Dark Interval Research Articles

Short light–dark cycles affect sleep in mice

Environmental light has a strong impact on human physiology and behaviour, including cognitive functioning and alertness. Previous studies have shown that short light-dark (LD) cycles influence sleep in the albino rat. Rapid eye movement (REM) sleep increases after the onset of darkness and increases after light onset. In the present study, we investigated whether light affects sleep in mice. To this purpose the electroencephalogram and electromyogram of nine adult male C57BL/6 mice was recorded under 12 : 12 h baseline LD conditions, followed by 24 h continuous darkness (DD) and 6 days with LD cycles of different durations (2 h, 30 min, 14 min, 10 min, 4 min and 2 min), presented in a randomized order. NREM sleep was evenly distributed over the light and dark intervals of all short LD cycles. REM sleep, however, was increased during the dark intervals of short (10-30 min) LD cycles. Analysis showed that in these LD cycles, the increment in REM sleep was maximal in the second minute after dark onset, where the percentage of epochs with REM sleep increased significantly to 175% of baseline values. This increase was attributable to an increase in REM sleep episode duration. The recorded responses show that sleep in mice is affected by photic stimulation. The results demonstrate that pigmented animals can show REM sleep induction after dark onset and indicate that light has significant effects on the regulation of sleep.

Fractionated aminolevulinic acid–photodynamic therapy provides additional evidence for the use of PDT for non‐melanoma skin cancer

Photodynamic therapy (PDT) is an accepted treatment for superficial basal cel carcinoma (sBCC) and Bowens disease. In Rotterdam, extensive preclinical research has lead to an optimized twofold illumination scheme for aminolevulinic acid-PDT (ALA-PDT). To provide additional evidence of ALA-PDT for sBCC, Bowens disease (BD), nodular BCC (nBCC) and actinic keratosis (AK) using a 2-fold illumination scheme after a single application of ALA. Five hundred fifty-two lesions (430 sBCC, 20 nBCC, 32 BD, 70 AK) were treated with ALA-PDT using a twofold illumination scheme. ALA was applied topically for 4 h. Lesions were treated with two light fractions of 20 and 80 J/cm(2) separated by a 2-h dark interval. After a minimum follow-up of 12 months, in average follow-up of 2 years, an overall complete response of 95% was seen for all lesions. For sBCC, the complete response at 2 years was 97% (for AK 98%, for BD 84% and for nBCC 80% after 2 years). A sub-analysis of the results of lesions larger than 2 cm showed CR at 2 years of 89% for all lesions (n = 57). Cosmetic outcome was good to excellent in 95% of the treated lesions. ALA-PDT using a twofold illumination scheme of 20 plus 80 J/cm(2) separated by a 2-h dark interval leads to high complete response rates at 2 years and can be regarded as an evidence-based treatment modality for superficial growing non-melanoma skin cancer and the (pre)malignant AK. The Rotterdam fractionated approach should be included in future guidelines.

Circadian Response Reduction in Light and Response Restoration in Darkness: A “Skeleton” Light Pulse PRC Study in Mice (Mus musculus)

Entrainment may involve responses to dawn, to dusk, and to the light in between these transitions. Previous studies showed that the circadian system responds to only 2 light pulses, one at the beginning and one at the end of the day, in a similar way as to a full photoperiod, as long as the photoperiod is less than approximately 1/2 tau. The authors used a double 1-h light pulse protocol with different intervals of darkness in between (1, 2, 4, 7, 10, and 16 h) to study the phase responses of mice. The phase response curves obtained were compared to full light pulse PRCs of corresponding durations. Up to 6 hours, phase responses induced by double light pulses are virtually the same as by a corresponding full light pulse. The authors made a simple phase-only model to estimate the response reduction due to light exposure and response restoration due to dark exposure of the system. In this model, they assumed a 100% contribution of the first 1-h light pulse and fitted the reduction factor for the second light pulse to yield the best fit to the observations. The results suggest that after 1 h of light followed by less than 4 h of darkness, there is a considerable reduction in response to the second light pulse. Full response restoration requires more than 10 h of darkness. To investigate the influence of the duration of light on the response saturation, the authors performed a second series of experiments where the duration of the 2 light pulses was varied from 4 to 60 min each with a fixed duration of the stimulus (4 h). The response to 2 light pulses saturates when they are between 30 and 60 min long. In conclusion, double pulses replace single full light pulses of a corresponding duration of up to 6 h due to a response reduction during light, combined with response restoration during darkness. By the combined response reduction and response restoration, mice can maintain stable entrainment to the external LD cycle without being continuously exposed to it.

