Positive Drift Research Articles

Perspective analysis outcomes of selected tribodiagnostic data used as input for condition based maintenance

The aim of this article is to estimate system soft failure occurrence and residual technical life in order to optimise firmly planned preventive maintenance. To do this, selected wear particles from oil field data are analysed. Using a large tribodiagnostic dataset we estimate the residual technical life of the observed system statistically. The dataset includes information about particles contained in oil which testify to oil conditions as well as system conditions. We focus here on the wear particles which we (and other analysts) consider to be interesting, ferrum (Fe) and lead (Pb), regarded as contact degradation and wear products. By modelling the occurrence of particles in oil we plan to determine the expected moment when soft failure occurs; this moment might then be set as the time to perform preventive maintenance (PM). Both operation time and calendar time are used here for modelling, for soft failure occurrence determination and for residual technical life estimation. The modelling is based on the specific characteristics of two diffusion processes, the Wiener process (WP) with positive drift and the Ornstein–Uhlenbeck process (OUP). We also applied a fuzzy inference system to support our first results from the diffusion processes as there is a level of uncertainty and fuzziness in the oil field data. Following the modelling outcomes we are able to judge the system hazard rate, predict expected mean residual life and set up principles of “condition based maintenance” (CBM) for this system. However, the possible uses of our outcomes are much wider. For example, they can be used as inputs for operation and mission planning, and life cycle costs can be significantly reduced thanks to the maintenance optimisation.

Optimal reinsurance with both proportional and fixed costs

This paper investigates an optimal reinsurance problem with both proportional and fixed transaction costs. Associated with a reinsurance, the proportional cost is usually charged by the reinsurer and the fixed cost occurs at the beginning of the reinsurance due to consultant commission. We describe an insurer’s original cash reserve process by a Brownian motion with positive drift. The insurer aims to minimize its ruin probability by taking a dynamic reinsurance strategy. This leads to a mixed regular control and optimal stopping problem. We solve it by establishing a connection with an optimal stopping problem. The value function and the optimal reinsurance strategy are obtained explicitly.

Centrosome nucleates numerous ephemeral microtubules and only few of them participate in the radial array.

It is generally accepted that long microtubules (MTs) grow from the centrosome with their minus ends anchored there and plus ends directed towards cell membrane. However, recent findings show this scheme to be an oversimplification. To further analyze the relationship between the centrosome and the MT array we undertook a detailed study on the MTs growing from the centrosome after microinjection of Cy3 labeled tubulin and transfection of cells with EB1-GFP. To evaluate MTs around the centrosome two approaches were used: path photobleaching across the centrosome area (Komarova et al., ) and sequential image subtraction analysis (Vorobjev et al., ). We show that about 50% of MTs had been nucleated at the centrosome are short-living: their mean length was 1.8 ± 0.8 μm and their life span - 7 ± 2 s. MTs initiated from the centrosome also rarely reach cell margin, since their elongation was limited and growth after shortening (rescue) was rare. After initial growth all MTs associated with the centrosome converted to pause or shortening. After pause MTs associated with the centrosome mainly depolymerized via the plus end shortening. Stability of the minus ends of cytoplasmic MTs was the same as for centrosomal ones. We conclude that in fibroblasts (1) the default behavior of free MTs in the cell interior is biased dynamic instability (i.e., random walk of the plus ends with significant positive drift); (2) MTs born at the centrosome show "dynamic instability" type behavior with no boundary; and (3) that the extended radial array is formed predominantly by MTs not associated with the centrosome.

A quickest detection problem with an observation cost

In the classical quickest detection problem, one must detect as quickly as possible when a Brownian motion without drift “changes” into a Brownian motion with positive drift. The change occurs at an unknown “disorder” time with exponential distribution. There is a penalty for declaring too early that the change has occurred, and a cost for late detection proportional to the time between occurrence of the change and the time when the change is declared. Here, we consider the case where there is also a cost for observing the process. This stochastic control problem can be formulated using either the notion of strong solution or of weak solution of the s.d.e. that defines the observation process. We show that the value function is the same in both cases, even though no optimal strategy exists in the strong formulation. We determine the optimal strategy in the weak formulation and show, using a form of the “principle of smooth fit” and under natural hypotheses on the parameters of the problem, that the optimal strategy takes the form of a two-threshold policy: observe only when the posterior probability that the change has already occurred, given the observations, is larger than a threshold $A\geq0$, and declare that the disorder time has occurred when this posterior probability exceeds a threshold $B\geq A$. The constants $A$ and $B$ are determined explicitly from the parameters of the problem.

