Theoretical and experimental studies of the dynamics and acoustics of forced ordered granular networks

Ordered arrays of granular particles (beads) have attracted considerable attention in recent years due to their rich dynamical behaviors and interesting properties. Depending on the ratio of static to dynamic deformations between particles the dynamics of granular media is highly tunable ranging from being strongly nonlinear and non-smooth in the absence of static pre-compression, to reducing to weakly nonlinear and smooth for large static pre-compression. The nonlinearity in uncompressed granular media arises from two sources: First, nonlinear Hertzian interactions, which can be modeled mathematically, between beads in contact, and second, bead separations in the absence of compressive forces between them leading to collisions between adjacent beads. When no applied pre-compression exists there is complete absence of linear acoustics in ordered granular media, which results in zero speed of sound as defined in the sense of linear acoustics through the classical wave equation; thus, these media have been characterized as “sonic vacua”. However, various nonlinear waves can still propagate in these media with energy tunable properties. The first part of this dissertation aims to study the frequency responses of a single homogenous granular chain. We consider a one-dimensional uncompressed granular chain composed of a finite number of identical spherical elastic beads with Hertzian interactions. The chain is harmonically excited by an amplitude- and frequency-dependent boundary drive at its left end and has a fixed boundary at its right end. We computationally and experimentally detect time-periodic, strongly nonlinear resonances whereby the particles (beads) of the granular chain respond at integer multiples of the excitation period, and which correspond to local peaks of the maximum transmitted force at the chain’s right, fixed end. In between these resonances we detect local minima of the maximum transmitted forces corresponding to anti-resonances, where chimera states (i.e., coexistence of different stationary and nonstationary waveforms) are noted, in the steady-state dynamics. Furthermore, we construct a mathematical model which can completely capture the rich and complex dynamics of the system. The second part of the study is primarily concerned with the propagatory dynamics of geometrically coupled ordered granular media. In particular, we focus on primary pulse transmission in a two-dimensional granular network composed of two ordered chains that are nonlinearly coupled through Hertzian interactions. Impulsive excitation is applied to one of the chains (denoted as “excited chain”), and the resulting transmitted primary pulses in both chains are considered, especially in the non-directly excited chain (denoted as “absorbing chain”). A new type of mixed nonlinear solitary pulses – shear waves is predicted for this system, leading to primary pulse equi-partition between chains, indicating strong energy exchange between two chains through the geometric coupling. Then, an analytical reduced model for primary pulse transmission is derived to study the strongly nonlinear acoustics in the small-amplitude approximation. In contrast to the full equations of motion the simplified model is re-scalable with energy and parameter-free, and is asymptotically solved by extending the one-dimensional nonlinear mapping technique. The nonlinear maps, which are derived for this two-dimensional system and governing the amplitudes of the mixed-type waves, accurately capture the primary pulse propagation in this system and predict the first occurrence of energy or pulse equi-partition in the network. Moreover, to confirm the theoretical results we experimentally test a series of two-dimensional granular networks, and prove the occurrence of strong energy exchanges leading to eventual pulse equi-partition between the excited and absorbing chains, provided that the number of beads is sufficiently large. Then we analyze the dynamics of a granular network composed of two semi-infinite, ordered homogeneous granular chains mounted on linear elastic foundations and coupled by weak linear stiffnesses under periodic excitation. We first review the acoustic filtering properties of linear and nonlinear semi-infinite periodic media containing two attenuation zones (AZs) and one propagation zone (PZ) in the frequency domain. In both linear and nonlinear systems, under suddenly applied, high-frequency harmonic excitations, “dynamic overshoot” phenomena are realized whereby coherent traveling responses are propagating to the far fields of these media despite the fact that the high frequencies of the suddenly applied excitations lie well within the stop bands of these systems. For the case of the linear system we show that the transient dynamic overshoot can be approximately expressed in terms of the Green’s function at its free end. A different type of propagating wave in the form of a “pure” traveling breather, i.e., of a single propagating oscillatory wavepacket with a localized envelope, is realized in the transient responses of a nonlinear granular network. The pure breather is asymptotically studied by a complexification/averaging technique, showing nearly complete but reversible energy exchanges between the excited and absorbing chains as the breather propagates to the far field. We analytically prove that the reason for this dynamic overshoot phenomenon in both linear and nonlinear networks is the high rate of application of the high-frequency harmonic excitation, which, in essence, amounts approximately to an impulsive excitation of the periodic medium. Verification of the analytical approximations with direct numerical simulations is performed. We further study passive pulse redirection and nonlinear targeted energy transfer in the aforementioned weakly coupled granular network. Periodic excitation in the form of repetitive half-sine pulses is applied to the excited chain. The frequency of excitation is within the pass band of the granular system. At the steady state nearly complete but reversible energy exchanges between the two chains are noted. We show that passive pulse redirection and targeted energy transfer from the excited to the absorbing chain can be achieved by macro-scale realization of the spatial analog of the Landau-Zener quantum tunneling effect. This is realized by finite stratification of the elastic foundation of the excited chain, and depends on the system parameters (e.g., the percentage of stratification) and on the parameters of the periodic excitation. We detect the existence of two distinct nonlinear phenomena in the periodically forced network; namely, (i) energy localization in the absorbing chain due to sustained 1:1 resonance capture leading to irreversible pulse redirection from the excited chain, and (ii) continuous energy exchanges in the form of nonlinear beats between the two chains in the absence of resonance capture. Our results demonstrate that steady state passive pulse redirection in these networks can be robustly achieved under periodic excitation. The final part of present work is concerned with propagating breathers in granular networks under impulsive excitation. We apply a complexification-averaging methodology leading to smooth slow flow reduced models of the dynamics to reveal the nature of 1:1 resonance at fundamental steady-state responses of the system. The primary aim of this analytical study is to provide a predictive way to excite the system at its resonance conditions. In addition to the fundamental resonance we numerically verify the occurrences of subharmonic steady-state responses in such granular networks. We experimentally detect the propagating breathers in a single chain mounted on elastic foundations. Our experimental measurements show good correspondence with the computational results which validate our previous theoretical predications. The results of this work contribute to the design of practical nonlinear acoustic metamaterials and provide a new avenue for understanding ofthe complex nonlinear dynamics of granular media

