On the performance of single-layered neural networks

This paper studies the performance of single-layered neural networks. This study begins with the performance of single-layered neural networks trained using the outer-product rule. The outer-product rule is a suboptimal learning scheme, resulting under certain assumptions from optimal least-squares training of single-layered neural networks with respect to their analog output. Extensive analysis reveals the improvement on the network performance caused by its optimal least-squares training. The effect of the training scheme on the performance of single-layered neural networks with binary output is exhibited by experimentally comparing the performance of single-layered neural networks trained with respect to their analog and binary output.     

A mutant of the green alga Dunaliella salina constitutively accumulates zeaxanthin under all growth conditions

A novel mutant (zea1) of the halotolerant unicellular green alga Dunaliella salina is impaired in the zeaxanthin epoxidation reaction, thereby lacking a number of the beta-branch xanthophylls. HPLC analysis revealed that the zea1 mutant lacks neoxanthin (N), violaxanthin (V) and antheraxanthin (A) but constitutively accumulates zeaxanthin (Z). Under low-light physiological growth conditions, the zea1 (6 mg Z per g dry weight or 8 x 10(-16) mol Z/cell) had a substantially higher Z content than the wild type (0.2 mg Z per g dry weight or 0.5 x 10(-16) mol Z/cell). Lack of N, V, and A did not affect photosynthesis or growth of the zea1 strain. Biochemical analyses suggested that Z constitutively and quantitatively substitutes for N, V, and A in the zea1 strain. This mutant is discussed in terms of its commercial value and potential utilization by the algal biotechnology industry for the production of zeaxanthin, a high-value bioproduct.     

Comparison of C-erbB2 (HER-2/Neu) immunohistochemistry results on invasive breast carcinomas. Experience of 2 Pathology departments in Turkey and Greece

OBJECTIVE: To compare c-erbB2 (HER-2/Neu) immunohistochemical staining results obtained in 2 pathology departments and evaluate the reproducibility of staining and assessments. STUDY DESIGN: Ninety primary invasive ductal carcinoma cases constituted the material of this study. For concordant assessment, serial sections from the same tissue blocks were prepared in both Turkey and Greece and were sent to each other. Evaluation of c-erbB2 (HER-2/Neu) staining was done independently in 2 departments by experienced pathologists. Stained slides were evaluated semiquantitatively in Turkey and both semiquantitatively and automatically in Greece. RESULTS: There was complete agreement on staining density in 58 (64.4%) cases in both centers. In 15 cases there were major discordances in staining degrees, and in 17 cases there was a major discordance. Hypothetical treatment decisions based on these results showed that 82% of patients would have been handled the same way. CONCLUSION: Comparison of immunostaining patterns performed at 2 centers provided valuable data that may be used in the development of quality assurance policies. The present study showed the usefulness of multicenter comparative studies in initiating the development of guidelines.     

Microalgal biotechnology: Carotenoid production by the green algae<Emphasis Type="Italic">Dunaliella salina</Emphasis>

Unicellular green algae of the genusDunaliella thrive in extreme environmental conditions such as high salinity, low pH, high irradiance and subzero temperatures. Species ofDunaliella are well known in the alga biotechnological industry and are employed widely for the production of valuable biochemicals, such as carotenoids. Some strains ofDunaliella are cultivated commercially in large outdoor ponds and are harvested to produce dry algal meals, such as polyunsaturated fatty acids and oils for the health food industry, and coloring agents for the food and cosmetic industries. During the past decade, the advances in molecular biology and biochemistry of microalgae, along with the advances in biotechnology of microalgal mass cultivation, enabled this microalga to become a staple of commercial exploitation. In particular, the advent of molecular biology and mutagenesis inDunaliella has permitted enhancements in the carotenoids content of this green alga, making it more attractive for biotechnological applications. Accordingly, the present review summarizes the recent developments and advances in biotechnology of carotenoid production inDunaliella.     

An estimator for the proportional hazards model with multiple longitudinal covariates measured with error

In many longitudinal studies, it is of interest to characterize the relationship between a time-to-event (e.g. survival) and several time-dependent and time-independent covariates. Time-dependent covariates are generally observed intermittently and with error. For a single time-dependent covariate, a popular approach is to assume a joint longitudinal data-survival model, where the time-dependent covariate follows a linear mixed effects model and the hazard of failure depends on random effects and time-independent covariates via a proportional hazards relationship. Regression calibration and likelihood or Bayesian methods have been advocated for implementation; however, generalization to more than one time-dependent covariate may become prohibitive. For a single time-dependent covariate, Tsiatis and Davidian (2001) have proposed an approach that is easily implemented and does not require an assumption on the distribution of the random effects. This technique may be generalized to multiple, possibly correlated, time-dependent covariates, as we demonstrate. We illustrate the approach via simulation and by application to data from an HIV clinical trial.     

