Advances on CMOS image sensors

This paper offers an introduction to the technological advances of image sensors designed using complementary metal–oxide–semiconductor (CMOS) processes along the last decades. We review some of those technological advances and examine potential disruptive growth directions for CMOS image sensors and proposed ways to achieve them. Those advances include breakthroughs on image quality such as resolution, capture speed, light sensitivity and color detection and advances on the computational imaging. The current trend is to push the innovation efforts even further as the market requires higher resolution, higher speed, lower power consumption and, mainly, lower cost sensors. Although CMOS image sensors are currently used in several different applications from consumer to defense to medical diagnosis, product differentiation is becoming both a requirement and a difficult goal for any image sensor manufacturer. The unique properties of CMOS process allows the integration of several signal processing techniques and are driving the impressive advancement of the computational imaging. With this paper, we offer a very comprehensive review of methods, techniques, designs and fabrication of CMOS image sensors that have impacted or might will impact the images sensor applications and markets

Function of Bmpr1a in ES cell differentiation and cell competition

Bone morphogenetic protein (BMP) 4 signalling via BMPR1A is required for the maintenance of the epiblast in the early embryo, and for self-renewal of pluripotent mouse embryonic stem (ES) cells by inhibiting neural differentiation. In this study, the self-renewal and differentiation abilities of ES cells lacking BMPR1A were investigated. Bmpr1a-null ES cells did not respond to BMP4 but retained a degree of SMAD1/5/8 activation and Id1 expression. This activation was likely due to BMP7 signalling via ACVR1. The observation that Bmpr1a-/- ES cells showed no selfrenewal or pluripotency defects suggested that signalling by BMPs of the 60a subgroup (such as BMP7) can also maintain pluripotency. When Bmpr1a-/- ES cells were differentiated, although they did form derivatives of the three germ layers, they displayed a higher propensity to undergo neurectodermal specification than control cells, likely due to their lower levels of BMP signalling. Cell Competition is the process by which viable cells are eliminated in the presence of metabolically more active or fitter cells. In Drosophila this process depends on dMyc levels and on limiting amounts of the survival factor Decapentaplegic (homologous to the mammalian BMPs). When Bmpr1a-/- ES cells were co-cultured with wild-type cells, they gradually disappeared from the culture and were therefore out-competed. This cell competition was enhanced by limiting the amounts of survival and growth factors and could be rescued by restoring BMP4 signalling in Bmpr1a-/- cells. In co-culture, Bmpr1a-/- ES cells showed no significant changes in apoptosis but had a decreased cell cycle rate and increased levels of differentiation. Concomitantly, higher c-MYC levels were observed in wild-type cells due to increased protein stability. The out-competition of Bmpr1a-/- cells was dependent on differentiation as it could be prevented by inhibiting this process. These results suggest that during development cell competition may be an important mechanism controlling cell fate and survival

General equilibrium with asymmetric information and default penalties

We introduce a two-period general equilibrium model with uncertainty and incomplete financial markets, where default is allowed and agents face in case they do default an utility penalty, which is their own private information. In this setting, if agents have heterogeneous characteristics they will generally pay different returns on any given asset, and thus the same promise made by different agents is in fact not equivalent. If asset trading is anonymous, then the same price is paid for promises whose value can be in fact quite different, and very severe adverse selection problems may arise as consequence. We thus incorporate in the above model an alternative way to negotiate the financial assets, under which an equilibrium exists and the adverse selection problem is mitigated. Succinctly, consumers trade assets non-anonymously with a set of financial intermediaires not allowed to default.Asymmetric information, adverse selection, default penalties, bilateral negotiation, equilibruim.