Light grating storage in cold atoms

We report the storage of a spatial light grating in a sample of cold caesium atoms. The grating is stored in the atomic medium using a backward four-wave-mixing laser beam configuration with two counterpropagating control fields and a noncollinear probe field. The grating was stored during a controllable dark interval after which turning on the control fields alone resulted in a light pulse emission in the forward and backward probe beam directions. Grating storage times up to 4 µs were observed.

Pigeons’ memory for sequences of light flashes when gap duration is an unreliable discriminative cue

In Experiment 1, pigeons were trained with a 1-sec dark and a 1-sec houselight-illuminated delay interval to discriminate between sequences of two and four flashes of light (feeder illumination). The sequences could be discriminated on the basis of the number of flashes, the number of gaps, or the duration of the gap between flashes. A choose-few bias was obtained at extended dark delays, but not at extended illuminated delays. Pigeons appeared to confuse long dark delays with the longer gap between flashes on few-sample trials. In Experiment 2, additional sample sequences were included that made gap duration an unreliable cue for discriminating between the few and many samples. A significant choose-many bias was obtained at extended dark delay intervals, but no biased forgetting was found at extended illuminated delays. The pigeons appeared to discriminate light flash sequences by relying on multiple temporal features of a sequence rather than using an event switch to count flashes. The biased-forgetting effects observed appear to be due to instructional ambiguity that results from the similarity of the delay interval to features of the flash sequences.

Dose and Timing of the First Light Fraction in Two-fold Illumination Schemes for Topical ALA-mediated Photodynamic Therapy of Hairless Mouse Skin¶

A fractionated illumination scheme in which a cumulative fluence of 100 J cm−2 is delivered in two equal light fractions separated by a dark interval of 2 h has been shown to considerably increase the efficacy of 5-aminolevulinic acid (ALA)–photodynamic therapy (PDT). The efficacy of such a scheme is further increased if the fluence of the first light fraction is reduced to 5 J cm−2. We have investigated the relationship between the PDT response and the kinetics of protoporphyrin IX (PpIX) fluorescence in the SKH1 HR hairless mouse for first fraction fluences below 5 J cm−2 delivered 4 h after the application of ALA and 10 J cm−2 delivered 2 h after the application of ALA. Illumination is performed using 514 nm at a fluence rate of 50 mW cm−2. Reducing the fluence of the first fraction to 2.5 J cm−2 does not result in significantly different visual skin damage. The PDT response, however, is significantly reduced if the fluence is lowered to 1 J cm−2, but this illumination scheme (1 + 99 J cm−2) remains significantly more effective than a single illumination of 100 J cm−2. A first light fraction of 10 J cm−2 can be delivered 2 h earlier, 2 h after the application of ALA, without significant reduction in the PDT response compared with 5 + 95 J cm−2 delivered 4 and 6 h after the application of ALA. The kinetics of PpIX fluorescence are consistent with those reported previously by us and do not explain the significant increase in PDT response with a two-fold illumination scheme. Histological sections of the illuminated volume showed a trend toward increasing extent and depth of necrosis for the two-fold illumination scheme in which the first light fraction is 5 J cm−2, compared with a single illumination scheme.

Partial Storage and Retrieval of a Light Pulse in a Cs Atomic Vapor with $\Lambda$-Type EIT

We are able to store and retrieve part of a Gaussian light pulse in Cs atomic vapors with a Λ-type electromagnetically induced transparency (EIT) scheme. After storing part of the probe light pulse by switching off a controlling field while the probe pulse was propagating through the vapor cell, we were able to retrieve the pulse when the controlling field was turned on after some dark interval. By changing the coupling off time by a constant quantity, we were able to reproduce the whole pulse shape, and by changing the dark interval, we were able to measure the decay time of atomic coherence, which is the timekeeper of information.

Single-photon-state generation from a continuous-wave nondegenerate optical parametric oscillator

We present a theoretical treatment of conditional preparation of one-photon states from a continuous-wave nondegenerate optical parametric oscillator. We obtain an analytical expression for the output state Wigner function, and we maximize the one-photon state fidelity by varying the temporal mode function of the output state. We show that a higher production rate of high fidelity Fock states is obtained if we condition the outcome on dark intervals around trigger photo detection events.