Internationalization of the forest industry : A corporate-level analysis

With far-reaching impacts of economic globalization, the internationalization process of the forest industry has been accelerated. Particularly since the 1990s, internationalization has progressed intensively through industry consolidation and production relocation. Within the wood and wood products sector, for example, world inward foreign direct investment (FDI) stocks increased from 20 billion US dollars in 1990 to more than 120 billion US dollars in 2011. Forest industry firms have geographically shifted their operations from traditional production bases in developed countries to emerging Asian and Latin American countries. The share of FDI flows into developing and transition economies has grown from 18.8% in 1990 - 1992 to 73% in 2009 - 2011. The internationalization process of the forest industry has induced multifaceted concerns from economic, strategic, and environmental perspectives at both country and corporate level. However, the actual consequences of such expansion are still largely unknown. It is therefore important to study the current status of the forest industry s internationalization process and to explore drivers and goals of this process. The theoretical background of this thesis is mainly based on the internationalization and FDI theories portrayed in international business literature. A systematic literature review, a qualitative case study and cross-sectional regression analysis have been applied methodologically. China is used as an example in two of the empirical studies, as it is the most attractive FDI destination in the global forest sector. This thesis conceptually depicts a framework of the systematic internationalization process of the forest industry. Empirically, three themes are identified as focal topics; namely corporate financial performance, corporate sustainability, and corporate entry mode choice. Managerial implications derived from this thesis indicate that (1) firms could aim for either internationalized or domestic-oriented operational strategies to pursue higher financial performance; (2) firms should implement social and environmental assessment to maintain sustainable overseas operations; and (3) firms ought to accumulate operational experience and familiarity with local culture before investing in a wholly owned subsidiary. In general, this thesis concludes that internationalization is a dynamic process of pursuing sustainable development to tackle physical forest resource constraints, socio-economic challenges, and corporate operational risks at the global operations scale. Topics related to the analysis of new innovative products, collaboration with supporting industries, and the consideration of sustainability as corporate core competitive advantages are worthy of future research aiming to analyze the further internationalization process of the forest industry.Metsäteollisuuden kansainvälistyminen on kiihtynyt talouden globalisaation edetessä erityisesti 1990-luvun alun jälkeen. Metsäyritysten tuotantokapasiteetti on myös siirtynyt kehittyville markkinoille Latinalaiseen Amerikkaan ja Aasiaan. Kansainvälistymisprosessi on tuonut mukanaan sekä strategisia ja taloudellisia että ympäristövastuuseen liittyviä haasteita sekä yritystasolla että markkinatasolla. Metsäteollisuuden kansainvälistymiskehityksen vaikutuksia markkinoihin ja yrityksiin tunnetaan kuitenkin heikosti. Tämä tutkimus kohdistuu sen vuoksi erityisesti analysoimaan sekä metsäyritysten kansainvälistymisprosessia että sen taustalla olevia ajureita ja strategisia päämääriä. Tutkimuksen teoreettinen viitekehys perustuu yleisiin kansainvälistymisteorioihin. Metodologisesti työssä hyödynnetään systemaattista kirjallisuuskatsausta, kvalitatiivista case -tutkimusta ja poikkileikkausaineistojen regressioanalyysia. Kiina on valittu tärkeimmäksi empiirisen analyysin kohdealueeksi, koska maahan suuntautuneet metsäteollisuusinvestoinnit ovat olleet 1990-luvulta lähtien voimakkaassa kasvussa. Käsitteellisesti väitöskirja kehittää ensimmäisessä osatutkimuksessa analyysikehikon, jota myöhemmin sovelletaan työn muissa osissa. Empiirisissä osatutkimuksissa on kolme teemaa, joissa tutkitaan vaikutuksia yritysten kannattavuuteen, vaikutuksia yritysvastuuseen kehittyvillä markkinoilla ja vaikutuksia investointimuodon (engl. foreign entry mode) valintaan. Tutkimuksen tulokset viittaavat siihen että kannattavuutta tavoitellessaan yritykset voivat tähdätä joko korkeaan kansainvälistymisen asteeseen tai keskittyä kotimarkkinoihinsa. Toiseksi, yritysten vastuu sidosryhmiinsä kehittyvillä markkinoilla on laajentumassa. Kolmanneksi, investointimuotoa harkitessaan metsäyritykset ottavat huomioon kulttuuriset eronsa kohdemaan ja kotimaan välillä. Väitöskirjatutkimuksen mukaan metsäteollisuusyritysten kansainvälistyminen on dynaaminen prosessi, johon vaikuttavat mm. odotukset toimintaan liittyvistä taloudellisista ja sosiaalisista riskeistä, rajoitteet luonnovarojen hyödynnettävyydessä sekä sidosryhmien odotukset liiketoiminnan vastuullisuudesta. Jatkotutkimuksissa tulisi kiinnittää erityistä huomiota innovaatioihin ja tuotekehitykseen kansainvälistyvässä metsäteollisuudessa, sektorirajat ylittävän yhteistoiminnan mahdollisuuksiin sekä yritystoiminnan vastuullisuuden kasvavaan merkitykseen osana metsäteollisuuden kilpailukykyä globaaleilla markkinoilla

