Periodic polymer photonic bandgap structures for on-chip optical cavities

Integrated on-chip optical platforms enable high performance in applications of high-speed all-optical or electro-optical switching, wide-range multi-wavelength on-chip lasing for communication, and lab-on-chip optical sensing. Integrated optical resonators with high quality factor are a fundamental component in these applications. Periodic photonic structures (photonic crystals) exhibit a photonic band gap, which can be used to manipulate photons in a way similar to the control of electrons in semiconductor circuits. This makes it possible to create structures with radically improved optical properties. Compared to silicon, polymers offer a potentially inexpensive material platform with ease of fabrication at low temperatures and a wide range of material properties when doped with nanocrystals and other molecules. In this research work, several polymer periodic photonic structures are proposed and investigated to improve optical confinement and optical sensing. We developed a fast numerical method for calculating the quality factor of a photonic crystal slab (PhCS) cavity. The calculation is implemented via a 2D-FDTD method followed by a post-process for cavity surface energy radiation loss. Computational time is saved and good accuracy is demonstrated compared to other published methods. Also, we proposed a novel concept of slot-PhCS which enhanced the energy density 20 times compared to traditional PhCS. It combines both advantages of the slot waveguide and photonic crystal to localize the high energy density in the low index material. This property could increase the interaction between light and material embedded with nanoparticles like quantum dots for active device development. We also demonstrated a wide range bandgap based on a one dimensional waveguide distributed Bragg reflector with high coupling to optical waveguides enabling it to be easily integrated with other optical components on the chip. A flexible polymer (SU8) grating waveguide is proposed as a force sensor. The proposed sensor can monitor nN range forces through its spectral shift. Finally, quantum dot - doped SU8 polymer structures are demonstrated by optimizing spin coating and UV exposure. Clear patterns with high emission spectra proved the compatibility of the fabrication process for applications in optical amplification and lasing.

Characterizing Internet worm spatial-temporal infection structures

Since the Morris worm was released in 1988, Internet worms continue to be one of top security threats. For example, the Conficker worm infected 9 to 15 million machines in early 2009 and shut down the service of some critical government and medical networks. Moreover, it constructed a massive peer-to-peer (P2P) botnet. Botnets are zombie networks controlled by attackers setting out coordinated attacks. In recent years, botnets have become the number one threat to the Internet. The objective of this research is to characterize spatial-temporal infection structures of Internet worms, and apply the observations to study P2P-based botnets formed by worm infection. First, we infer temporal characteristics of the Internet worm infection structure, i.e., the host infection time and the worm infection sequence, and thus pinpoint patient zero or initially infected hosts. Specifically, we apply statistical estimation techniques on Darknet observations. We show analytically and empirically that our proposed estimators can significantly improve the inference accuracy. Second, we reveal two key spatial characteristics of the Internet worm infection structure, i.e., the number of children and the generation of the underlying tree topology formed by worm infection. Specifically, we apply probabilistic modeling methods and a sequential growth model. We show analytically and empirically that the number of children has asymptotically a geometric distribution with parameter 0.5, and the generation follows closely a Poisson distribution. Finally, we evaluate bot detection strategies and effects of user defenses in P2P-based botnets formed by worm infection. Specifically, we apply the observations of the number of children and demonstrate analytically and empirically that targeted detection that focuses on the nodes with the largest number of children is an efficient way to expose bots. However, we also point out that future botnets may self-stop scanning to weaken targeted detection, without greatly slowing down the speed of worm infection. We then extend the worm spatial infection structure and show empirically that user defenses, e.g. , patching or cleaning, can significantly mitigate the robustness and the effectiveness of P2P-based botnets. To counterattack, we evaluate a simple measure by future botnets that enhances topology robustness through worm re-infection.

Employee perceptions of workplace empowerment in relation to self -reported intent to stay on the job

As the nursing profession faces a shortage of nurses, workplace initiatives focused on retaining employees are critical to the United States healthcare industry (Sochalski, 2002). The purpose of this research was to determine whether self-reported intent to stay on the job was related to perceptions of workplace empowerment using Kanter's (1977) theory of organizational empowerment as a framework. ^ The sample consisted of 206 Florida registered nurses. Four self-report scales and a demographic questionnaire were administered by mail. The Conditions for Work Effectiveness Questionnaire (CWEQ; Chandler, 1987), Job Activity Scale (JAS; Laschinger, Kutzscher, & Sabiston, 1993), Organizational Relationships Scale (ORS; Laschinger, Sabiston, & Kutzscher, 1993) and an intent to stay instrument (Kim, Price, Mueller & Watson, 1996) were used to measure perceived access to empowerment structures, perceived formal power, perceived informal power, and intent to stay, respectively. The data were analyzed using descriptive statistics, correlational analysis, and hierarchical regression. ^ Twenty-eight percent of the variance of intent to stay was explained by perceived access to empowerment structures, perceived formal power, and perceived informal power when holding age, gender, education, overall nursing experience, and number of years on current job constant. Perceived access to empowerment structures (CWEQ total score) was the best predictor of self-reported intent to stay for this sample. Of the four components of perceived access to work empowerment structures, perceived access to opportunity and resources were the best predictors of nurses' intent to stay on the job. ^ This study was the first step in establishing the relationship between Kanter's full model and intent to remain on the job, which is a stepping stone for the development of effective retention strategies based on a workplace empowerment model. This knowledge is particularly important in today's healthcare industry where healthcare administrators and human resource development practitioners are ideally positioned to implement organizational strategies to enhance access to work empowerment structures and potentially reduce turnover and mitigate the effects of nursing shortage. ^