Flash-Induced Blocking of the High-Affinity Manganese-Binding Site in Photosystem II by Iron Cations: Dependence on the Dark Interval between Flashes and Binary Oscillations of Fluorescence Yield

Incubation of Fe(II) cations with Mn-depleted PSII membranes (PSII(-Mn)) under weak continuous light is accompanied by blocking of the high-affinity, Mn-binding (HAZ) site with ferric cations (Semin, B.K. et al. Biochemistry 2002, 41, 5854-5864). In this study we investigated the blocking yield under single-turnover flash conditions. The flash-probe fluorescence method was used to estimate the blocking efficiency. We found that the yield of blocking increases with flash number and reaches 50% after 7 flashes. When the dark interval between the flashes (Delta t) was varied, we found that the percentage of blocking decreases at Delta t < 100 ms (t 1/2, 4-10 ms). No inhibition of the blocking yield was found at longer time intervals (as with photoactivation). This result shows the necessity of a dark rearrangement during the blocking process (the dual-site hypothesis described in the text) and indicates the formation of a binuclear iron center. During the blocking experiments, we found a binary oscillation of the Fmax elicited during a train of flashes. The oscillations were observed only in the presence of Fe(II) cations or other electron donors (including Mn(II)) but not in the presence of Ca2+. Chelators had no effect on the oscillations. Our results indicate that the oscillations are due to processes on the acceptor side of PSII and to the appearance of "acceptor X" after odd flashes. Acceptor X is reduced by QA- at very high rate (<<2 ms), is not sensitive to DCMU, and is rather stable in the dark (t l/2 approximately 2 min). These properties are similar to those of nonheme Fe(III) (Fe(III)NHI). When Fe(II)NHI was oxidized with ferricyanide (Fe(CN)6), the fluorescence decay kinetics and yield of fluorescence were identical to those observed when the sample was exposed to 1 flash prior to the fluorescence measurement. We suggest that acceptor X is Fe(III)NHI, oxidized by the semiquinone form of QB-. This is similar to the mechanism of "reduction-induced oxidation of Fe(II)NHI" by exogenous quinones reported in the literature. We suggest that involvement of QB- in the oxidation of Fe(II)NHI in PSII(-Mn) membranes is due to the modification of the QB-binding site and increase of its redox potential resulting from extraction of the functional Mn cluster.

Fractionated illumination after topical application of 5-aminolevulinic acid on normal skin of hairless mice: The influence of the dark interval

We have previously shown that light fractionation during topical aminolevulinic acid based photodynamic therapy (ALA-PDT) with a dark interval of 2 h leads to a significant increase in efficacy in both pre-clinical and clinical PDT. However this fractionated illumination scheme required an extended overall treatment time. Therefore we investigated the relationship between the dark interval and PDT response with the aim of reducing the overall treatment time without reducing the efficacy. Five groups of mice were treated with ALA-PDT using a single light fraction or the two-fold illumination scheme with a dark interval of 30 min, 1, 1.5 and 2 h. Protoporphyrin IX fluorescence kinetics were monitored during illumination. Visual skin response was monitored in the first seven days after PDT and assessed as PDT response. The PDT response decreases with decreasing length of the dark interval. Only the dark interval of 2 h showed significantly more damage compared to all the other dark intervals investigated ( P < 0.05 compared to 1.5 h and P < 0.01 compared to 1 h, 30 min and a single illumination). No relationship could be shown between the utilized PpIX fluorescence during the two-fold illumination and the PDT response. The rate of photobleaching was comparable for the first and the second light fraction and not dependent of the length of dark interval used. We conclude that in the skin of the hairless mouse the dark interval cannot be reduced below 2 h without a significant reduction in PDT efficacy.

Evidence for a bystander role of neutrophils in the response to systemic 5‐aminolevulinic acid‐based photodynamic therapy

