Unifying Dynamical and Structural Stability of Equilibriums

We exhibit a fundamental relationship between measures of dynamical and structural stability of equilibriums, arising from real dynamical systems. We show that dynamical stability, quantified via systems local response to external perturbations, coincides with the minimal internal perturbation able to destabilize the equilibrium. First, by reformulating a result of control theory, we explain that harmonic external perturbations reflect the spectral sensitivity of the Jacobian matrix at the equilibrium, with respect to constant changes of its coefficients. However, for this equivalence to hold, imaginary changes of the Jacobian's coefficients have to be allowed. The connection with dynamical stability is thus lost for real dynamical systems. We show that this issue can be avoided, thus recovering the fundamental link between dynamical and structural stability, by considering stochastic noise as external and internal perturbations. More precisely, we demonstrate that a system's local response to white-noise perturbations directly reflects the intensity of internal white noise that it can accommodate before asymptotic mean-square stability of the equilibrium is lost.Comment: 13 pages, 2 figure

Resilience, reactivity and variability : A mathematical comparison of ecological stability measures

In theoretical studies, the most commonly used measure of ecological stability is resilience: ecosystems asymptotic rate of return to equilibrium after a pulse-perturbation $-$or shock. A complementary notion of growing popularity is reactivity: the strongest initial response to shocks. On the other hand, empirical stability is often quantified as the inverse of temporal variability, directly estimated on data, and reflecting ecosystems response to persistent and erratic environmental disturbances. It is unclear whether and how this empirical measure is related to resilience and reactivity. Here, we establish a connection by introducing two variability-based stability measures belonging to the theoretical realm of resilience and reactivity. We call them intrinsic, stochastic and deterministic invariability; respectively defined as the inverse of the strongest stationary response to white-noise and to single-frequency perturbations. We prove that they predict ecosystems worst response to broad classes of disturbances, including realistic models of environmental fluctuations. We show that they are intermediate measures between resilience and reactivity and that, although defined with respect to persistent perturbations, they can be related to the whole transient regime following a shock, making them more integrative notions than reactivity and resilience. We argue that invariability measures constitute a stepping stone, and discuss the challenges ahead to further unify theoretical and empirical approaches to stability.Comment: 35 pages, 7 figures, 2 table

PEMILIHAN MINYAK PELUMAS/OLI KENDARAAN BERMOTOR

Lubricant oil is one of the important factor that must be paid attention in a machine maintenance. Majority lubricant oil choosed based on SAE parameter according to the machine specification such us 5W50, 15W50, 15W40 etc. But beside that there are something else very important to know the quality of the lubricant oil that we use it’s “Sertification Standard” such us API (American Petroleum Institute), ACEA (Association Des Constructeurs Europeen d’Automobiles), ILSAC (Erupe), JASO (Japan Automotive Standard Organization), and the other specification standards that special from producer company to legitimate lubricant, mean that the lubricant oil tested and agree on decided by the producer for used in there production vehicle

A Complexity Science - Based Management Framework for Virtual Organisations

The virtual organisation challenges traditional management assumptions because a new means of coordinating globally dispersed employees is needed. To understand the collective activities of a workforce separated by space and time, this paper describes a complexity science-based management framework for virtual organisations. Specific focus is on a South African virtual organisation as a complex adaptive system. A single, embedded case study strategy was followed, and multiple data sources used to generate theory. In this paper, results are reported that clarify the management of an organisation where technology replaces conventional face-to-face contexts for socialisation and assimilation. The paper shows how managers create a virtual context for sharing meaning and interaction through synergy, empowerment, participation and an accountable, committed workforce.virtual organisation, management, complexity science

PENGELASAN TUNGSTEN BIT PADA DRILL BIT DENGAN MENGGUNAKAN LAS ASETILIN

Berdasarkan definisi dari Dutche industrie Normen (DIN) Las adalah ikatan metalurgi pada sambungan logam atau logam paduan yang dilaksanakan dalam keadaan lumer atau cair. Dari defenisi tersebut dapat di jabarkan bahwa las adalah sambungan setempat dari beberapa batang logam dengan menggunakan energi panas. Menurut jenisnya pengelasan dibagi dua macam yaitu pengelasan listrik dan pengelasan gas. Prinsip kedua pengelasan tersebut pada dasarnya sama, yaitu dengan prinsip pencairan logam. Akan tetapi pada las gas menggunakan panas yang dihasilkan dari nyala api hasil pembakaran bahan bakar gas dengan zat asam atau oksigen sebagai energinya. Pada pengelasan drill bit menggunakan las oxy- asetylin akan lebih baik dan sempurna apabila memakai kawat las yaitu tungsten bit. Bahan yang digunakan dalam proses pengelasan tungsten bit pada drill bit dengan menggunakan las asetelin adalah: Drill bit yang akan di perbaiki, Kawat las yang digunakan Tungsten bit, Kawat las kuningan, Burax. Pengelasan tungsten bit pada drill bit dengan asetelin adalah proses perbaikan mata drill bit dengan pencairan keduanya sehingga terbentuk kembali

ANALISA KERUSAKAN LAGGING PULLEY PADA BELT CONVEYOR

Batubara merupakan salah satu potensi alam yang cukup menjanjikan di daerah Sumatera Selatan, khususnya di pertambangan batubara Tanjung Enim. Dalam proses pengangkutan material batubara digunakan belt conveyor, belt conveyor itu sendiri berfungsi sebagai suatu alat pengangkut atau memindahkan material batubara dari tempat satu ke tempat lainnya, belt conveyor sendiri memiliki kelebihan dan keunggulan, diantaranya ; kapasitas angkut yang besar, aliran bahan yang diangkutnya kontinyu, daya penggerak yang diperlukan relatif kecil dan tidak terlalu bising dalam pengoperasiannya. Pada permukaan pulley dari suatu conveyor terdapat pelapis karet yang berfungsi untuk menambah nilai koefisien gesekan antara permukaan pulley dan bagian bawah dari belt conveyor, mencegah belt slip, memperkecil beban dari counter weight, mengurangi stress pada belt serta memperpanjang usia permukaan belt

Improved numerical methods for infinite spin chains with long-range interactions

We present several improvements of the infinite matrix product state (iMPS) algorithm for finding ground states of one-dimensional quantum systems with long-range interactions. As a main new ingredient we introduce the superposed multi-optimization (SMO) method, which allows an efficient optimization of exponentially many MPS of different length at different sites all in one step. Hereby the algorithm becomes protected against position dependent effects as caused by spontaneously broken translational invariance. So far, these have been a major obstacle to convergence for the iMPS algorithm if no prior knowledge of the systems translational symmetry was accessible. Further, we investigate some more general methods to speed up calculations and improve convergence, which might be partially interesting in a much broader context, too. As a more special problem, we also look into translational invariant states close to an invariance braking phase transition and show how to avoid convergence into wrong local minima for such systems. Finally, we apply the new methods to polar bosons with long-range interactions. We calculate several detailed Devil's Staircases with the corresponding phase diagrams and investigate some supersolid properties.Comment: Main text: 17 pages plus references, 8 figures. Supplementary info: 6 pages. v2: improved presentation and more results adde