On the Stanley Depth of Squarefree Veronese Ideals

Let $K$ be a field and $S=K[x_1,...,x_n]$. In 1982, Stanley defined what is now called the Stanley depth of an $S$-module $M$, denoted \sdepth(M), and conjectured that \depth(M) \le \sdepth(M) for all finitely generated $S$-modules $M$. This conjecture remains open for most cases. However, Herzog, Vladoiu and Zheng recently proposed a method of attack in the case when $M = I / J$ with $J \subset I$ being monomial $S$-ideals. Specifically, their method associates $M$ with a partially ordered set. In this paper we take advantage of this association by using combinatorial tools to analyze squarefree Veronese ideals in $S$. In particular, if $I_{n,d}$ is the squarefree Veronese ideal generated by all squarefree monomials of degree $d$, we show that if $1\le d\le n < 5d+4$, then \sdepth(I_{n,d})= \floor{\binom{n}{d+1}\Big/\binom{n}{d}}+d, and if $d\geq 1$ and $n\ge 5d+4$, then d+3\le \sdepth(I_{n,d}) \le \floor{\binom{n}{d+1}\Big/\binom{n}{d}}+d.Comment: 10 page

Cavitation scaling experiments with headforms : bubble dynamics

Utilizing some novel instrumentation which allowed detection and location of individual cavitation bubbles in flows around headforms. Ceccio and Brennen (1991 and 1989) recently examined the interaction between individual bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. More recently Kumar and Brenncn (1991-1992) have closely examined further statistical properties of the acoustical signals from individual cavitation bubbles on two different headformsm in order to learn more about the bubble/flow interactions. However the above experiments were all conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified in those earlier experiments change with changes of speed, scale and facility. The present paper will describe experiments conducted in order to try to answer some of these important qucstions regarding the scaling of the cavitation phenomena. We present data from experiments conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis, Tennessee, on similar headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers. In this paper we focus on visual observations of the cavitation patterns and changes in these patterns with speed and headform size

Cavitation Scaling Experiments with Axisymmetric Bodies

Several experiments by Ceccio and Brennen (1991, 1989) and Kumar and Brennen (1992, 1991) have closely examined the interaction between individual cavitation bubbles and the boundary layer, as well as statistical properties of the acoustical signals produced by the bubble collapse. All of these experiments were, however, conducted in the same facility with the same headform size (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper describes experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. The experiments were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on geometrically similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers

Presenilins are required for maintenance of neural stem cells in the developing brain

The early embryonic lethality of mutant mice bearing germ-line deletions of both presenilin genes precluded the study of their functions in neural development. We therefore employed the Cre-loxP technology to generate presenilin conditional double knockout (PS cDKO) mice, in which expression of both presenilins is inactivated in neural progenitor cells (NPC) or neural stem cells and their derivative neurons and glia beginning at embryonic day 11 (E11). In PS cDKO mice, dividing NPCs labeled by BrdU are decreased in number beginning at E13.5. By E15.5, fewer than 20% of NPCs remain in PS cDKO mice. The depletion of NPCs is accompanied by severe morphological defects and hemorrhages in the PS cDKO embryonic brain. Interkinetic nuclear migration of NPCs is also disrupted in PS cDKO embryos, as evidenced by displacement of S-phase and M-phase nuclei in the ventricular zone of the telencephalon. Furthermore, the depletion of neural progenitor cells in PS cDKO embryos is due to NPCs exiting cell cycle and differentiating into neurons rather than reentering cell cycle between E13.5 and E14.5 following PS inactivation in most NPCs. The length of cell cycle, however, is unchanged in PS cDKO embryos. Expression of Notch target genes, Hes1 and Hes5, is significantly decreased in PS cDKO brains, whereas Dll1 expression is up-regulated, indicating that Notch signaling is effectively blocked by PS inactivation. These findings demonstrate that presenilins are essential for neural progenitor cells to re-enter cell cycle and thus ensure proper expansion of neural progenitor pool during embryonic neural development

Development and Evaluation of Wearable Inertial Sensing Techniques for Magnetometer-Free Spacesuit Wearer Joint Kinematics Estimation