Model Uncertainty in Commodity Markets

Agents who acknowledge that their models are incorrectly specified are said to be ambiguity averse, and this affects the prices they are willing to trade at. Models for prices of commodities attempt to capture three stylized features: seasonal trend, moderate deviations (a diffusive factor), and large deviations (a jump factor) both of which mean-revert to the seasonal trend. Here we model ambiguity by allowing the agent to consider a class of models absolutely continuous w.r.t. their reference model, but penalize candidate models that are far from it. We show that the buyer (seller) of a forward contract introduces a negative (positive) drift in the dynamics of the spot price, and enhances downward (upward) jumps so the prices they are willing to trade at are lower (higher) than that of the forward price under P. When ambiguity averse buyers and sellers employ the same reference measure they cannot trade because the seller requires more than what the buyer is willing to pay. Finally, we observe that when ambiguity averse agents price options written on the commodity forward, the effect of ambiguity aversion is strongest when the option is at-the-money, and weaker when it is deep in-the-money or deep out-of-the-money.

Energy intensive infrastructure investments with retrofits in continuous time: Effects of uncertainty on energy use and carbon emissions

Energy-intensive infrastructure may tie up fossil energy use and carbon emissions for a long time after investment, and thus be crucial for the ability to control long-run emissions. Much or most of the resulting carbon emissions can often be eliminated later, through a retrofit that may however be costly. This paper studies the joint decision to invest in such infrastructure, and retrofit it later, given that future climate damages are uncertain and follow a geometric Brownian motion process with positive drift. We find that higher climate cost volatility (for given unconditional expected costs) then delays the retrofit decision by increasing the option value of waiting to invest. The initial infrastructure is also chosen with higher energy intensity, further increasing total emissions, when volatility is higher. We provide conditions under which higher climate cost volatility increases total expected discounted climate damage from the infrastructure, which happens in a wide set of circumstances.

System Condition Estimation Based on Selected Tribodiagnostic Data

The aim of the paper is to estimate a system-soft failure occurrence and residual technical life. When estimating a residual technical life statistically, usually a big amount of tribodiagnostic data is used. Data include the information about particles contained in oil that testifies to oil and system conditions. We focus here on the particles that we consider to be interesting. They are ferrum (Fe) and lead (Pb) as contact degradation product. By modelling the occurrence of particles in oil, we expect to determine the expected moment for soft failure occurrence or adequate moment to perform preventive maintenance. The way of our modelling is based on the specific characteristics of diffusion processes, namely the Wiener process with positive drift and Ornstein–Uhlenbeck process. Following the modelling results, we could judge hazard rate and set-up principles of ‘CBM - Condition Based Maintenance’ (CBM). However, the possibilities are much wider, because we can also plan operation, mission and reduce life cost. Copyright © 2015 John Wiley & Sons, Ltd.

Optimal Dividend Policy when Cash Reserves Follow a Jump-Diffusion Process Under Markov-Regime Switching

In this paper we study the optimal dividend payments for a company of limited liability whose cash reserves in the absence of dividends follow a Markov-modulated jump-diffusion process with positive drifts and negative exponential jumps, where parameters and discount rates are modulated by a finite-state irreducible Markov chain. The main aim is to maximize the expected cumulative discounted dividend payments until bankruptcy time when cash reserves are nonpositive for the first time. We extend the results of Jiang and Pistorius [15] to our setup by proving that it is optimal to adopt a modulated barrier strategy at certain positive regime-dependent levels and that the value function can be explicitly characterized as the fixed point of a contraction.

Optimal Dividend Policy when Cash Reserves Follow a Jump-Diffusion Process Under Markov-Regime Switching

In this paper we study the optimal dividend payments for a company of limited liability whose cash reserves in the absence of dividends follow a Markov-modulated jump-diffusion process with positive drifts and negative exponential jumps, where parameters and discount rates are modulated by a finite-state irreducible Markov chain. The main aim is to maximize the expected cumulative discounted dividend payments until bankruptcy time when cash reserves are nonpositive for the first time. We extend the results of Jiang and Pistorius [15] to our setup by proving that it is optimal to adopt a modulated barrier strategy at certain positive regime-dependent levels and that the value function can be explicitly characterized as the fixed point of a contraction.

