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In addition to its motor functions, the cerebellum is involved in emotional regulation, anxiety and affect. We found that suppressing the firing of cerebellar Purkinje cells (PCs) rapidly excites forebrain areas that contribute to such functions (including the amygdala, basal forebrain and septum), but that the classic cerebellar outputs, the deep cerebellar nuclei, do not directly project there. We show that PCs directly inhibit parabrachial nuclei (PBN) neurons that project to numerous forebrain regions. Suppressing the PC–PBN pathway influences many regions in the forebrain and is aversive. Molecular profiling shows that PCs directly inhibit numerous types of PBN neurons that control diverse behaviors that are not involved in motor control. Therefore, the PC–PBN pathway allows the cerebellum to directly regulate activity in the forebrain, and may be an important substrate for cerebellar disorders arising from damage to the posterior vermis.

The cerebellum is thought to help detect and correct errors between intended and executed commands1,2and is critical for social behaviours, cognition and emotion3–6. Computations for motor control must be performed quickly to correct errors in real time and should be sensitive to small differences between patterns for fine error correction while being resilient to noise7. Influential theories of cerebellar information processing have largely assumed random network connectivity, which increases the encoding capacity of the network’s first layer8–13. However, maximizing encoding capacity reduces the resilience to noise7. To understand how neuronal circuits address this fundamental trade-off, we mapped the feedforward connectivity in the mouse cerebellar cortex using automated large-scale transmission electron microscopy and convolutional neural network-based image segmentation. We found that both the input and output layers of the circuit exhibit redundant and selective connectivity motifs, which contrast with prevailing models. Numerical simulations suggest that these redundant, non-random connectivity motifs increase the resilience to noise at a negligible cost to the overall encoding capacity. This work reveals how neuronal network structure can support a trade-off between encoding capacity and redundancy, unveiling principles of biological network architecture with implications for the design of artificial neural networks.

To understand how the cerebellar cortex transforms mossy fiber (MF) inputs into Purkinje cell (PC) outputs, it is vital to delineate the elements of this circuit. Candelabrum cells (CCs) are enigmatic interneurons of the cerebellar cortex that have been identified based on their morphology, but their electrophysiological properties, synaptic connections and function remain unknown. Here, we clarify these properties using electrophysiology, single-nucleus RNA sequencing, in situ hybridization and serial electron microscopy in mice. We find that CCs are the most abundant PC layer interneuron. They are GABAergic, molecularly distinct and present in all cerebellar lobules. Their high resistance renders CC firing highly sensitive to synaptic inputs. CCs are excited by MFs and granule cells and are strongly inhibited by PCs. CCs in turn primarily inhibit molecular layer interneurons, which leads to PC disinhibition. Thus, inputs, outputs and local signals converge onto CCs to allow them to assume a unique role in controlling cerebellar output.

The cerebellar cortex is a well-studied brain structure with diverse roles in motor learning, coordination, cognition and autonomic regulation. However,  a complete inventory of cerebellar cell types is currently lacking. Here, using recent advances in high-throughput transcriptional profiling1–3, we molecularly define cell types across individual lobules of the adult mouse cerebellum. Purkinje neurons showed considerable regional specialization, with the greatest diversity occurring in the posterior lobules. For several types of cerebellar interneuron, the molecular variation within each type was more continuous, rather than discrete. In particular, for the unipolar brush cells—an interneuron population previously subdivided into discrete populations—the continuous variation in gene expression was associated with a graded continuum of electrophysiological properties. Notably, we found that molecular layer interneurons were composed of two molecularly and functionally distinct types. Both types show a continuum of morphological variation through the thickness of the molecular layer, but electrophysiological recordings revealed marked differences between the two types in spontaneous firing, excitability and electrical coupling. Together, these findings provide a comprehensive cellular atlas of the cerebellar cortex, and outline a methodological and conceptual framework for the integration of molecular, morphological and physiological ontologies for defining brain cell types.