Impact of methoxyacetic acid on mouse Leydig cell gene expression

<p>Abstract</p> <p>Background</p> <p>Methoxyacetic acid (MAA) is the active metabolite of the widely used industrial chemical ethylene glycol monomethyl ether, which is associated with various developmental and reproductive toxicities, including neural toxicity, blood and immune disorders, limb degeneration and testicular toxicity. Testicular toxicity is caused by degeneration of germ cells in association with changes in gene expression in both germ cells and Sertoli cells of the testis. This study investigates the impact of MAA on gene expression in testicular Leydig cells, which play a critical role in germ cell survival and male reproductive function.</p> <p>Methods</p> <p>Cultured mouse TM3 Leydig cells were treated with MAA for 3, 8, and 24 h and changes in gene expression were monitored by genome-wide transcriptional profiling.</p> <p>Results</p> <p>A total of 3,912 MAA-responsive genes were identified. Ingenuity Pathway analysis identified reproductive system disease, inflammatory disease and connective tissue disorder as the top biological functions affected by MAA. The MAA-responsive genes were classified into 1,366 early responders, 1,387 mid-responders, and 1,138 late responders, based on the time required for MAA to elicit a response. Analysis of enriched functional clusters for each subgroup identified 106 MAA early response genes involved in transcription regulation, including 32 genes associated with developmental processes. 60 DNA-binding proteins responded to MAA rapidly but transiently, and may contribute to the downstream effects of MAA seen for many mid and late response genes. Genes within the phosphatidylinositol/phospholipase C/calcium signaling pathway, whose activity is required for potentiation of nuclear receptor signaling by MAA, were also enriched in the set of early MAA response genes. In contrast, many of the genes responding to MAA at later time points encode membrane proteins that contribute to cell adhesion and membrane signaling.</p> <p>Conclusions</p> <p>These findings on the progressive changes in gene expression induced by MAA in a cultured Leydig cell model may help elucidate signaling pathways that lead to the testicular pathophysiological responses induced by MAA exposure and may identify useful biomarkers of MAA toxicity.</p

Audio steganography with AES for real-time covert Voice over Internet Protocol communications

