Navigating turbulent waters : crafting learning trajectories in a changing work context

How do newcomers gain access to learning opportunities when they are denied opportunities to practice? Changes in the nature of work, such as labour outsourcing and technological advancements, have created challenges for newcomers to learn. They may be more easily relegated to low-level repetitive tasks, such as scutwork. In these situations, newcomers’ ambiguous position as learners can limit access to participation in practices needed to progress their learning trajectories. Using field-study data, we explore the situated learning of merchant-navy cadets. We show that, when newcomers are not permitted access to participation, the structural arrangements of practice – temporal structures, spatial territories and hierarchical arrangements – hinder learning opportunities. We show, further, that some newcomers leverage these same structural arrangements surreptitiously as resources to access participation, which we conceptualise as stealth work. Consequently, we unveil the soft forms of power at play in crafting access to learning trajectories, making three contributions. First, we show how structural arrangements of a practice can be leveraged to enable learning. Second, we show that gaining access stealthily, requires both normative and counter-normative performances. Third, we show the importance of access in crafting learning trajectories and unpack how such access is navigated by newcomers

Nitrogen incorporation and optical studies of GaAsSbN/GaAs single quantum weil heterostructures

Cataloged from PDF version of article.In this work, the effects of N incorporation on the optical properties of GaAsSbN/GaAs single quantum wells (SQWs) have been investigated using temperature, excitation, and magnetic dependencies of photoluminescence (PL) characteristics. These layers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma N source. The N concentrations in the range of 0.5%-2.5% were investigated in this study. The SQW with N similar to 0.5% exhibits a behavior similar to that in an intermediate regime where the contributions from the localized states in the band gap are dominant. The temperature and excitation dependencies of the PL characteristics indicate that for the N concentration of 0.9% and above, the alloy behavior is analogous to that of a regular alloy and the changes in optical properties are only marginal. The conduction band effective mass (m(eff)) values computed from the magnetophotoluminescence spectra using a variational formalism and the band anticrossing model are in good agreement and indicate enhanced values of m(eff). However, there is no significant variation in m(eff) values of QWs for N >= 0.9%. Small redshift of about 30-50 meV for the temperature variations from 10 to 300 K in conjunction with unusually small blueshift observed in the excitation dependence of PL for N >= 0.9% indicate that this system holds a great promise for laser applications at 1.55 mu m and beyond

Optical studies of molecular beam epitaxy grown GaAsSbNGaAs single quantum well structures

In this work, the authors present a systematic study on the variation of the structural and the optical properties of GaAsSbNGaAs single quantum wells (SQWs) as a function of nitrogen concentration. These SQW layers were grown by the solid source molecular beam epitaxial technique. A maximum reduction of 328 meV in the photoluminescence (PL) peak energy of GaAsSbN was observed with respect to the reference GaAsSb QW. 8 K and RT PL peak energies of 0.774 eV (FWHM of ∼25 meV) and 0.729 eV (FWHM of ∼67 meV) (FWHM denotes full width at half maximum) corresponding to the emission wavelengths of 1.6 and 1.7 μm, respectively, have been achieved for a GaAsSbN SQW of N∼1.4%. The pronounced S -curve behavior of the PL spectra at low temperatures is a signature of exciton localization, which is found to decrease from 16 to 9 meV with increasing N concentration of 0.9%-2.5%. The diamagnetic shift of 13 meV observed in the magnetophotoluminescence spectra of the nitride sample with N∼1.4% is smaller in comparison to the value of 28 meV in the non-nitride sample, indicative of an enhancement in the electron effective mass in the nitride QWs. Electron effective mass of 0.065 mo has been estimated for a SQW with N∼1.4% using the band anticrossing model. © 2007 American Vacuum Society

Cancer Screening by Systemic Administration of a Gene Delivery Vector Encoding Tumor-Selective Secretable Biomarker Expression