Climbing fibers from the inferior olive make strong excitatory synapses onto cerebellar Purkinje cell (PC) dendrites and trigger distinctive responses known as complex spikes. We found that, in awake mice, a complex spike in one PC suppressed conventional simple spikes in neighboring PCs for several milliseconds. This involved a new ephaptic coupling, in which an excitatory synapse generated large negative extracellular signals that nonsynaptically inhibited neighboring PCs. The distance dependence of complex spike–simple spike ephaptic signaling, combined with the known CF divergence, allowed a single inferior olive neuron to influence the output of the cerebellum by synchronously suppressing the firing of potentially over 100 PCs. Optogenetic studies in vivo and dynamic clamp studies in slice indicated that such brief PC suppression, as a result of either ephaptic signaling or other mechanisms, could effectively promote firing in neurons in the deep cerebellar nuclei with remarkable speed and precision.

Optical methods of interrogating neural circuits have emerged as powerful tools for understanding how the brain drives behaviors. Optogenetic proteins are widely used to control neuronal activity, while genetically encoded fluorescent reporters are used to monitor activity. These proteins are often expressed by injecting viruses, which frequently leads to inconsistent experiments due to misalignment of expression and optical components. Here, we describe how silk fibroin films simplify optogenetic experiments by providing targeted delivery of viruses. Films composed of silk fibroin and virus are applied to the surface of implantable optical components. After surgery, silk releases the virus to transduce nearby cells and provide localized expression around optical fibers and endoscopes. Silk films can also be used to express genetically encoded sensors in large cortical regions by using cranial windows coated with a silk/virus mixture. The ease of use and improved performance provided by silk make this a promising approach for optogenetic studies.

The calcium-sensing protein synaptotagmin 7 mediates facilitation that is masked by depression, but supports frequency-invariant transmission in mouse cerebellar and vestibular synapses.

Within the cerebellar cortex, mossy fibers (MFs) excite granule cells (GCs) that excite Purkinje cells (PCs), which provide outputs to the deep cerebellar nuclei (DCNs). It is well established that PC disruption produces motor deficits such as ataxia. This could arise from either decreases in ongoing PC-DCN inhibition, increases in the variability of PC firing, or disruption of the flow of MF-evoked signals. Remarkably, it is not known whether GCs are essential for normal motor function. Here we address this issue by selectively eliminating calcium channels that mediate transmission (CaV2.1, CaV2.2, and CaV2.3) in a combinatorial manner. We observe profound motor deficits but only when all CaV2 channels are eliminated. In these mice, the baseline rate and variability of PC firing are unaltered, and locomotion-dependent increases in PC firing are eliminated. We conclude that GCs are indispensable for normal motor performance and that disruption of MF-induced signals impairs motor performance.

The output of the cerebellar cortex is conveyed to the deep cerebellar nuclei (DCN) by Purkinje cells (PCs). Here, we characterize the properties of the PC-DCN synapse in juvenile and adult mice and find that prolonged high-frequency stimulation leads to steady-state responses that become increasingly frequency independent within the physiological firing range of PCs in older animals, resulting in a linear relationship between charge transfer and activation frequency. We used a low-affinity antagonist to show that GABAA-receptor saturation occurs at this synapse but does not underlie frequency-invariant transmission. We propose that PC-DCN synapses have two components of release: one prominent early in trains and another specialized to maintain transmission during prolonged activation. Short-term facilitation offsets partial vesicle depletion to produce frequency-independent transmission.

Explored the diversity and inclusion of our annual meeting. The authors compared our members’ diversity to the participation in the impactful portions of our annual conference as a measure of our organizational inclusion.

Aims. We observe the nearby, weakly-active single giant, Pollux, in order to directly study and infer the nature of its magnetic field.

Context. The young O-type star $\theta^1$Ori C, the brightest star of the Trapezium cluster in Orion, is one of only two known magnetic rotators among the O stars. However, not all spectroscopic variations of this star can be explained by the magnetic rotator model. We present results from a long-term monitoring to study these unexplained variations and to improve the stellar rotational period.

Aims. We study how chemical abundances of late B-, A-, and early F-type stars evolve with time, and we search for correlations between the abundance of chemical elements and other stellar parameters, such as effective temperature and ${\upsilon}\sin i$.

Context. Recent spectropolarimetric observations of Herbig Ae/Be stars have yielded new arguments in favour of a fossil origin for the magnetic fields of intermediate mass stars.

Context.The observed abundance peculiarities of many chemical species relative to the expected cluster metallicity in blue horizontal-branch (BHB) stars presumably appear as a result of atomic diffusion in the photosphere. The slow rotation (typically $v\sin{i}$< 10 km s-1) of BHB stars with effective temperatures Teff> 11 500 K supports this idea since the diffusion mechanism is only effective in a stable stellar atmosphere.

