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In response to how they are compensated, mutual fund managers who are underperforming by mid-year are likely to increase the risk of their portfolios toward the year-end. We argue that an increase in the liquidity of the stocks that managers use to shift risk can lead to an increase in the size of their risky bets. This in turn hurts fund investors by increasing the costs of misaligned incentives associated with delegated portfolio management. We provide both theoretical and empirical results that are consistent with this argument. We use decimalization as an exogenous shock to liquidity to identify causal effects.
Owing to lack of a definitive correlation between carbon supports and catalytic activity of single-atom Fe-active sites, rational design and preparation of single-atom Fe catalysts have so far been elusive. Herein we designed and prepared one-dimensional core–shell nanostructured single-atom Fe catalysts, in which carbon nanofibers and carbon nanotubes with different crystallinities and electrical conductivities were used as supports to host single-atom Fe-active sites. It was found that the carbon supports with higher electrical conductivity accelerate charge transfer and enhance the oxygen reduction reaction (ORR) activity of single-atom Fe-active sites as well as the ORR durability of the final catalyst.
The semilocal convergence of a third-order Newton-like method for solving nonlinear equations is considered. Under a weak condition (the so-called γ-condition) on the derivative of the nonlinear operator, we establish a new semilocal convergence theorem for the Newton-like method and also provide an error estimate. Some numerical examples show the applicability and efficiency of our result, in comparison to other semilocal convergence theorems.
Many real-world problems are known as planning and scheduling problems, where resources must be allocated so as to optimize overall performance objectives. The traditional scheduling models consider performance indicators such as processing time, cost, and quality as optimization objectives. However, most of them do not take into account energy consumption and robustness. We focus our attention in a job-shop scheduling problem where machines can work at different speeds. It represents an extension of the classical job-shop scheduling problem, where each operation has to be executed by one machine and this machine can work at different speeds. The main goal of the paper is focused on the analysis of three important objectives (energy efficiency, robustness, and makespan) and the relationship among them. We present some analytical formulas to estimate the ratio/relationship between these parameters. It can be observed that there exists a clear relationship between robustness and energy efficiency and a clear trade-off between robustness/energy efficiency and makespan. It represents an advance in the state of the art of production scheduling, so obtaining energy-efficient solutions also supposes obtaining robust solutions, and vice versa.
In this study, a novel hybrid block copolymer containing POSS (BCP), poly(methacrylisobutyl-POSS)-b-poly(methylmethacrylate) (PMAiBuPOSS-b-PMMA) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The structure and molecular weight were characterized via 1H NMR and GPC. BCP was creatively used as the compatibilizer to overcome the bad compatibility of epoxy and POSS in their blend system. SEM and dynamic mechanical thermal analyses (DMTA) were used to observe the surface morphology and thermal–mechanical behaviors of the resultant products. We found that the amount of microaggregation domains of POSS decreased, while the nano ones increased, when BCP content increased. All the aggregation domains were distributed in epoxy matrix uniformly at nanoscale with the addition of 10 phr BCP and 5 phr POSS monomers. The results indicated that BCP could effectively improve the compatibility between epoxy resin and POSS owing to its amphiphilicity in DGEBA. The fracture behavior of products transformed from brittle fracture to ductile fracture gradually with the increase of BCP, whereas the Tg and E′ decreased.
Kashin-Beck disease (KBD) is a chronic endemic osteoarthropathy, which mainly occurs in West and Northeast China. Epidemiological studies suggest that Se deficiency is an important environmental factor for the incidence of KBD. Glutathione peroxidase 4 (GPx4) belongs to the glutathione peroxidase family, which is crucial for optimal antioxidant defences. Our purpose is to investigate the putative association between GPx4 polymorphisms and the risk of KBD. Restriction fragment length polymorphism-PCR was used to detect two SNP (rs713041, rs4807542) in 219 cases and 194 controls in Han Chinese subjects, and quantitative analysis for the GPx4 mRNA level was performed by the real-time PCR method. The results revealed that linkage disequilibrium existed in the two SNP. A significant difference was observed in the haplotype A-T (P = 0·0066) of GPx4, which was obviously lower in the KBD cases (0·006 v. 0·032 %). Correlation analysis based on a single locus showed no association between each SNP and KBD risk. Furthermore, the GPx4 mRNA level was dramatically lower in the blood of KBD patients. Overall, our finding indicated GPx4 polymorphisms and decreased mRNA level may be related to the development of KBD in the Chinese population, suggesting GPx4 as a possible candidate susceptibility gene for KBD.