Buffer-overflows: Joint limit laws of undershoots and overshoots of reflected processes

Let τ(x) be the epoch of first entry into the interval (x,∞), x>0, of the reflected process Y of a Lévy process X, and define the overshoot Z(x)=Y(τ(x))−x and undershoot z(x)=x−Y(τ(x)−) of Y at the first-passage time over the level x. In this paper we establish, separately under the Cramér and positive drift assumptions, the existence of the weak limit of (z(x),Z(x)) as x tends to infinity and provide explicit formulas for their joint CDFs in terms of the Lévy measure of X and the renewal measure of the dual of X. Furthermore we identify explicit stochastic representations for the limit laws. We apply our results to analyse the behaviour of the classical M/G/1 queueing system at buffer-overflow, both in a stable and unstable case.

Superelastic load cycling of Gum Metal

The superelastic beta titanium alloy, Gum Metal, has been found to accumulate plastic strain during tensile load cycling in the superelastic regime. This is evident from the positive drift of the macroscopic stress vs. strain hysteresis curve parallel to the strain axis and the change in its geometry subsequent to every load–unload cycle. In addition, there is a progressive reduction in the hysteresis loop width and in the stress at which the superelastic transition occurs. In situ synchrotron X-ray diffraction has shown that the lattice strain exhibited the same behaviour as that observed in macroscopic measurements and identified further evidence of plastic strain accumulation. The mechanisms responsible for the observed behaviour have been evaluated using transmission electron microscopy, which revealed a range of different defects that formed during load cycling. The formation of these defects is consistent with the classical mathematical theory for the bcc to orthorhombic martensitic transformation. It is the accumulation of these defects over time that alters its superelastic behaviour.

The post-repurchase announcement drift: an anomaly in disguise?

Purpose – The purpose of this paper is to reexamine the stock price drifts after open-market stock repurchase announcements by differentiating actual repurchases from repurchase announcements and by controlling for the repurchasing firms’ earnings improvement in the announcement year relative to the prior year. Design/methodology/approach – The authors use the calendar-time method and matching method based on different criteria to calculate the post-announcement abnormal returns. Findings – The results show that only firms actually repurchasing their shares exhibit a positive post-announcement drift. More importantly, the authors find that these repurchasing firms have the same post-announcement drift as their matching firms that have similar size and earnings performance but do not repurchase. This supports the argument that the post-repurchase announcement drift found in previous studies is not a distinct anomaly but the post-earnings announcement drift in disguise. Social implications – The post-repurchase announcement drift found in previous studies is the post-earnings announcement drift in disguise. Originality/value – The study shows that because high earnings performance positively relates to real repurchase activities, controlling for earnings performance in examining whether a drift occurs after repurchase announcements.

Exponential energy growth in adiabatically changing Hamiltonian systems.

We show that the mixed phase space dynamics of a typical smooth Hamiltonian system universally leads to a sustained exponential growth of energy at a slow periodic variation of parameters. We build a model for this process in terms of geometric Brownian motion with a positive drift, and relate it to the steady entropy increase after each period of the parameters variation.

Fast Fermi Acceleration and Entropy Growth

Fermi acceleration is the process of energy transfer from massive objects in slow motion to light objects that move fast. The model for such process is a time-dependent Hamiltonian system. As the parameters of the system change with time, the energy is no longer conserved, which makes the acceleration possible. One of the main problems is how to generate a sustained and robust energy growth. We show that the non-ergodicity of any chaotic Hamiltonian system must universally lead to the exponential growth of energy at a slow periodic variation of parameters. We build a model for this process in terms of a Geometric Brownian Motion with a positive drift and relate it to the entropy increase.

Four Years of Daily Photon Emissions That Have Predicted Major Earthquakes: Raw Data, Spectral Power Density Analyses and Implications for the Geosciences

The daily median ground surface flux densities per day from a continuously operating photomultiplier tube unit for four years in Sudbury, Ontario are presented for December 2010 to December 2014. Increases of about 2 to 4 PMT units (1 unit = 5 × 10-11 W·m-2) for median daily measures reliably occurred about two weeks before M ≥ 7.7 earthquakes anywhere on the planet. The PMT units, until June 2014, usually returned to baseline within a few days after the events. There has been a slow positive drift in flux power density since about 2012 and a conspicuous maintained increase after May, 2014. The equivalent energy per day if it were represented isotropically within the volume occupied by the earth is the same order of magnitude as the average daily global total seismic energy release. Spectral power densities revealed enhanced peaks (periodicities) between 100 to 150 days, 60 days, 30 days, and 25 days. Discriminable peaks in power were noted around 18 days, 14 days, and 4 to 6 days. These results suggest that continuous measurement of photonemissions within hyper-dark conditions may reveal geophysical processes that precede larger seismic events and could reflect the movement of the earth-solar system around the galactic center.

