173 research outputs found
Responses of a Locust Looming Sensitive Neuron, Flight Muscle Activity and Body Orientation to Changes in Object Trajectory, Background Complexity, and Flight Condition
Survival is one of the highest priorities of any animal. Interaction in the environment with
conspecifics, predators, or objects, is driven by evolution of systems that can efficiently and
rapidly respond to potential collision with these stimuli. Flight introduces further complexity for
a collision avoidance system, requiring an animal to compute air speed, wind speed, ground
speed, as well as transverse and longitudinal image flow, all within the context of detecting an
approaching object. Understanding the mechanisms underlying neural control and coordination
of motor systems to produce behaviours in response to the natural environment is a main goal of
neuroethology. Locusts have a tractable nervous system, and a robust, reproducible collision
avoidance response to looming stimuli. This tractable system allows recording from the nerve
cord and flight muscles with precision and reliability, allowing us to answer important questions
regarding the neuronal control of muscle coordination and, in turn, collision avoidance behaviour
during flight. In flight, a collision avoidance behaviour will most often be a turn away from the
approaching stimulus. I tested the hypothesis that during loosely tethered flight, synchrony
between flight muscles increases just prior to the initiation of a turn and that muscle
synchronization would correlate with body orientation changes during flight steering. I found
that hind and forewing flight muscle synchronization events correlated strongly with forewing
flight muscle latency changes, and to pitch and roll body orientation changes in response to a
lateral looming visual stimulus. These findings led me to investigate further the role of the
looming-sensitive descending contralateral movement detector (DCMD) neuron in flight muscle
coordination and the initiation of forewing asymmetry in rigidly tethered locusts that generate a
flight-like rhythm. By conducting simultaneous recordings from the nerve cord, forewing flight
muscles, and visually recording the wing positions within the same flying animal, I hypothesized
that DCMD burst properties would correlate with flight muscle activity changes and the
initiation of wing asymmetry associated with turning behaviour. Furthermore, I accessed the
effect of manipulating background complexity of the locust’s visual environment, looming object
trajectory, and the putative effect of mechanosensory feedback during flight, on DCMD burst
firing rate properties. DCMD burst properties were affected by changes in background
complexity and object trajectory, and most interestingly during flight. This suggests that
reafferent feedback from the flight motor system modulates the DCMD signal, and therefore
represents a more naturalistic representation of collision avoidance behaviour. A pivotal
discovery in my study was the temporal role of bursting in collision avoidance behaviour. I
found that the first burst in a DCMD spike train represents the earliest detectable neuronal event
correlated with muscle activity changes and the creation of wing asymmetry. I found strong
correlations across all object trajectories and background complexities, between the timing of the
first bursts, flight muscle activity changes and the initiation of wing asymmetry. These findings
reinforce the importance of the temporal properties of DCMD bursting in collision avoidance
behaviour
Buildup of Magnetic Shear and Free Energy During Flux Emergence and Cancellation
We examine a simulation of flux emergence and cancellation, which shows a
complex sequence of processes that accumulate free magnetic energy in the solar
corona essential for the eruptive events such as coronal mass ejections (CMEs),
filament eruptions and flares. The flow velocity at the surface and in the
corona shows a consistent shearing pattern along the polarity inversion line
(PIL), which together with the rotation of the magnetic polarities, builds up
the magnetic shear. Tether-cutting reconnection above the PIL then produces
longer sheared magnetic field lines that extend higher into the corona, where a
sigmoidal structure forms. Most significantly, reconnection and upward
energy-flux transfer are found to occur even as magnetic flux is submerging and
appears to cancel at the photosphere. A comparison of the simulated coronal
field with the corresponding coronal potential field graphically shows the
development of nonpotential fields during the emergence of the magnetic flux
and formation of sunspots
Simulation of Flux Emergence from the Convection Zone to the Corona
Here, we present numerical simulations of magnetic flux buoyantly rising from
a granular convection zone into the low corona. We study the complex
interaction of the magnetic field with the turbulent plasma. The model includes
the radiative loss terms, non-ideal equations of state, and empirical corona
heating. We find that the convection plays a crucial role in shaping the
morphology and evolution of the emerging structure. The emergence of magnetic
fields can disrupt the convection pattern as the field strength increases, and
form an ephemeral region-like structure, while weak magnetic flux emerges and
quickly becomes concentrated in the intergranular lanes, i.e. downflow regions.
