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Search Results: 1 - 10 of 402 matches for " Kazumi Ohkubo "
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A Case of Pleomorphic Adenoma of the Parotid Gland with Multiple Local Recurrences through Facial to Cervical Regions  [PDF]
Masanobu Abe, Yoshiyuki Mori, Yuki Kanno, Kazuto Hoshi, Hideto Saijo, Takahiro Abe, Kazumi Ohkubo, Tsuyoshi Takato
Open Journal of Stomatology (OJST) , 2014, DOI: 10.4236/ojst.2014.49059
Abstract: Pleomorphic adenoma is the most common benign parotid gland tumor. Although its local recurrence rate is known to be high, the recurrence extending to the cervical region is rare. Here we report a case of a young female (25 years old) with pleomorphic adenoma of the parotid gland which showed multiple recurrences through facial to cervical regions over a span of eight years. We also discuss how this benign tumor with a high recurrence rate has been treated in other cases, and how it should be treated.
A recruitment forecasting model for the Pacific stock of the Japanese sardine (Sardinops melanostictus) that does not assume density-dependent effects  [PDF]
Kazumi Sakuramoto
Agricultural Sciences (AS) , 2013, DOI: 10.4236/as.2013.46A001

This study developed a recruitment forecasting model based on a new concept of the stock recruitment relationship. No density-dependent effect in the relationship was assumed in the model, which showed that fluctuations in recruitment and spawning stock biomass of Japanese sardine in the northwestern Pacific can be explained mainly by environmental factors and the effects of fishing. The February Arctic Oscillation (AO) and sea surface temperature over the southern area of the Kuroshio Extension (30 - 35°N and 145 - 180°E; KEST) were used as the environmental factors. The recruitment forecasting model is proposed:


The values for recruitment (\"\"), spawning stock biomass, (\"\"), in year t, forecast by this model accurately reproduced those estimated by tuning virtual population analysis (VPA), and the pattern of variability in the stock recruitment relationship was also reproduced well. In conclusion, a

Illusion of a Density-Dependent Effect in Biology  [PDF]
Kazumi Sakuramoto
Agricultural Sciences (AS) , 2015, DOI: 10.4236/as.2015.65047
Abstract: Population changes are believed to be controlled by multiple factors, including an important density-dependent effect. This paper reviews the literature on this topic and shows that this density-dependent effect does not exist. This paper also gives a typical example in which no density-dependent effect was detected in the stock-recruitment relationship in Japanese sardines. The recruitment was found to be determined in proportion to the spawning stock biomass and to be affected by environmental factors. This simple mechanism is applicable not only in fish species but also in insects such as Thrips imaginis in Australia. The reason that many biologists have not become aware that the density-dependent effect does not exist is discussed using a metaphor. This paper proposes a new concept in the study of population change. The new concept proposed here will replace the currently used basic concept that has been assumed to be correct for more than 50 years.
A Stock-Recruitment Relationship Applicable to Pacific Bluefin Tuna and the Pacific Stock of Japanese Sardine  [PDF]
Kazumi Sakuramoto
American Journal of Climate Change (AJCC) , 2015, DOI: 10.4236/ajcc.2015.45036
Abstract: This study shows that the stock-recruitment relationship (SRR) for Pacific bluefin tuna and the Pacific stock of Japanese sardine can be expressed by the same SRR model. That is, \"\"(environmental factors), where Rt and St-1 denote the recruitment in year t and spawning stock biomass in year t - 1, and f(.) is a function that evaluates the effect of environmental factors in year t. The simulations showed that when the fluctuation in environmental factors cyclically changed, 1) the shape of the apparent SRR assumed clockwise loops for the shorter maturity age of fish, and 2) the apparent SRR comprised scattered anticlockwise loops for the longer maturity age of fish. These features coincided well with those observed. This finding gives us a new paradigm in SRR, which is far different from the concept that has predominated in the field for more than 60 years.
Case Study: A Simulation Model of the Spawning Stock Biomass of Pacific Bluefin Tuna and Evaluation of Fisheries Regulations  [PDF]
Kazumi Sakuramoto
American Journal of Climate Change (AJCC) , 2016, DOI: 10.4236/ajcc.2016.52021
Abstract: This study proposes a simulation model that well reproduces the spawning stock biomass of Pacific bluefin tuna. Environmental factors were chosen to estimate the recruitment per spawning stock biomass, and a simulation model that well reproduced the spawning stock biomass was developed. Then, effects of various fisheries regulations were evaluated using the simulation study. The results were as follows: 1) arctic oscillations, Pacific decadal oscillations and the recruitment number of the Pacific stock of Japanese sardine were chosen as the environmental factors that determined the recruitment per spawning stock biomass; 2) spawning stock biomass could be well reproduced using a model that reproduced the recruitment per spawning stock biomass and the survival process of the population that included the effect of fishing; and 3) the effects of various fisheries regulation could be evaluated using the simulation model mentioned above. The effective regulation in the simulations conducted in this paper was a prohibition of fishing for 0- and 1-year-old fish in terms of recovering the spawning stock biomass. The reduction of fishing mortality coefficients for all age fish to 50% of actual values also showed a good performance. The recent reductions of the recruitment and spawning stock biomass were likely caused by heavy harvesting, especially of immature fish, since 2004.
Limit of the Principal’s Information  [PDF]
Kazumi Hori
Theoretical Economics Letters (TEL) , 2017, DOI: 10.4236/tel.2017.72018
Abstract: This note characterizes the optimal contract when a principal has unverifiable subjective information that is correlated with an agent’s private information. We find that the principal’s subjective information cannot alleviate the information asymmetry and, moreover, the second best contract is independent from it if the correlation is low.
Comovement of Stock Markets—An Analysis by Nonlinear Cointegration*  [PDF]
Kazumi Asako, Zhentao Liu
Open Journal of Social Sciences (JSS) , 2016, DOI: 10.4236/jss.2016.45010