We describe the biosynthesis and characterization of protein materials
comprised of two distinct self-assembling domains (SADs): elastin (E) found
in tissue for its elastic properties and cartilage oligomeric matrix protein
coiled-coil (COMPcc, C) predominantly locatedin joint and in bones. Based on
earlier studies on protein block polymers comprised these two SADs,
orientation and number of blocks play a crucial role in the overall
stimuli-responsive supramolecular assembly behavior. Here we fabricate a
range of EnC and CEn block polymers in which the E
domain is systematically truncated to explore the effects of the E domain on
the overall physicochemical behavior.
In 1995, the first author of this book joined Victoria University. Immediately after that, he established a new research group called the Optoelectronic Imaging Group (OIG), with a focus on the introduction of femtosecond lasers into optical microscopy. While the first two-photon fluorescence microscope was reported in 1990, it was not until 1996 that the first two-photon fluorescence microscope in Australia was constructed by a group of OIG Ph.D. students with a femtosecond laser supported by the major equipment fund of Victoria University. It was this new instrument that gave the OIG research students and staff a powerful tool to conduct biophotonic research. At the beginning of 2000, most of the OIG members moved to Swinburne University of Technology to form a new research centre called the Centre for Micro-Photonics (CMP). Since 1995, research students of the OIG and the CMP, including four of the authors of the book, Damian Bird, Daniel Day, Ling Fu and Dru Morrish, have made many significant contributions to femtosecond biophotonic methods. The aim of this book is to provide a systematic introduction into these methods. Chapters 1–3, 6 and 8 were completed by Min Gu and Chapters 4, 5, 7 and 9 were written by Damian Bird, Ling Fu, Dru Morrish and Daniel Day, respectively. All the authors participated in the final editing of the book.
In this chapter, we introduce a new trapping and excitation technique, which utilises a single femtosecond pulse infrared illumination source to simultaneously trap and excite a microsphere probe. The induction of morphology dependent resonance (MDR) in the trapped probe is achieved under two-photon excitation. Monitoring of the MDR in the trapped probe provides a contrast mechanism for imaging and sensing. The experimental measurement of MDR within a laser trapped microsphere excited under two-photon absorption is confirmed in Section 7.2. The effect of the laser power as well as the pulse width on the transverse trapping force is investigated in Section 7.3. The dependence of two-photon induced MDR on the scanning velocity of a trapped particle is then experimentally determined. These parameters are fundamental to the acquisition of images and sensing with femtosecond laser tweezers as described in Section 7.4.
Laser trapping is an ideal method for the remote, non-invasive manipulation of a morphology dependent resonance microcavity. Controlled scanning and manipulation of the microcavity is possible via laser trapping. The microcavity has an enhanced evanescent field at its surface due to the resonant circumferential propagation of radiation at glancing angles greater than the critical angle. Freely suspended in a medium, the cavity becomes increasingly sensitive to its surrounding environment. The interaction of the cavity with its local environment during scanning dynamically alters the coupling to and leakage from the cavity. Monitoring the change in coupling to and leakage from the cavity over time enables imaging and sensing.
As discussed in Chapters 1 and 2, biological tissue is a highly scattering medium which will affect image resolution, contrast and signal level. This chapter discusses the effect of multiple scattering in a tissue-like turbid medium on two-photon fluorescence microscopy. Section 3.1 discusses a model based on imaging of microspheres embedded in a turbid medium. A quantitative study of the limiting factors on image quality is given in Section 3.2. In particular, the limitation on the penetration depth in turbid media, revealed from Monte-Carlo simulation and experimental measurements, is presented in Section 3.3.