Cancer biomarkers facilitate screening and early detection but are known for only a few cancer types. We demonstrated the principle of inducing tumors to secrete a serum biomarker using a systemically administered gene delivery vector that targets tumors for selective expression of an engineered cassette. We exploited tumor-selective replication of a conditionally replicative Herpes simplex virus (HSV) combined with a replication-dependent late viral promoter to achieve tumor-selective biomarker expression as an example gene delivery vector. Virus replication, cytotoxicity and biomarker production were low in quiescent normal human foreskin keratinocytes and high in cancer cells in vitro. Following intravenous injection of virus >90% of tumor-bearing mice exhibited higher levels of biomarker than non-tumor-bearing mice and upon necropsy, we detected virus exclusively in tumors. Our strategy of forcing tumors to secrete a serum biomarker could be useful for cancer screening in high-risk patients, and possibly for monitoring response to therapy. In addition, because oncolytic vectors for tumor specific gene delivery are cytotoxic, they may supplement our screening strategy as a “theragnostic” agent. The cancer screening approach presented in this work introduces a paradigm shift in the utility of gene delivery which we foresee being improved by alternative vectors targeting gene delivery and expression to tumors. Refining this approach will usher a new era for clinical cancer screening that may be implemented in the developed and undeveloped world

The process of transition : becoming legitimate peripheral participants in the practice of seafaring.

My thesis seeks to develop the theory of legitimate peripheral participation by focusing on how it is accomplished in practice, through exploring the process of transition from novices to (relative) masters. In doing so, the study opens the black box of participation in studies of situated learning and focuses on two aspects that lead to a further development of legitimate peripheral participation. First, it looks at how newcomers undergo legitimate peripheral participation at two sites of practice and how movement between the sites influences the process of transition. Second, it focuses on the ways in which newcomers negotiate access to participation at a site where such access is not readily available. The research was conducted as a five-month multi-sited ethnographic study in the maritime industry; as such it focuses on the process of transition from cadets (newcomers) to officers (relative old-timers). Two research sites were used for conducting the ethnographic study, a maritime training center, and a merchant shipping vessel. Analysis of the data collected through observations and interviews at the two sites reveals key insights into the practical accomplishment of legitimate peripheral participation. The study shows the influence of movement between sites of practice and theorizes transition as an episodic process. Furthermore, the study explores the ways of doing through which newcomers are able to successfully negotiate access to participation. As such it develops a practice-sensitive concept of proactivity as a way of negotiating access to participation. Overall the thesis develops a more nuanced understanding of participation and shows how legitimate peripheral participation is accomplished in practice

Nitrogen incorporation and optical studies of GaAsSbN/GaAs single quantum well heterostructures

In this work, the effects of N incorporation on the optical properties of GaAsSbNGaAs single quantum wells (SQWs) have been investigated using temperature, excitation, and magnetic dependencies of photoluminescence (PL) characteristics. These layers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma N source. The N concentrations in the range of 0.5%-2.5% were investigated in this study. The SQW with N∼0.5% exhibits a behavior similar to that in an intermediate regime where the contributions from the localized states in the band gap are dominant. The temperature and excitation dependencies of the PL characteristics indicate that for the N concentration of 0.9% and above, the alloy behavior is analogous to that of a regular alloy and the changes in optical properties are only marginal. The conduction band effective mass (meff) values computed from the magnetophotoluminescence spectra using a variational formalism and the band anticrossing model are in good agreement and indicate enhanced values of meff. However, there is no significant variation in meff values of QWs for N0.9%. Small redshift of about 30-50 meV for the temperature variations from 10 to 300 K in conjunction with unusually small blueshift observed in the excitation dependence of PL for N0.9% indicate that this system holds a great promise for laser applications at 1.55 μm and beyond. © 2007 American Institute of Physics

Spring-time enhancement in aerosol burden over a high-altitude location in western trans-Himalaya: results from long-term observations

Long-term measurements (from August 2009 to December 2014) of aerosol black carbon mass concentration (MBC) and spectral aerosol optical depth (AOD) were carried out from a high-altitude location, Hanle in western trans-Himalaya as part of the Regional Aerosol Warming Experiment. Both MBC and AOD showed distinct annual pattern with a clear spring-time enhancement (April-June) with significant inter-annual variability associated with the changes in source processes. The potential source regions contributing to the spring-time enhancement in aerosol loading are the dust-dominated west Asian region as well as biomass burning from NW India. The overall annual mean value of MBC over Hanle is extremely low compared to many other Himalayan locations, including the Ganges Valley Aerosol Experiment campaign site at Nainital, which also showed spring-time (pre-monsoon) enhancement. The vertical extents of elevated aerosol layers, which contribute to the spring-time enhancement, are found to be in the range 5-7 km amsl from the analysis of vertical profiles of extinction coefficients from CALIPSO data