On the Maximum Skidding Output of the "Timberjack 380" Forest Tractor

An analysis has been carried out of the skidding operations performed by the "Timberjack 380" forest tractor for an initial thinning of a Pinusradiata D. Don plantation. Knowing the maximum tractive force exerted by the tractor and allowing for the different resistances to forward movement (rolling friction, slope and load resistance), it has been calculated that the tractor can skid 10.1 m3 of material on a dry, compacted earth track, and 5.2 m3 on a wet track. An examination of the various phases of the operations shows that total time per trip to be expressed by the following relation: s„ su -aV where su (speed of tractor without load) = 151.45 m/ min a = 13.4352 V = volume transported d = skidding distance. On the basis of this relation and of the more general one expressing the output (P = 60 V/T), the maximum output was calculated for the "trip without load" phase and for the whole log removal phase. For the "trip with load" phase the maximum output, whatever the skidding distance, is obtained by transporting 5.636 m3, while, for the whole cycle, to achieve the maximum output the load should be 6.970 m3 over a distance of 800 m, and 8.180 m3 over a distance of 100 m. From the analysis carried out and the results obtained, it is clear that the tractor, to ensure maximum performance, should transport material having a high unit volume, such as that obtained from clearcut-ting operations

Current status of myocardial perfusion imaging after percutaneous transluminal coronary angioplasty

AbstractControversy exists with regard to the diagnostic accuracy and optimal technique of myocardial perfusion imaging after coronary angioplasty. Exercise treadmill testing is inexpensive, with adequate predictive value for restenosis and clinical events in patients with single vessel coronary angioplasty with a normal rest electrocardiogram (ECG). Myocardial tomography has advantages for assessing patients with multivessel coronary angioplasty. Exercise stress imaging is generally preferable to pharmacologic stress in patients without physical limitations after angioplasty. Delayed thallium-201 imaging and reinjection protocols may be useful to reconcile whether residual ischemia exists in “fixed” perfusion defects. Appropriately timed stress myocardial perfusion imaging 2 to 4 weeks after procedurally successful coronary angioplasty can document improved cardiac functional capacity and reduced ECG and imaging evidence of myocardial ischemia. Although routine serial postangioplasty evaluations cannot be recommended, stess myocardial imaging may be valuable in subjects with defective anginal nocioception or extensive myocardium at risk in the area subtended by the angioplasty vessel

A numerical investigation on the use of the virtual element method for topology optimization on polygonal meshes

A classical formulation of topology optimization addresses the problem of finding the best distribution of an assigned amount of isotropic material that minimizes the work of the external forces at equilibrium. In general, the discretization of the volume-constrained minimum compliance problem resorts to the adoption of four node displacement-based finite elements, coupled with element-wise density unknowns. When regular meshes made of square elements are used, well-known numerical instabilities arise, see in particular the so-called checkerboarded patterns. On the other hand, when unstructured meshes are needed to cope with geometry of any shape, additional instabilities can steer the optimizer towards local minima instead of the expected global one. Unstructured meshes approximate the strain energy of the members of the arising optimal design with an accuracy that is strictly related to the geometrical features of the discretization, thus remarkably affecting the achieved layouts. In light of the above remarks, in this contribution we consider polygonal meshes and implement the virtual element method (VEM) to solve two classes of topology optimization problems. The robustness of the adopted discretization is exploited to address problems governed by (nearly incompressible and compressible) linear elasticity and problems governed by Stokes equations. Numerical results show the capabilities of the proposed polygonal VEM-based approach with respect to more conventional discretizations

VEM and topology optimization on polygonal meshes

Topology optimization is a fertile area of research that is mainly concerned with the automatic generation of optimal layouts to solve design problems in Engineering. The classical formulation addresses the problem of finding the best distribution of an isotropic material that minimizes the work of the external loads at equilibrium, while respecting a constraint on the assigned amount of volume. This is the so-called minimum compliance formulation that can be conveniently employed to achieve stiff truss-like layout within a two-dimensional domain. A classical implementation resorts to the adoption of four node displacement-based finite elements that are coupled with an elementwise discretization of the (unknown) density field. When regular meshes made of square elements are used, well-known numerical instabilities arise, see in particular the so-called checkerboard patterns. On the other hand, when unstructured meshes are needed to cope with geometry of any shape, additional instabilities can steer the optimizer towards local minima instead of the expected global one. Unstructured meshes approximate the strain energy of truss-like members with an accuracy that is strictly related to the geometrical features of the discretization, thus remarkably affecting the achieved layouts. In this paper we will consider several benchmarks of truss design and explore the performance of the recently proposed technique known as the Virtual Element Method (VEM) in driving the topology optimization procedure. In particular, we will show how the capability of VEM of efficiently approximating elasticity equations on very general polygonal meshes can contribute to overcome the aforementioned mesh-dependent instabilities exhibited by classical finite element based discretization technique

The 1999 Quadrantids and the lunar Na atmosphere

Enhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical-physical properties of the Leonid and Quadrantid streams may be responsible for the differenc

Peranan Metode Activity Based Costing Dalam Menentukan Cost of Goods Manufactured

The purpose of this research is to know production process of a textile company in Bandung and to analyze the comparison between cost of goods manufactured calculation methods, that applied in the company (traditional costing method) and Activity Based Costing (ABC) method. The obatained data was performed monthly during the year 2009. Based on analysis result, Cost Of Goods Manufactured calculation for unpattern material using ABC method resulted the Cost Of Goods Manufactured that is lower than traditional costing method, and Cost Of Goods Manufactured calculation for pattern material using ABC method resulted the Cost Of Goods Manufactured that is higher than traditional costing method. ABC method can describes the real consumption resource needed in production process