The design of future EVA spacesuits seeks to reduce the risk and incidence of injury while working in the suit, which requires quantitative observations of human motion inside the suit. Past efforts using wearable IMUs to study human motion inside spacesuits have been unable to achieve sufficient accuracy for informing spacesuit design. These past approaches have relied on magnetometers for heading correction, which have been shown to be unreliable for measuring heading indoors. Furthermore, hardware used in these past efforts were susceptible to failure in the harsh in-suit environment, and the impact of the devices on wearer comfort, mobility, and movement strategies was not characterized. This thesis investigates potential solutions to these shortcomings and is broadly divided into three parts. First, the research investigates techniques and error sources for magnetometer-free inertial sensing of human motion to inform the development of an in-house wearable IMU system for human motion capture inside spacesuits. It was found that, contrary to what is commonly suggested in the literature, numerical integration error, rather than sensor noise, is the dominant contributor to drift in inertial sensing of human motion using currently available low-cost sensors. The work also found that a two-speed attitude integration architecture was an effective way to reduce numerical integration error by sampling the sensors at a high rate while keeping data processing, throughput, and storage requirements moderate. Based on these findings, a configuration was chosen for the hardware architecture and attitude estimation algorithm of the wearable system, and the attitude estimation performance of the chosen configuration was found in simulation to be sufficient for informing spacesuit design. Second, a novel low-cost technique for calibrating inertial sensors for biomechanics applications was developed. The technique combines two nontraditional calibration approaches, namely the static orientations approach and the optical motion capture approach. It was found that the combined approach produces calibration parameters that are generally more accurate than either approach alone and with greater certainty. Moreover, the technique is capable of calibrating inertial sensors over a range of measurements relevant to human motions, which traditional calibrations are sometimes unable to achieve, potentially making it more attractive than a traditional calibration for biomechanical applications. Finally, the wearable IMU system was fabricated, calibrated, and evaluated. It was found that the system had no significant impact on wearer comfort and mobility while working inside a pressurized spacesuit arm. The current research represents the first published effort to evaluate the effect of wearable sensors on suited comfort and mobility. The system was found to be capable of surviving mechanical loads corresponding to multiple in-suit testing sessions under highly conservative conditions. The limb segment attitude estimation performance of the system was demonstrated to be superior or similar to past work over comparable time scales, but analysis over longer time scales revealed hardware deficiencies not captured in simulations. The results of the current work nonetheless demonstrate that once these deficiencies are overcome, the methods developed in this research can be applied successfully for accurate human motion capture inside spacesuits and other operational environments. The outcomes of the current research represent a significant step forward in the development of capabilities for quantitative analysis of human-spacesuit interaction. Such capabilities will allow safer spacesuits to be designed more efficiently, the availability of which is increasingly important as future human space exploration programs that rely heavily on EVA and take place in increasingly remote destinations take shape. More generally, the research advances the state of the art in inertial sensing of human motion over extended periods of time in ambulatory environments. Other applications of this work include human motion capture for workplace ergonomics or physical therapy evaluations outside of the confines of a clinic or laboratory.</p

What Drives Consumers in China to Buy Clothing Online? Application of the Technology Acceptance Model

An enormous number of Internet users have made China a profitable e-commerce marketplace, and clothing is one of the most frequently purchased items. This study explores the predictors of consumers’ motivation to buy clothing online in China by extending the technology acceptance model. Data were collected via an online questionnaire, resulting in 504 returned responses. The results indicate that perceived usefulness has a significant effect on consumers’ intention to buy clothing online; however, no direct relationship between perceived ease of use and buying intention was found. Furthermore, perceived convenience, perceived money saving, and perceived time-saving can explain why consumers perceive buying clothing online as useful, and these perceptions have positive effects on buying intention. Additionally, the findings imply that fashion innovativeness and friend circles significantly influence consumers’ intention to purchase clothing online. This article discusses the results and provides recommendations for implication and future research

Nonparametric Independent Component Analysis for the Sources with Mixed Spectra

Independent component analysis (ICA) is a blind source separation method to recover source signals of interest from their mixtures. Most existing ICA procedures assume independent sampling. Second-order-statistics-based source separation methods have been developed based on parametric time series models for the mixtures from the autocorrelated sources. However, the second-order-statistics-based methods cannot separate the sources accurately when the sources have temporal autocorrelations with mixed spectra. To address this issue, we propose a new ICA method by estimating spectral density functions and line spectra of the source signals using cubic splines and indicator functions, respectively. The mixed spectra and the mixing matrix are estimated by maximizing the Whittle likelihood function. We illustrate the performance of the proposed method through simulation experiments and an EEG data application. The numerical results indicate that our approach outperforms existing ICA methods, including SOBI algorithms. In addition, we investigate the asymptotic behavior of the proposed method.Comment: 27 pages, 10 figure