Smarandache Sequences: Explorations and Discoveries with a Computer Algebra System

Study of Smarandache sequences of numbers, and related problems, via a Computer Algebra. Sy::;tem. Solutions are di::;covered, and some conjectures presented

A Semidefinite Approach to the KiK_i Cover Problem

We apply theta body relaxations to the $K_i$-cover problem and show polynomial time solvability for certain classes of graphs. In particular, we give an effective relaxation where all $K_i$-$p$-hole facets are valid, and study its relation to an open question of Conforti et al. For the triangle free problem, we show for $K_n$ that the theta body relaxations do not converge by $(n-2)/4$ steps; we also prove for all $G$ an integrality gap of 2 for the second theta body

On evolution of CMOS image sensors

CMOS Image Sensors have become the principal technology in majority of digital cameras. They started replacing the film and Charge Coupled Devices in the last decade with the promise of lower cost, lower power requirement, higher integration and the potential of focal plane processing. However, the principal factor behind their success has been the ability to utilise the shrinkage in CMOS technology to make smaller pixels, and thereby have more resolution without increasing the cost. With the market of image sensors exploding courtesy their inte- gration with communication and computation devices, technology developers improved the CMOS processes to have better optical performance. Nevertheless, the promises of focal plane processing as well as on-chip integration have not been fulfilled. The market is still being pushed by the desire of having higher number of pixels and better image quality, however, differentiation is being difficult for any image sensor manufacturer. In the paper, we will explore potential disruptive growth directions for CMOS Image sensors and ways to achieve the same

Convex Hulls of Algebraic Sets

This article describes a method to compute successive convex approximations of the convex hull of a set of points in R^n that are the solutions to a system of polynomial equations over the reals. The method relies on sums of squares of polynomials and the dual theory of moment matrices. The main feature of the technique is that all computations are done modulo the ideal generated by the polynomials defining the set to the convexified. This work was motivated by questions raised by Lov\'asz concerning extensions of the theta body of a graph to arbitrary real algebraic varieties, and hence the relaxations described here are called theta bodies. The convexification process can be seen as an incarnation of Lasserre's hierarchy of convex relaxations of a semialgebraic set in R^n. When the defining ideal is real radical the results become especially nice. We provide several examples of the method and discuss convergence issues. Finite convergence, especially after the first step of the method, can be described explicitly for finite point sets.Comment: This article was written for the "Handbook of Semidefinite, Cone and Polynomial Optimization: Theory, Algorithms, Software and Applications

Students' views of higher education in their transitions to work in Portugal

Higher education has grown to mass proportions in the past two decades in Portugal, with the\ud political expectation that it will contribute to the knowledge economy and social change.\ud However, the predominantly low skilled productive system has led to increasing graduate\ud unemployment and underemployment. The central question in this research is what higher\ud education signifies for students and graduates in this context.\ud Higher education has the potential to change students' relationship with knowledge, developing\ud critical thinking, autonomy and character (Barnett 1990). However, this potential for change\ud depends on how individuals engage in it, according to their values and perspectives (Bloomer\ud 2001). Moreover, knowledge is constructed contextually (Lave and Wenger 1991), and its\ud relevance is not always clear when graduates start work. This longitudinal research therefore\ud consisted of in-depth interviews with graduates to ascertain the meanings and values they\ud attribute to higher education and how this changes in the transition to work.\ud In this study, participants' view of higher education was narrow, focussing on how it affected\ud their labour market opportunities, rather than as a place for personal development, gaining\ud generic skills and critical engagement. This affected how they acted on their educational\ud opportunities and the criteria by which they measured the validity of higher education after their\ud transition to work. Moreover, labour market limitations meant that graduates who did not find\ud work in areas directly related to their degree devalued their education. This study concluded\ud that individual paths from education to work are affected by social networks, resources and\ud significant others, but there are no deterministic effects of social class, gender or field of study.\ud A key finding was that in contrast to Bloomer's concept of learning careers (1997), graduates'\ud embedded knowledge was insufficient for their new work contexts; instead they needed to\ud reconstruct their knowledge according to their socio-cultural resources, and membership of\ud multiple communities. This has significance internationally for research into transitions to work.\ud In general, broader perspectives of higher education by students and employers, greater\ud support for the transition and greater labour market opportunities, would be beneficial for both\ud graduates' self-realization and how mass higher education can affect the knowledge economy