal at 7.31 ppm in Me₂SO-d ₆. (S,R)-TBCA shows a strongly NH·O hydrogen-bonded NH signal at 8.50 ppm. The observation of one strongly NH·O hydrogen bonded NH signal at 11.3 ppm indicates that the polymer anion has a threo-form in the zigzag polymer main chain. Moreover, a polymer ligand-CaCO₃ composite was synthesized. The composite was characterized by ¹³C cross polarization/magic angle spinning (CP/MAS) and scanning electron microscopy (SEM). The polymer ligand stabilizes the Ca–O (carboxylate) bond in the CaCO₃ composite. This prevents dissociation due to pK_a shifts of the NH·O hydrogen bond and controls the crystal growth toward metastable vaterite.     

NMR study on electronic and magnetic state in RTiO3 (R=La,Y)

The electronic and magnetic states in perovskite titanates, RTiO₃ have been investigated microscopically by NMR. In the ferromagnetically-ordered state of YTiO₃, (T_c=25K) there exist two magnetically-inequivalent Ti sites with slightly different internal fields, H_int, corresponding to the reduced Ti moments of 0.69 and 0.76 _B H_int of⁸⁹Y is –10.3 kOe in YTiO₃, while H_int at the¹³⁹La site is canceled out in the antiferromagnetic LaTiO₃. Nuclear spin-lattice relaxation time, T₁, of⁸⁹Y increase drastically with decreasing temperature below 60K where the ferromagnetic alignment of Ti moments induced by external filed seems to grow up. T₁ of¹³⁹La in Sr-doped LaTiO₃ obeys the Korringa relation, T₁T=const. of which value increases critically on approaching the Mott insulator-metal transition.The present work is supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture of Japan.     

Vision-assisted control for manipulation using virtual fixtures

We present the design and implementation of a vision-based system for cooperative manipulation at millimeter to micrometer scales. The system is based on an admittance control algorithm that implements a broad class of guidance modes called virtual fixtures. A virtual fixture, like a real fixture, limits the motion of a tool to a prescribed class or range of motions. We describe how both hard (unyielding) and soft (yielding) virtual fixtures can be implemented in this control framework. We then detail the construction of virtual fixtures for point positioning and curve following as well as extensions of these to tubes, cones, and sequences thereof. We also describe an implemented system using the JHU Steady Hand Robot. The system uses computer vision as a sensor for providing a reference trajectory, and the virtual fixture control algorithm then provides haptic feedback to implemented direct, shared manipulation. We provide extensive experimental results detailing both system performance and the effects of virtual fixtures on human speed and accuracy.