Aims.We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field.

Aims.We investigated a sample of 28 well-known spectroscopically-identified magnetic Ap/Bp stars, with weak, poorly-determined or previously undetected magnetic fields. The aim of this study is to explore the weak part of the magnetic field distribution of Ap/Bp stars.

Context.The evolution of magnetic fields in Ap stars during the main sequence phase is presently mostly unconstrained by observation because of the difficulty of assigning accurate ages to known field Ap stars.

Context.It is commonly believed that the observed overabundances of many chemical species relative to the expected cluster metallicity in blue horizontal branch (BHB) stars appear as a result of atomic diffusion in the photosphere. The slow rotation of BHB stars (with $T_{\rm eff} > 11\,500$K), typically $v\sin{i} < 10 $km s-1, is consistent with this idea.

We have obtained a time series of 81 high-cadence circular polarization observations of the rapidly oscillating Ap star HD 24712 with the new ESPaDOnS spectropolarimeter at CFHT. We used the high-S/N, high-resolution Stokes Iand Vspectra to investigate possible variation of the mean longitudinal field over the pulsation cycle in this roAp star. Our multiline magnetic field and radial velocity measurements utilized 143 spectral lines of rare-earth elements, attaining precision better than 13 G and 19 m s-1, respectively. A multiperiodic radial velocity variation with an amplitude of 40–136 m s-1is clearly detected at the known pulsation frequencies of HD 24712. At the same time, no evidence for pulsational changes of the magnetic field can be found. We derive a $3\sigma$upper limit of 10 G, or about 1% of the mean longitudinal field strength, for magnetic field oscillations in the upper atmosphere of HD 24712. The absence of detectable pulsational variability of the magnetic field provides a valuable constraint for the interaction between pulsations and magnetic field in roAp stars and is compatible with the recent predictions of detailed theoretical models of stellar magnetoacoustic oscillations.

Context.The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum.

Aims.This paper reports the photospheric, magnetic and circumstellar gas characteristics of the magnetic B8p star 36 Lyncis (HD 79158).

We report on the physical properties of the disk-like structure of B8 IIIp star 36 Lyncis from line syntheses of phase-resolved, high resolution spectra obtained from the International Ultraviolet Explorerarchives and from newly obtained ground-based spectra of the Hαabsorption profile. This disk is highly inclined to the rotational axis and betrays its existence every half rotation cycle as one of two opposing sectors pass in front of the star. Although the disk absorption spectrum is at least ten times too weak to be visible in optical iron lines during these occultations, its properties can be readily examined in a large number of UV “iron curtain” lines because of their higher opacities. The UV Fe II and Fe III lines in particular permit a determination of the disk temperature: $7500\pm500$K and a column density of $3_{-1.5}^{+3}\times10^{20}$cm-2. The analysis of the variations of the UV resonance lines brings out some interesting details about the radiative properties of the disks: (1) they are optically thick in the C IV and Si IV doublets, (2) the range of excitation of the UV resonance lines is larger at the primary occultation ($\phi = 0.00$) than at the secondary one, and (3) the relative strengths of the absorption peaks for the two occultations varies substantially from line to line. We have modeled the absorptions of the UV C IV resonance and Hαabsorptions by means of a simulated disk with opaque and translucent components. Our simulations suggest that a gap separates the star and the inner edge of the disk. The disk extends radially out to ≥10 $R_{*}$. The disk scale height perpendicular to the plane is ≈1 $R_{*}$. However, the sector causing the primary occultation is about four times thicker than the opposite sector. The C IV scattering region extends to a larger height than the Hαregion does, probably because it results from shock heating far from the cooler disk plane.

Context.About 5% of upper main sequence stars are permeated by a strong magnetic field, the origin of which is still matter of debate.

Aims.In this paper we confirm the presence of a globally-ordered, kG-strength magnetic field in the photosphere of the young O star $\theta^1$Orionis C, and examine the properties of its optical line profile variations.

Context.The chemically peculiar HgMn stars are a class of Bp stars which have historically been found to be both non-magnetic and non-variable. Remarkably, it has recently been demonstrated that the bright, well-studied HgMn star αAnd exhibits clear Hg iiline profile variations indicative of a non-uniform surface distribution of this element.