A significant increase in the number of circulating and tumour neutrophils immediately after therapy was observed while investigating the increase in response of tissues to aminolevulinic acid-based photodynamic therapy (ALA-PDT) using a twofold illumination scheme with a prolonged dark interval. The action of (tumour) neutrophils is an important therapeutic adjunct to the deposition of singlet oxygen within the treatment volume, for many photosensitizers. It is not known if those phagocytes contribute to the improved outcome of ALA-PDT. In this study we investigated the role of neutrophils in the response to PDT using systemic ALA with and without light fractionation. Rhabdomyosarcoma, transplanted in the thigh of female WAG/Rij rats were illuminated transdermally using 633 nm light following i.v. administration of 200 mg/kg ALA. The pharmacokinetics of protoporphyrin IX (PpIX) within the tumour tissue during therapy were determined to compare with that observed in other models for topical administration of ALA. PDT was performed under immunologically normal or neutropenic conditions using various illumination schemes. The number of neutrophils in tumour and in the circulation were determined as a function of time after treatment and compared with growth delay of each scheme. Fluorescence spectroscopy revealed similar pharmacokinetics of PpIX to those observed during and after topical ALA-PDT. The number of neutrophils within the illuminated tumour and in the circulation increased significantly following therapy. This increase in the number of neutrophils was associated with an increase in the efficacy of therapy: the more effective the therapy the greater the increase in tumour and blood neutrophils. Administration of anti-granulocyte serum treatment prevented the influx of neutrophils after ALA-PDT, but did not lead to a significant decrease in the efficacy of the PDT treatment on the growth of the tumour for any illumination scheme investigated. These results indicate that the magnitude of damage inflicted on the tumour by ALA-PDT does not depend on the presence of neutrophils in the tumour or circulation and that the role of neutrophils in ALA-PDT is much less important than in PDT using other photosensitizers. These data contribute to the understanding of the mechanism of response of tissue to systemic ALA-PDT.

Non-Poissonian intermittent fluorescence from complex structured environments

We characterize the photon-counting statistics of single-chromophore systems submitted to continuous laser radiation and embedded in a complex structured environment able to induce strong non-Markovian effects in the decay dynamics. In the weak-laser-excitation regime, the photon-emission process can be described through a delay function. We demonstrate that the dynamics, by itself, is able to develop a non-Poissonian intermittent fluorescence phenomenon where the bright and dark intervals are characterized by probability distributions that may depart from an exponential one.

A placebo-controlled randomized study on the clinical effectiveness, immunohistochemical changes and protoporphyrin IX accumulation in fractionated 5-aminolaevulinic acid-photodynamic therapy in patients with psoriasis

Topical 5-aminolaevulinic acid (ALA)-photodynamic therapy (PDT) for the treatment of psoriasis has been evaluated in a few studies. In these studies different treatment parameters were used, there was a variable clinical response, and a nonhomogeneous fluorescence was seen after irradiation with Wood's light. To study the clinical effectiveness, immunohistochemical changes and protoporphyrin IX accumulation in ALA-PDT in patients with psoriasis. Eight patients with stable plaque psoriasis with symmetrical involvement were included in the study. Two symmetrical plaques were randomly allocated to PDT either with 10% ALA or with placebo. Irradiation consisted of 2 and 8 J cm(-2) with a dark interval of 2 h (Waldmann PDT 1200 L, 600-750 nm, 40 mW cm(-2)) once weekly for 4 weeks. Before, during and after irradiation, fluorescence diagnosis was performed. Biopsies were taken at baseline, week 1 and week 6 for immunohistochemical assessment. Psoriatic plaques were clinically assessed using the plaque severity (sum) score. Fluorescence diagnosis was performed and expression of immunohistochemical markers for proliferation, differentiation and T-cell infiltration [Ki67, keratin 10 (K10), CD4, CD8 and CD45RO] was assessed. From week 1 up to week 6, ALA-PDT gave a significant reduction in the number of Ki67+ nuclei, while the K10 expression increased. After 6 weeks significant improvement was observed for CD8 and CD45RO. These changes were absent in the placebo-treated lesions. The sum scores were also significantly lower in the ALA-treated plaques. Heterogeneity of macroscopic fluorescence was observed during treatment despite keratolytic treatment. The present study shows that clinical improvement during fractionated ALA-PDT in psoriasis parallels histological improvement as seen in normalization of epidermal proliferation, differentiation and infiltration of relevant T-cell subsets. Optimizing the current treatment protocol may increase clinical efficacy further.

Fruit Pungency of 'Shishito' Pepper as Affected by a Dark Interval in Continuous Fluorescent Illumination with Temperature Alteration