As the flux rises, a coherent shear pattern in the low corona is observed in
the simulation. In the photosphere, both magnetic shearing and velocity
shearing occur at a very sharp polarity inversion line (PIL). In a case of
U-loop magnetic field structure, the field above the surface is highly sheared
while below it is relaxed
Dynamic Coupling of Convective Flows and Magnetic Field during Flux Emergence
We simulate the buoyant rise of a magnetic flux rope from the solar
convection zone into the corona to better understand the energetic coupling of
the solar interior to the corona. The magnetohydrodynamic model addresses the
physics of radiative cooling, coronal heating and ionization, which allow us to
produce a more realistic model of the solar atmosphere. The simulation
illustrates the process by which magnetic flux emerges at the photosphere and
coalesces to form two large concentrations of opposite polarities. We find that
the large-scale convective motion in the convection zone is critical to form
and maintain sunspots, while the horizontal converging flows in the near
surface layer prevent the concentrated polarities from separating. The foot
points of the sunspots in the convection zone exhibit a coherent rotation
motion, resulting in the increasing helicity of the coronal field. Here, the
local configuration of the convection causes the convergence of opposite
polarities of magnetic flux with a shearing flow along the polarity inversion
line. During the rising of the flux rope, the magnetic energy is first injected
through the photosphere by the emergence, followed by energy transport by
horizontal flows, after which the energy is subducted back to the convection
zone by the submerging flows
Representations of Time Coordinates in FITS
In a series of three previous papers, formulation and specifics of the
representation of World Coordinate Transformations in FITS data have been
presented. This fourth paper deals with encoding time. Time on all scales and
precisions known in astronomical datasets is to be described in an unambiguous,
complete, and self-consistent manner. Employing the well--established World
Coordinate System (WCS) framework, and maintaining compatibility with the FITS
conventions that are currently in use to specify time, the standard is extended
to describe rigorously the time coordinate. World coordinate functions are
defined for temporal axes sampled linearly and as specified by a lookup table.
The resulting standard is consistent with the existing FITS WCS standards and
specifies a metadata set that achieves the aims enunciated above.Comment: FITS WCS Paper IV: Time. 27 pages, 11 table
HIV-1 gp120 Mannoses Induce Immunosuppressive Responses from Dendritic Cells
The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is a vaccine immunogen that can signal via several cell surface receptors. To investigate whether receptor biology could influence immune responses to gp120, we studied its interaction with human, monocyte-derived dendritic cells (MDDCs) in vitro. Gp120 from the HIV-1 strain JR-FL induced IL-10 expression in MDDCs from 62% of donors, via a mannose C-type lectin receptor(s) (MCLR). Gp120 from the strain LAI was also an IL-10 inducer, but gp120 from the strain KNH1144 was not. The mannose-binding protein cyanovirin-N, the 2G12 mAb to a mannose-dependent gp120 epitope, and MCLR-specific mAbs inhibited IL-10 expression, as did enzymatic removal of gp120 mannose moieties, whereas inhibitors of signaling via CD4, CCR5, or CXCR4 were ineffective. Gp120-stimulated IL-10 production correlated with DC-SIGN expression on the cells, and involved the ERK signaling pathway. Gp120-treated MDDCs also responded poorly to maturation stimuli by up-regulating activation markers inefficiently and stimulating allogeneic T cell proliferation only weakly. These adverse reactions to gp120 were MCLR-dependent but independent of IL-10 production. Since such mechanisms might suppress immune responses to Env-containing vaccines, demannosylation may be a way to improve the immunogenicity of gp120 or gp140 proteins
Live Attenuated B. pertussis as a Single-Dose Nasal Vaccine against Whooping Cough
Pertussis is still among the principal causes of death worldwide, and its incidence is increasing even in countries with high vaccine coverage. Although all age groups are susceptible, it is most severe in infants too young to be protected by currently available vaccines. To induce strong protective immunity in neonates, we have developed BPZE1, a live attenuated Bordetella pertussis strain to be given as a single-dose nasal vaccine in early life. BPZE1 was developed by the genetic inactivation or removal of three major toxins. In mice, BPZE1 was highly attenuated, yet able to colonize the respiratory tract and to induce strong protective immunity after a single nasal administration. Protection against B. pertussis was comparable to that induced by two injections of acellular vaccine (aPV) in adult mice, but was significantly better than two administrations of aPV in infant mice. Moreover, BPZE1 protected against Bordetella parapertussis infection, whereas aPV did not. BPZE1 is thus an attractive vaccine candidate to protect against whooping cough by nasal, needle-free administration early in life, possibly at birth
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