Control of Phytoplankton Production in a Shallow, Turbid Estuary.

Water column primary production and chlorophyll were sampled between 1986-1991 in Fourleague Bay, LA, a shallow (1.5 m), river-dominated estuary that is extremely turbid (K\sb{\rm D} = 4.44 m\sp{-1}). A high speed system for continuous flow-through sampling, Dataflow\sp\copyright, was developed to measure physicochemical variables and in vivo chlorophyll fluorescence at high temporal (1 s) and spatial (5 m) resolution from a small boat. Phytoplankton net primary production (NPP) was measured using an incubator which rotated bottles to prevent settling of the contents. NPP was found to be artificially increased by 10-83% at high light levels in non-rotated bottles when cells and sediments settled, reducing photoinhibition. Chlorophyll (17-27 $\mu$g L\sp{-1}) and NPP (0-4.5 g m\sp{-2} d\sp{-1}) distribution varied with season, and was correlated with K\sb{\rm D} and temperature, but not with nutrients. Spatially, chlorophyll was lower in the upper bay, increasing toward the middle estuary and laterally toward shores, especially in bayous, where concentrations were up to 42% higher than open bay waters. Bayous may tidally export chlorophyll to the bay. Turbidity from SPM (64 mg L\sp{-1}) was generated by river flow in spring and wind and current resuspension in summer and fall. Minimum water column NPP occurred in the upper estuary during spring, coincident with maximum turbidity. Annually, NPP averaged about 400 g C m\sp{-2}, peaking in fall in the upper estuary. Phytoplankton photosynthetic parameters were adapted to a high light regime: P\sp{\rm B}\sb{\rm max} averaged 10.99 $\mu$g C $\mu$g Chla\sp{-1} h\sp{-1}, I\sb{\rm K} ranged from 150-400 $\mu$E m\sp{-2} s\sp{-1}, and \alpha\sp{\rm B} averaged 0.05 $\mu$g C $\mu$g Chl a\sp{-1} h\sp{-1} $\mu$E m\sp{-2} s\sp{-1}. Frequent vertical circulation of phytoplankton in the shallow water column exposes them briefly to high light, sufficient to establish high photosynthetic capacity for the community, and prevent photoadaptation to lower light at depth. Parameters were not correlated with subsurface light, but integrated water column NPP was, indicating light control of NPP. In a simulation model, construction of a levee across the bay entrance had little impact on productivity, but shell dredging activity increased turbidity and reduced primary production nearly 50%, extinguishing the zooplankton population

Central Control of Brown Adipose Tissue Thermogenesis

Thermogenesis, the production of heat energy, is an essential component of the homeostatic repertoire to maintain body temperature during the challenge of low environmental temperature and plays a key role in elevating body temperature during the febrile response to infection. Mitochondrial oxidation in brown adipose tissue (BAT) is a significant source of neurally regulated metabolic heat production in many species from mouse to man. BAT thermogenesis is regulated by neural networks in the central nervous system which responds to feedforward afferent signals from cutaneous and core body thermoreceptors and to feedback signals from brain thermosensitive neurons to activate BAT sympathetic nerve activity. This review summarizes the research leading to a model of the feedforward reflex pathway through which environmental cold stimulates BAT thermogenesis and includes the influence on this thermoregulatory network of the pyrogenic mediator, prostaglandin E2, to increase body temperature during fever. The cold thermal afferent circuit from cutaneous thermal receptors, through second-order thermosensory neurons in the dorsal horn of the spinal cord ascends to activate neurons in the lateral parabrachial nucleus which drive GABAergic interneurons in the preoptic area (POA) to inhibit warm-sensitive, inhibitory output neurons of the POA. The resulting disinhibition of BAT thermogenesis-promoting neurons in the dorsomedial hypothalamus activates BAT sympathetic premotor neurons in the rostral ventromedial medulla, including the rostral raphe pallidus, which provide excitatory, and possibly disinhibitory, inputs to spinal sympathetic circuits to drive BAT thermogenesis. Other recently recognized central sites influencing BAT thermogenesis and energy expenditure are also described