シシトウの閉鎖人工照明栽培における果実の辛味低減を目的とし, 暗期挿入および暗期低温の効果について検討した.通常の栽培では辛味を生じないシシトウ‘ししほまれ’を供試し, 植物体上部での光強度が15～350 μmolm-2s-1 になるように白色蛍光灯を用いて照明し, CO2濃度を800 ppmに制御した人工気象器内で栽培した. 明暗サイクルを連続照明および6時間暗期挿入, 暗期の温度を28, 20, 16℃とした. 明期の温度はいずれも28℃とした. 収穫果実の胎座組織からカプサイシンをメタノールで抽出し, 高速液体クロマトグラフにより測定した.食味試験の結果, 強い辛味が感じられなかった果実における胎座のカプサイシン濃度は, いずれも50 mg/100 gDW以下であった. 自然光･自然日長栽培株の果実は, 90%がその範囲内にあった.自然光+電照により24 時間日長とすると, 果実のカプサイシン濃度はやや上昇した. 人工気象器内で連続照明･28℃一定で栽培すると, カプサイシン濃度が著しく上昇し, 90%の果実が50 mg/100 gDW 以上であり, 60%の果実が500 mg/100 gDW 以上の高い値を示した. 6時間の暗期を挿入すると,カプサイシン濃度が減少し, 50 mg/100 gDW 以上の果実の割合が約60%, 500 mg/100 gDW の果実の割合が20% になった.さらに, 暗期の温度を16℃に下げると, カプサイシン濃度がさらに減少し, 50%以上の果実が50 mg/100 gDW 以下の値を示した. 果実当たり種子数とカプサイシン含量の関係を調べた結果, 両者には負の相関があり, 種子数が40個以上と多い果実はすべてカプサイシン含量が低かった. また, 温度が28℃一定の場合, カプサイシンの濃度が高く, 果実当たりの種子数が少なかった. これらのことから, 種子形成とカプサイシン生成との関係が示唆された.本研究の結果, 人工気象器内で連続光･28℃一定下でシシトウ果実に生じる強い辛味は, 暗期挿入と暗期低温で低減しうることが示された.

Effects of Dark Adaptation on Light-Induced Electron Transport through Photosystem I in the Cyanobacterium Synechocystis sp. PCC 6803

Kinetics of the redox reactions in the reaction center (P700) of photosystem I (PSI) of the cyanobacterium Synechocystis sp. PCC 6803 have been studied by EPR spectroscopy. The redox kinetics were recorded based on accumulation of the EPRI signal when the final signal was the sum of individual signals produced in response to illumination of the cells. After prolonged (more than 3 sec) dark intervals between illuminations, the kinetic curve of the EPR signal from P700+ was multiphasic. After a sharp increase in the signal amplitude at the beginning of illumination (phase I), the amplitude rapidly (for 0.1-0.2 sec) decreased (phase II). Then the signal amplitude gradually increased (phase III) until the steady rate of electron transfer was established. With short-term (1 sec) dark intervals between the flashes and also in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the kinetics of the light-induced increase in the EPR signal from P700+ were monophasic. Inhibition with iodoacetamide of electron transport on the acceptor side of PSI under anaerobic conditions or an increase in the amount of respiration substrates on addition of glucose into a suspension of DCMU-treated wild-type cells increased the level of P700 reduction in phase III. The findings suggest that the kinetic curve of the EPR signal from P700+ is determined by both the electron entrance onto P700+ on the donor side of PSI and activity of electron acceptors of PSI.

Hypericin‐mediated Photocytotoxic Effect on HT‐29 Adenocarcinoma Cells Is Reduced by Light Fractionation with Longer Dark Pause Between Two Unequal Light Doses

The present study demonstrates the in vitro effect of hypericin-mediated PDT with fractionated light delivery. Cells were photosensitized with unequal light fractions separated by dark intervals (1 or 6 h). We compared the changes in viability, cell number, survival, apoptosis and cell cycle on HT-29 cells irradiated with a single light dose (12 J/cm(2)) to the fractionated light delivery (1 + 11 J/cm(2)) 24 and 48 h after photodynamic treatment. We found that a fractionated light regime with a longer dark period resulted in a decrease of hypericin cytotoxicity. Both cell number and survival were higher after light sensitization with a 6-h dark interval. DNA fragmentation occurred after a single light-dose application, but in contrast no apoptotic DNA formation was detected with a 6-h dark pause. After fractionation the percentage of cells in the G1 phase of the cell cycle was increased, while the proportion of cells in the G2 phase decreased as compared to a single light-dose application, i.e. both percentage of cells in the G1 and G2 phase of the cell cycle were near control levels. We presume that the longer dark interval after the irradiation of cells by first light dose makes them resistant to the effect of the second illumination. These findings confirm that the light application scheme together with other photodynamic protocol components is crucial for the photocytotoxicity of hypericin.