Two-photon fluorescence microscopy of microspheres embedded in turbid media
Two-photon fluorescence microscopy has been extensively used due to its significant advantages over single-photon fluorescence microscopy. This technology has been used for in vivo imaging of thick biological samples. Since the required image information is taken at a large depth within a biological specimen, optical multiple scattering within tissue may result in a severe distortion on images obtained in this situation. Thus, the effect of optical multiple scattering on fluorescence image quality should be understood if high quality images are to be obtained at significant depths into a biological specimen. In this section, we present measured images of small fluorescent microspheres embedded in a turbidmedium which has different scattering characteristics under singlephoton and two-photon excitation. Imaging of small spheres embedded in a turbid medium has practical importance since it can be considered to be an approximate model of imaging small tumours embedded in biological tissue.
Ever since researchers realised that microscopy based on nonlinear optical effects can provide information that is blind to conventional linear techniques, applying nonlinear optical imaging to in vivo medical diagnosis in humans has been the ultimate goal. The development of nonlinear optical endoscopy that permits imaging under conditions in which a conventional nonlinear optical microscope cannot be used is the primary method to extend applications of nonlinear optical microscopy toward this goal. Fibreoptic approaches that allow for remote delivery and collection in a minimally invasive manner are normally used in nonlinear optical endoscopy. In Chapter 4, a compact nonlinear optical microscope based on a single-mode fibre (SMF) coupler to replace complicated bulk optics was described.
There are several key challenges involved in the pursuit of in vivo nonlinear optical endoscopy. First, an excitation laser beam with an ultrashort pulse width should be delivered efficiently to a remote place where efficient collection of faint nonlinear optical signals from biological samples is required. Second, laser-scanning mechanisms adopted in such a miniaturised instrumentation should permit size reduction to a millimetre scale and enable fast scanning rates for monitoring biological processes. Finally, the design of a nonlinear optical endoscope based on micro-optics must maintain great flexibility and compact size to be incorporated into endoscopes to image internal organs.
The techniques introduced in Chapters 1 and 2 are emerging technologies that offer significant promise as tools for diagnostic imaging at the cellular level. Using devices founded on well established techniques such as confocal microscopy and confocal fluorescence microscopy, instruments capable of providing point-of-care pathological analysis of malignant and cancer causing tissues are becoming practical realities. Through examination of the physical properties of inherent autofluorescence or fluorescent dyes that are used as markers in conjugation with biological samples, very good detection of cellular processes can be achieved. Tagging of target biological cells makes it possible to examine cells in vivo and achieve real time three-dimensional (3D) visualisation for diagnosis of the pathological state.
However, the inherent nature of these devices is such that the conditions under which these techniques can be applied is fundamentally limited. In most cases (for definitive analysis) a surgical biopsy is performed on the patient and the sample is extensively prepared for observation by the pathologist on bulk, bench-top imaging apparatus. Ideally, examination of whole, intact specimens within internal cavities of the body would be the preferred method that may decrease patient trauma and eliminate diagnosis lag time.
One of the recent developments in confocal fluorescence microscopy is the introduction of optical fibres and fibre-optical components into the microscope geometry. Optical fibre couplers in particular offer the most compact and cost effective solution.
As discussed in Chapter 6, the trapping volume of a far-field laser trapping geometry is approximately three times larger in the axial direction than that in the transverse direction. Such trapping volume elongation leads to a significant background and poses difficulties in the observations of nano-particle dynamics. In this chapter, we deal with near-field optics using focused evanescent illumination. The recent development of near-field optical tweezers is reviewed in Section 8.1. Section 8.2 introduces the new concept of near-field laser tweezing with a focused evanescent field. This technology is characterised both experimentally and theoretically in Section 8.3. Section 8.4 presents the utilisation of a femtosecond laser beam in a near-field optical trap. Finally, some discussions on this new method are given in Section 8.5.