Photosystem-II repair and chloroplast recovery from irradiance stress: relationship between chronic photoinhibition,light-harvesting chlorophyll antenna size and photosynthetic productivity in Dunaliella salina (green algae)

High-light (HL) grown Dunaliella salina cells exhibit lower pigment content, a highly truncated chlorophyll (Chl) antenna size, and accumulation of photodamaged PS II centers in the chloroplast thylakoids (chronic photoinhibition). In HL-grown cells, the rate of photosynthesis saturated at higher irradiances and the quantum yield was lower compared to that of normally-pigmented low-light (LL) grown cells. In spite of these deficiencies, the light-saturated rate of photosynthesis for the HL-cells, when measured on a per chlorophyll basis, was 3 times greater than that of the LL-grown cells. To delineate the effect of photoinhibition from the Chl antenna size on quantum yield and rate of photosynthesis, HL-acclimated cells were switched to LL-conditions. Repair of photodamaged PS II, estimated from the recovery of functional PS II centers and from the increase in the quantum yield of photosynthesis, occurred with a half-time of 1 h. Chlorophyll accumulation in the cells occurred with a half-time of 4 h. The differential kinetics in repair versus Chl accumulation provided a window of opportunity, within about 2–3 h after the HLLL shift, when cells exhibited a high quantum yield of photosynthesis, a small Chl antenna size and a light-saturated rate that was 6–9 times greater than that of the normally pigmented LL-grown cells. The work provides insight on the temporal sequence of events at the chloroplast and thylakoid membrane levels, leading from a chronic photoinhibition of PS II to repair and recovery. It is suggested that it is possible to maximize photosynthetic productivity and light utilization in mass microalgal cultures by minimizing the light-harvesting Chl antenna size of the photosystems.     

13C shieldings, 18O isotope effects on 13C shieldings, and 57Fe-13C spin couplings of the Fe-C-O unit in superstructured hemoprotein models: Comparison with hemoproteins, C-O vibrational frequencies, and X-ray structural data

¹³C NMR spectra of several carbon monoxide (99.7% ¹³C and 11.8% ¹⁸O enriched) hemoprotein models with varying polar and steric effects of the distal organic superstructure and constraints of the proximal side are reported. This enables the ⁵⁷Fe-¹³C(O) coupling constants ( ), ¹³C shieldings ((¹³C)), and ¹⁸O isotope effects on¹³ C shieldings (¹¹³C(¹⁸O/¹⁶O)) to be measured and hence comparisons with hemoproteins, C-O vibrational frequencies and X-ray structural data to be made. Negative polar interactions in the binding pocket and inhibition of Fe//CO back-donation or positive distal polar interactions with amide NH groups appear to have little direct effect on couplings. Similarly, the axial hindered base 1,2-dimethylimidazole has a minor effect on the values despite higher rates of CO desorption being observed for such complexes. On the contrary,¹³ C shieldings vary widely and an excellent correlation was found between the infrared C-O vibrational frequencies ((C-O)) and¹³ C shieldings and a reasonable correlation with¹⁸ O isotope effects on ¹³C shieldings. This suggests that (¹³C), (C-O) and^{1 13} C(¹⁸O/¹⁶O) are accurate monitors of the multiple mechanisms by which steric and electronic interactions are released in superstructured heme model compounds. The ¹³C shieldings of heme models cover a 4.0 ppm range which is extended to 7.0 ppm when several HbCO and MbCO species at different pH values are included. The latter were found to obey a similar linear (¹³ (¹³C) versus (C-O) relationship, which proves that both heme models and heme proteins are homogeneous from the structural and electronic viewpoint. Our results suggest that (C-O), (¹³C) and ¹¹³C(¹⁸O/¹⁶O) measurements reflect similar interaction which is primarily the modulation of back-bonding from the Fe d to the CO * orbital by the distal pocket polar interactions. The lack of correlation between^{1 13} C(¹⁸O/¹⁶O) and crystallographic CO bond lengths (r(C-O)) reflects significant uncertainties in the X-ray determination of the carbon and oxygen positions.     

Dunaliella salina (Chlorophyta) with small chlorophyll antenna sizes exhibit higher photosynthetic productivities and photon use efficiencies than normally pigmented cells

The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light (LL: 100 μmol photon m^-2 s^-1) or high-light (HL: 2000 μmol photon m^-2 s^-1) conditions. Under LL, cells were normally pigmented (deep green) containing ∼500 chlorophyll (Chl) molecules per photosystem II (PSII) unit and ∼250 Chl molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chl per PSII and 100 Chl per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at ∼200 μmol photon m^-2 s^-1 with a rate (P_max) of ∼100 mmol O₂ (mol Chl)^-1 s^-1. In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. ∼2500 μmol photon m^-2 s^-1, and exhibited a three-fold higher P_max (∼300 mmol O₂ (mol Chl)^-1 s^-1) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting Chl antenna size increase, enhanced P_max to ∼675 mmol O₂ (mol Chl)^-1 s^-1. Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chl antenna size could exhibit 2–3 times higher productivities than currently achieved with normally pigmented cells. This revised version was published online in August 2006 with corrections to the Cover Date.