Enhancing the photodynamic effect of hypericin in tumour spheroids by fractionated light delivery in combination with hyperoxygenation

The aim of this study was to explore the hypothesis of oxygen depletion during light irradiation as a possible explanation for the incomplete response seen after hypericin-mediated photodynamic therapy (PDT) under specific conditions. To investigate this, we performed PDT experiments using transitional cell carcinoma spheroids with fractionated light irradiation and hyperoxygenation. After 2-h incubation with 3 different hypericin concentrations, spheroids were irradiated either continuously or with fractionated light delivery. The effect of hyperoxygenation was investigated by bubbling normobaric oxygen in the solution surrounding the spheroids before continuous irradiation or during the dark interval of light fractionation. The PDT efficacy was evaluated with an MTT antiproliferation assay and apoptotic cells were visualized after PDT by DAPI staining. Our results show that fractionated light delivery with dark intervals ranging from 1 to 10 min does not enhance the PDT efficacy in spheroids at all, whereas hyperoxygenation, using appropriate hypericin concentrations and oxygenation intervals, results in a virtually complete malignant cell killing through apoptosis. This study suggests that oxygen depletion is the major source of relative treatment failure in hypericin-mediated PDT with spheroids, which can only be overcome with hyperoxygenation. Therefore, whole bladder wall PDT with hypericin is likely to become a very efficient antitumoural treatment against superficial bladder cancer, on the condition that instillation fluids are hyperoxygenated during light irradiation.

Stimulation of Ca2+ uptake into micropropagated potato plantlets by UV light and vitamin D3

Micropropagated potato plantlets (Solanum tuberosum cvs Acadia Russet, Red Gold, Red Pontiac, and Russet Burbank) were used to test the effects of exposure to ultra violet rays (UV) or inclusion of vitamin D3 (cholecalciferol) in the test solution on plantlet calcium (Ca) uptake. Ca uptake was determined by measuring shoot tissue45Ca2+ concentration inex vitro plantlets placed into test solutions containing radiolabelled calcium (45CaCl2). Shoot tissue45Ca2+ concentration was very significantly increased in all cultivars exposed for 24 h to UV treatment compared with control plantlets. This increase in shoot45Ca2+ concentration was similar (three cultivars) or greater (one cultivar) than that caused by 10 ing L−1 vitamin D1 in the test solution. When plantlets were exposed to UV, then placed for 24 h in the dark, significantly greater shoot45Ca2+ concentrations occurred compared with plantlets tested immediately following treatment. This suggests that a change in the UV-elicited cellular product occurred during the dark interval that promoted more Ca uptake into plantlets.

Performance Analysis of AC-Coupled Burst-Mode Receiver for Fiber-Optic Burst Switching Networks

A generalized theoretical analysis of an AC-coupled fiber-optic burst-mode receiver is presented. This receiver is designed to operate in optical burst-switching networks using DC-balanced data coding such as 8B10B. Analytic expressions for the recovery time are derived as a function of the system dynamic range, power penalty, and data coding format. The theoretical calculations are verified with a detailed simulation. It is shown that locking time of the order of nanoseconds can be achieved with commercially available AC-coupled receivers. The burst-mode receiver can adapt to large (>10 dB) amplitude variations in 30 ns with a power penalty of 2 dB at 12.5 Gb/s. An overall optimization of the transmitter-receiver link-setup time is performed for an optical burst-switching network based on tunable laser transmitters. The dark interval during laser tuning (/spl sim/50 ns) is shown to have a beneficial impact on the receiver's response time, effectively reducing its locking time to a few nanoseconds, thus resulting in an overall link setup time of about 50 ns, limited by the laser's tuning time.

Carbon mass balance methodology to characterize the growth of pigmented marine bacteria under conditions of light cycling

A carbon mass balance methodology employing minimal measurements was applied to heterotrophic and photoheterotrophic marine bacteria grown under constant dilution and exposed to 12-h intervals of light or darkness. Carbon mass balance calculations using measurements taken every 3 h closed to within 93-103% using dissolved organic carbon, biomass carbon and CO2 production data only, indicating that background interference from dissolved inorganic carbon variations in the amended seawater medium was not significant. Neither strain was observed to sustain a net CO2 fixation using paramagnetic measurement of oxygen uptake rates (OUR), indicating a need for more sensitive on-line measurement techniques for OUR. Photoheterotrophic growth demonstrated lower carbon-mole biomass yields (0.41+/-0.026 vs. 0.64+/-0.013 mol mol(-1)) despite higher specific glucose uptake rates (0.025 vs. 0.02 mol mol(-1) h(-1)), suggesting that bioreactor-based study of marine bacteria can present growth modes that are different from those encountered in the marine environment.