Term small-for-gestational-age infants from low risk women are at significantly greater risk of adverse neonatal outcomes

Small-for-gestational age (SGA) infants (birthweight 37 weeks gestation). This is compounded by the fact that late pregnancy ultrasound is not the norm in many jurisdictions for this cohort of women. We thus investigated the relationship between birthweigh

On-chip multi-stage optical delay based on cascaded Brillouin light storage

Storing and delaying optical signals plays a crucial role in data centers, phased array antennas, communication, and future computing architectures. Here, we show a delay scheme based on cascaded Brillouin light storage that achieves multi-stage delay at arbitrary positions within a photonic integrated circuit. Importantly these multiple resonant transfers between the optical and acoustic domain are controlled solely via external optical control pulses, allowing cascading of the delay without the need of aligning multiple structural resonances along the optical circuit

Optimizing performance for on-chip SBS-based isolator

Non-reciprocal optical components such as isolators and circulators are crucial for preventing catastrophic back-reflection and controlling optical crosstalk in photonic systems. While non-reciprocal devices based on Brillouin intermodal transitions have been experimentally demonstrated in chip-scale platforms, harnessing such interactions has required a suspended waveguide structure, which is challenging to fabricate and is potentially less robust than a non-suspended structure, thereby limiting the design flexibility. In this paper, we numerically investigate the performance of a Brillouin-based isolation scheme in which a dual-pump-driven optoacoustic interaction is used to excite confined acoustic waves in a traditional ridge waveguide. We find that acoustic confinement, and therefore the amount of Brillouin-driven mode conversion, can be enhanced by selecting an appropriate optical mode pair and waveguide geometry of two arsenic based chalcogenide platforms. Further, we optimize the isolator design in its entirety, including the input couplers, mode filters, the Brillouin-active waveguide as well as the device fabrication tolerances. We predict such a device can achieve 30 dB isolation over a 38 nm bandwidth when 500 mW pump power is used; in the presence of a +/- 10 nm fabrication-induced width error, such isolation can be maintained over a 5-10 nm bandwidth

Photonic-chip-based tunable slow and fast light via stimulated Brillouin scattering

We report the first (to our knowledge) demonstration of photonic chip based tunable slow and fast light via stimulated Brillouin scattering. Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As2S3) rib waveguide with a group index change ranging from ∼−44 to +130, which results in a maximum delay of ∼23  ns at a relatively low gain of ∼23  dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array antenna, where integration and delays ∼10  ns are highly desirable

Photothermal colloid antibodies for shape-selective recognition and killing of microorganisms

We have developed a class of selective antimicrobial agents based on the recognition of the shape and size of the bacterial cells. These agents are anisotropic colloid particles fabricated as negative replicas of the target cells which involve templating of the cells with shells of inert material followed by their fragmentation. The cell shape recognition by such shell fragments is due to the increased area of surface contact between the cells and their matching shell fragments which resembles antibody-antigen interaction. We produced such "colloid antibodies" with photothermal mechanism for shape-selective killing of matching cells. This was achieved by the subsequent deposition of (i) gold nanoparticles (AuNPs) and (ii) silica shell over yeast cells, which were chosen as model pathogens. We demonstrated that fragments of these composite AuNP/silica shells act as "colloid antibodies" and can bind to yeast cells of the same shape and size and deliver AuNPs directly onto their surface. We showed that after laser irradiation, the localized heating around the AuNPs kills the microbial cells of matching shape. We confirmed the cell shape-specific killing by photothermal colloid antibodies in a mixture of two bacterial cultures of different cell shape and size. This approach opens a number of avenues for building powerful selective biocides based on combinations of colloid antibodies and cell-killing strategies which can be applied in new antibacterial therapies