Acoustic black holes in a two-dimensional "photon-fluid"

Optical field fluctuations in self-defocusing media can be described in terms of sound waves in a 2D photon-fluid. It is shown that, while the background fluid couples with the usual flat metric, sound-like waves experience an effective curved spacetime determined by the physical properties of the flow. In an optical cavity configuration, the background spacetime can be suitably controlled by the driving beam allowing the formation of acoustic ergoregions and event horizons. An experiment simulating the main features of the rotating black hole geometry is proposed.Comment: revised versio

PENGGUNAAN TANAH LIAT UNTUK MENGURANGI JUMLAH SEMEN PADA BETON GEOPOLIMER

Perkembangan teknologi di bidang rekayasa struktur dan penggunaan beton semen sebagai salah satu alternatif bahan bangunan masih banyak digunakan. Hal ini karena bahan penyusun beton seperti semen, agregat, dan air mudah didapatkan. Akan tetapi, penggunaan semen banyak menimbulkan masalah, yaitu adanya gas karbondioksida (CO2) yang dilepaskan ke udara pada saat produksi semen yang dapat mengakibatkan pemanasan global. Banyaknya gas karbondioksida sebanding dengan produksi semen tersebut (Davidovits, 1994), dapat dibayangkan semakin banyak semen dikonsumsi, maka semakin banyak pula gas karbondioksida yang di produksi. Hal inilah yang merupakan salah satu faktor pendorong ditemukannya bahan alternatif berupa beton geopolimer yang menggunakan berbagai bahan mineral alam seperti fly ash, tanah liat, dan lain-lain yang berfungsi sebagai bahan baku sintesis geopolimer. Tanah liat memiliki kandungan unsur kimia yang hampir sama dengan semen yaitu mengandung Alumunium (Al), Silika (Si), Besi Oksida (FeO) dan Magnesium Oksida (MgO) yang mempunyai peran penting dalam mempercepat proses pengikatan dan pengerasan pada beton. Namun berdasarkan hasil pengujian kuat tekan yang dilakukan pada umur beton 28 hari, pengurangan jumlah semen dengan geopolimer tidak memberikan hasil kuat tekan yang lebih baik dibandingkan dengan beton konvensional, karena didalam unsur kimia tanah liat tidak terdapat unsur Kalsium (CaO) yang membentuk kekuatan beton geopolimer

Creation of helicopter dynamic systems digital twin using multibody simulations

International audienceThis paper presents a new approach to develop digital twins of helicopter dynamic systems. Helicopter industries attach growing attention to the development of digital twins to be more predictive of mechanical parts lifetime. The number of sensors available to measure loads during flights is limited. Complementary simulations are necessary to compute all the loads that the mechanical parts undergo. A new process is described to build these simulations fed with flights data records. Complexity of helicopters dynamics systems leads to create several local models of subsystems using a multibody dynamic formalism. A study focused on a swashplate rotor assembly is presented to illustrate this approach, including a new model of bearing and its validation based on bench tests

An empirical analysis of smart contracts: platforms, applications, and design patterns

Smart contracts are computer programs that can be consistently executed by a network of mutually distrusting nodes, without the arbitration of a trusted authority. Because of their resilience to tampering, smart contracts are appealing in many scenarios, especially in those which require transfers of money to respect certain agreed rules (like in financial services and in games). Over the last few years many platforms for smart contracts have been proposed, and some of them have been actually implemented and used. We study how the notion of smart contract is interpreted in some of these platforms. Focussing on the two most widespread ones, Bitcoin and Ethereum, we quantify the usage of smart contracts in relation to their application domain. We also analyse the most common programming patterns in Ethereum, where the source code of smart contracts is available.Comment: WTSC 201

Reformulation of Boundary String Field Theory in terms of Boundary State

We reformulate bosonic boundary string field theory in terms of boundary state. In our formulation, we can formally perform the integration of target space equations of motion for arbitrary field configurations without assuming decoupling of matter and ghost. Thus, we obtain the general form of the action of bosonic boundary string field theory. This formulation may help us to understand possible interactions between boundary string field theory and the closed string sector.Comment: 13 page