This paper proposes and estimates a statistical model of nonlinear cointegration, with applications to the stock markets of Japan and the United States. We define nonlinear cointegration as a long-run stable relationship between two time series variables even in the presence of temporary nonlinear divergence from this long-run relationship. More concretely, extending the bubble model of Asako and Liu (2013) [1] to stock price ratio variables, both upward and downward divergent bubble processes are estimated at a time. We conclude that, although two stock price indexes are not linearly cointegrated, they are considered to be cointegrated nonlinearly.

On sequences involving primes
Yukio Ohkubo
Uniform Distribution Theory , 2011,
Abstract: In this paper we give the set of distribution functions of $f(p_n)$ $\bmod 1$ for a special class of functions $f(x)$. Also, we generalize a result on distribution functions shown by O. Strauch and O. Bla eková to a multi-dimensional case. Applying it, we prove that every uniform distributed sequence $x_n$ $\bmod 1$ and $\log p_n$ $\bmod 1$ is statistically independent. By combining this and a result of G. Rauzy we derive that the sequences $p_n\theta +\log p_n$ and $p_n\theta + p_n/n$ are uniformly distributed $\bmod 1$ with irrational $\theta$.
The stochastic pump current and the non-adiabatic geometrical phase
Jun Ohkubo
Physics , 2007, DOI: 10.1088/1742-5468/2008/02/P02011
Abstract: We calculate a pump current in a classical two-state stochastic chemical kinetics by means of the non-adiabatic geometrical phase interpretation. The two-state system is attached to two particle reservoirs, and under a periodic perturbation of the kinetic rates, it gives rise to a pump current between the two-state system and the absorbing states. In order to calculate the pump current, the Floquet theory for the non-adiabatic geometrical phase is extended from a Hermitian case to a non-Hermitian case. The dependence of the pump current on the frequency of the perturbative kinetic rates is explicitly derived, and a stochastic resonance-like behavior is obtained.
Condensation phenomena with distinguishable particles
Jun Ohkubo
Physics , 2007, DOI: 10.1103/PhysRevE.76.051108
Abstract: We study real-space condensation phenomena in a type of classical stochastic processes (site-particle system), such as zero-range processes and urn models. We here study a stochastic process in the Ehrenfest class, i.e., particles in a site are distinguishable. In terms of the statistical mechanical analogue, the Ehrenfest class obeys the Maxwell-Boltzmann statistics. We analytically clarify conditions for condensation phenomena in disordered cases in the Ehrenfest class. In addition, we discuss the preferential urn model as an example of the disordered urn model. It becomes clear that the quenched disorder property plays an important role in the occurrence of the condensation phenomenon in the preferential urn model. It is revealed that the preferential urn model shows three types of condensation depending on the disorder parameters.
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