Near-field optical tweezers
Near-field laser trapping or tweezers means that radiation force that is used for trapping and manipulating a micro-object results from the interaction with an evanescent wave. Recently, a new trapping modality based on the evanescent wave illumination, also called near-field illumination, has been proposed and demonstrated. This trapping technique results in a significantly reduced trapping volume due to the fact that the strength of an evanescent wave decays rapidly with the distance from the surface at which the field is generated. In this section, the near-field trapping mechanism based on the different ways to generate a localised near-field is reviewed.
This chapter serves as an introduction to this book. Section 1.1 gives a brief review on the development of biophotonics and summarises the main achievements in biophotonics due to the introduction of femtosecond pulse lasers, while Section 1.2 defines the scope of the book.
Biophotonics involves the utilisation of photons, quanta of light, to image, sense and manipulate biological matter. It provides the understanding of the fundamental interaction of photons with biological media and the application of this understanding in life sciences including biological sciences and biomedicine. In that sense, biophotonics research dates back to times when biologists started to use optical microscopy and spectroscopy with a conventional light source such as a lamp. These two forms of classic biophotonic instrument revolutionised biological research and are the classic bridge between photonics and life sciences because they provide a non-destructive way to view the two-dimensional (2D) microscopic world that human eyes cannot, as well as the function of microscopic samples through colour or spectroscopic information.
Biophotonics became a recognised new discipline after the laser was invented in 1960. Laser light is fundamentally different from conventional light in the sense that it possesses high brightness in a narrow spectral window, is highly directional, and exhibits a high degree of coherence. Since 1960, these unique features have facilitated many important applications of laser technology in biological and biomedical studies. One of the important milestones in this area is the combination of laser light with an optical microscope, which led to laser scanning confocal microscopy.
The aim of this chapter is to provide a comprehensive understanding of trapped-particle near-field scanning optical microscopy (NSOM). The principle of optical trapping and laser tweezers is briefly explained in Section 6.1. Section 6.2 summarises the motivation of using a laser-trapped microsphere as a probe in NSOM. The basic principle of trapped-particle NSOM is described in Section 6.3. Two major aspects of this technique, laser trapping performance and near-field Mie scattering of dielectric and metallic particles, are discussed in Sections 6.4 and 6.5, respectively. Experimental results on image formation in trapped-particle NSOM are described in Section 6.6. In Section 6.7, some prospects for the future development of this technique are put forward.
Optical trapping and laser tweezers
Photons carry momentum. When the change in momentum occurs upon reflection, refraction, transmission and absorption of a light beam, the rate of change of momentum results in a force being exerted on an object. The origin of this force can be understood from Newton's laws. A light ray that is refracted through a dielectric particle changes its direction due to the refraction process. Since light carries momentum, a change in light direction implies that there must exist a force associated with that change. The resulting force, manifested as a recoil action due to the momentum redirection, draws mesoscopic particles toward the highest photon flux in the focal region. This recoil is unnoticeable for refraction by macroobjects such as lenses, but it has a substantial and measurable influence on mesoscopic refractive objects such as small dielectric particles.
The introduction of femtosecond pulse lasers has provided numerous new methods for non-destructive diagnostic analysis of biological samples. This book is the first to provide a focused and systematic treatment of femtosecond biophotonic methods. Each chapter combines theory, practice and applications, walking the reader through imaging, manipulation and fabrication techniques. Beginning with an explanation of nonlinear and multiphoton microscopy, subsequent chapters address the techniques for optical trapping and the development of laser tweezers. In a conclusion that brings together the various topics of the book, the authors discuss the growing field of femtosecond micro-engineering. The wide range of applications for femtosecond biophotonics means this book will appeal to researchers and practitioners in the fields of biomedical engineering, biophysics, life sciences and medicine.