Changing Laws in Rape - A positive Drift to Accomplishment in the Legal System of India

As we are advancing towards the 21st century, we the Indians having accomplished greater pinnacles in the area of technology, aerospace research, academics and also in the field of economics; there is an immense need for the legal system to change and move ahead in a positive direction. The archive acts still prevailing from the British rule even though they have left us, long back! Law needs to be more sympathetic and sensitive towards the victims of this heinous atrocious crime in so that they barely need be reminded of it. Most often the victim is abused and humiliated and that is the regular sight in the present legal scenario.

English

Two group of 50 patients each of DES were taken for study with schirmer's test - 1 value of <7 mm/ 5min .Group A received artificial tear & nutritional supplements of EFAs for 8 weeks and Group B received artificial tears only for 8 week . Study reveals that dietary intervention with omega- 3 fatty acid not only causes symptomatic improvement but also betters clinical markers of dry eye as seen by a positive drift in primary and secondary outcome measures. There is a likely improvement in inherent stability of the tear film as seen by the larger TBUT drift and CIC scores. This paper will discuss the results in detail. INTRODUCTION: Dry eye syndrome (DES) is a multifactorial disease, affecting tears and the ocular surface. It is accompanied by increased osmolarity of tear film, and inflammation of the ocular surface.(1)-(3) Despite recent advances in understanding the etiopathogenesis of DES, there remain a lacuna in diagnosis, prevention and definitive treatment. DES is a common problem worldwide and can reduce the working efficiency of an individual. Dry eye is therefore a frequent reason that patient present to eye care clinics. Common patient's complaints related to dry eye include reduced vision, difficulty reading, difficulty driving at night and difficulty doing computer work.(5) Most diagnostic tests for dry eye are poorly standardized, making compare between studies tenuous at best. A generally agreed upon 'gold standard' still does not exist. Additionally, some of these tests are poorly associated with subjective symptoms. (6)-(7)

Dividend Initiations, Increases and Idiosyncratic Volatility

We examine three aspects of the relation between dividend initiation and increase announcements and idiosyncratic volatility. First, consistent with dividend signaling, we find that firms with higher levels of idiosyncratic volatility are associated with higher announcement abnormal returns when initiating or increasing dividends. Second, high idiosyncratic volatility firms are associated with stronger positive post event return drift. Finally, firms on average experience an ex post reduction in idiosyncratic volatility following dividend initiations that is associated with announcement and long-term abnormal returns.

Molecular communication with Brownian motion and a positive drift: performance analysis of amplitude modulation schemes

In this study, the authors consider molecular communication between two nanomachines placed in a fluid medium for three different amplitude modulation schemes. The number of molecules transmitted represents the amplitude levels for these schemes. Each molecule released by the transmitter travels with Brownian motion and a positive drift to reach the receiver nanomachine. They consider a time slotted channel, where the information in every slot is corrupted by stray molecules from the previous slots. The capacity of such a molecular communication channel is investigated for all the three modulation schemes. Analytical expressions for the end-to-end symbol error probability are derived, considering maximum likelihood detection at the receiver. Numerical results indicate that arbitrarily low probabilities of error can be achieved for high drift velocities. An increase in the slot length further improves the performance, albeit at the cost of data rate. The results also demonstrate the improvements offered by the amplitude modulation schemes over the previously proposed time modulation schemes.

Decameter Type III Bursts with Changing Frequency Drift-Rate Signs

We discuss properties of type III bursts which change sign of their drift rate from negative to positive and vice versa. Moreover such bursts may change sign of their drift rates more than once. These specific type III bursts were observed simultaneously by radio telescopes UTR-2, URAN-2 and NDA in frequency band 8-41 MHz. The negative drift rates of these bursts are close to those of usual decameter type III bursts and variate from -0.84 MHz/s to -5.56 MHz/s. The positive drift rates of specific type III bursts vary in the wider range from 0.44MHz/s to 12 MHz/s. Unlike inverted U-bursts these type III bursts still drift from the high frequencies to the low frequencies in spite of the change of the drift rates signs. Our basic explanation of the positive drift rate of these type III burst differs from the common assumption that positive drift rates of Type III bursts are connected with electron beam propagation towards the Sun. We propose that, even if electron beams move outward from the Sun, they can generate type III bursts with positive drift rates if in some regions of the solar corona the group velocities of type III radio emissions are lower than the velocities of the electron beams.