As a popular real-time service on the Internet, Voice over Internet Protocol (VoIP) communication attracts more and more attention from the researchers in the information security field. In this study, we proposed a VoIP steganographic algorithm with variable embedding capacities, incorporating AES and key distribution, to realize a real-time covert VoIP communication. The covert communication system was implemented by embedding a secret message encrypted with symmetric cryptography AES-128 into audio signals encoded by PCM codec. At the beginning of each VoIP call, a symmetric session key (SK) was assigned to the receiver with a Session Initiation Protocol-based authentication method. The secret message was encrypted and then embedded into audio packets with different embedding algorithms before sending them, so as to meet the real-time requirements of VoIP communications. For each audio packet, the embedding capacity was calculated according to the specific embedding algorithm used. The encryption and embedding processes were almost synchronized. The time cost of encryption was so short that it could be ignored. As a result of AES-based steganography, observers could not detect the hidden message using simple statistical analysis. At the receiving end, the corresponding algorithm along with the SK was employed to retrieve the original secret message from the audio signals. Performance evaluation with state-of-the-art network equipment and security tests conducted using the Mann-Whitney-Wilcoxon method indicated that the proposed steganographic algorithm is secure, effective, and robust

Complex modulation of androgen responsive gene expression by methoxyacetic acid

<p>Abstract</p> <p>Background</p> <p>Optimal androgen signaling is critical for testicular development and spermatogenesis. Methoxyacetic acid (MAA), the primary active metabolite of the industrial chemical ethylene glycol monomethyl ether, disrupts spermatogenesis and causes testicular atrophy. Transcriptional <it>trans</it>-activation studies have indicated that MAA can enhance androgen receptor activity, however, whether MAA actually impacts the expression of androgen-responsive genes <it>in vivo</it>, and which genes might be affected is not known.</p> <p>Methods</p> <p>A mouse TM3 Leydig cell line that stably expresses androgen receptor (TM3-AR) was prepared and analyzed by transcriptional profiling to identify target gene interactions between MAA and testosterone on a global scale.</p> <p>Results</p> <p>MAA is shown to have widespread effects on androgen-responsive genes, affecting processes ranging from apoptosis to ion transport, cell adhesion, phosphorylation and transcription, with MAA able to enhance, as well as antagonize, androgenic responses. Moreover, testosterone is shown to exert both positive and negative effects on MAA gene responses. Motif analysis indicated that binding sites for FOX, HOX, LEF/TCF, STAT5 and MEF2 family transcription factors are among the most highly enriched in genes regulated by testosterone and MAA. Notably, 65 FOXO targets were repressed by testosterone or showed repression enhanced by MAA with testosterone; these include 16 genes associated with developmental processes, six of which are <it>Hox </it>genes.</p> <p>Conclusions</p> <p>These findings highlight the complex interactions between testosterone and MAA, and provide insight into the effects of MAA exposure on androgen-dependent processes in a Leydig cell model.</p

Robust output regulation of linear system subject to modeled and unmodeled uncertainty

In this paper, a novel robust output regulation control framework is proposed for the system subject to noise, modeled disturbance and unmodeled disturbance to seek tracking performance and robustness simultaneously. The output regulation scheme is utilized in the framework to track the reference in the presence of modeled disturbance, and the effect of unmodeled disturbance is reduced by an $\mathcal{H}_\infty$ compensator. The Kalman filter can be also introduced in the stabilization loop to deal with the white noise. Furthermore, the tracking error in the presence/absence of noise and disturbance is estimated. The effectiveness and performance of our proposed control framework is verified in the numerical example by applying in the Furuta Inverted Pendulum system

Covert voice over internet protocol communications with packet loss based on fractal interpolation

The last few years have witnessed an explosive growth in the research of information hiding in multimedia objects, but few studies have taken into account packet loss in multimedia networks. As one of the most popular real-time services in the Internet, Voice over Internet Protocol (VoIP) contributes to a large part of network traffic for its advantages of real time, high flow, and low cost. So packet loss is inevitable in multimedia networks and affects the performance of VoIP communications. In this study, a fractal-based VoIP steganographic approach was proposed to realise covert VoIP communications in the presence of packet loss. In the proposed scheme, secret data to be hidden were divided into blocks after being encrypted with the block cipher, and each block of the secret data was then embedded into VoIP streaming packets. The VoIP packets went through a packet loss system based on Gilbert model which simulates a real network situation. And a prediction model based on fractal interpolation was built to decide whether a VoIP packet was suitable for data hiding. The experimental results indicated that the speech quality degradation increased with the escalating packet-loss level. The average variance of speech quality metrics (PESQ score) between the "no-embedding" speech samples and the “with-embedding” stego-speech samples was about 0.717, and the variances narrowed with the increasing packet-loss level. Both the average PESQ scores and the SNR values of stego-speech samples and the data retrieving rates had almost the same varying trends when the packet-loss level increased, indicating that the success rate of the fractal prediction model played an important role in the performance of covert VoIP communications