We report the discovery, using FORS1 at the ESO-VLT and ESPaDOnS at the CFHT, of magnetic fields in the young A-type stars HD 101412, V380 Ori and HD 72106A. Two of these stars (HD 101412 and V380 Ori) are pre-main sequence Herbig Ae/Be (HAeBe) stars, while one (HD 72106A) is physically associated with a HAeBe star. Remarkably, evidence of surface abundance spots is detected in the spectra of HD 72106A. The magnetic fields of these objects display intensities of order 1 kG at the photospheric level, are ordered on global scales, and appear in approximately 10% of the stars studied. Based on these properties, the detected stars may well represent pre-main sequence progenitors of the magnetic Ap/Bp stars. The low masses inferred for these objects (2.6, 2.8 and 2.4 $M_\odot$) represent additional contradictions to the hypothesis of Hubrig et al. (2000, ApJ, 539, 352), who claim that magnetic fields appear in intermediate-mass stars only after 30% of their main sequence evolution is complete. Finally, we fail to confirm claims by Hubrig et al. (2004, A&A, 428, L1) of magnetic fields in the Herbig Ae star HD 139614.

During a survey of field strengths in upper main sequence stars in open clusters, we observed the star NGC 2244-334 in the Rosette Nebula cluster and discovered an extraordinarily large mean longitudinal field of about -9 kG, the second largest longitudinal field known in a non-degenerate star. This star appears to be a typical Ap He-wk (Si) star of about $4~M_\odot$. Spectrum synthesis using a line synthesis code incorporating the effects of the strong magnetic field indicates that He is underabundant by about 1.5 dex, and C, O and Mg by about 0.1–0.4 dex, while Si, Mn and Fe are overabundant by about 1 dex, and Cr and Ti are nearly 2 dex overabundant.
Cluster membership for this star is secure, so its age is about $2\times 10^6$yr, which is less than 3% of its main sequence lifetime. This star is one of the very youngest magnetic upper main sequence stars with a well-determined age, and confirms that both magnetic fields and strong chemical peculiarity can appear in stars which are both extremely young and very close to the ZAMS.

We present the first investigation of the structure of the stellar surface magnetic field using line profiles in all four Stokes parameters. We extract the information about the magnetic field geometry and abundance distributions of the chemically peculiar star 53 Cam by modelling time-series of high-resolution spectropolarimetric observations with the help of a new magnetic Doppler imaging code. This combination of the unique four Stokes parameter data and state-of-the-art magnetic imaging technique makes it possible to infer the stellar magnetic field topology directly from the rotational variability of the Stokes spectra. In the magnetic imaging of 53 Cam we discard the traditional multipolar assumptions about the structure of magnetic fields in Ap stars and explore the stellar magnetic topology without introducing any global a priori constraints on the field structure. The complex magnetic model of 53 Cam derived with our magnetic Doppler imaging method achieves a good fit to the observed intensity, circular and linear polarization profiles of strong magnetically sensitive $\ion{Fe}{ii}$spectral lines. Such an agreement between observations and model predictions was not possible with any earlier multipolar magnetic models, based on modelling Stokes Ispectra and fitting surface averaged magnetic observables (e.g., longitudinal field, magnetic field modulus, etc.). Furthermore, we demonstrate that even the direct inversion of the four Stokes parameters of 53 Cam assuming a low-order multipolar magnetic geometry is incapable of achieving an adequate fit to our spectropolarimetric observations. Thus, as a main result of our investigation, we discover that the magnetic field topology of 53 Cam is considerably more complex than any low-order multipolar expansion, raising a general question about the validity of the multipolar assumption in the studies of magnetic field structures of Ap stars. In addition to the analysis of the magnetic field of 53 Cam, we reconstruct surface abundance distributions of Si, Ca, Ti, Fe and Nd. These abundance maps confirm results of the previous studies of 53 Cam, in particular dramatic antiphase variation of Ca and Ti abundances.

In this paper we report a new series of high-precision (median $\sigma_{\rm B}\sim 80$G) longitudinal magnetic field measurements of RR Lyrae, the brightest Blazhko star, obtained with the MuSiCoS spectropolarimeter over a period of almost 4 years from 1999-2002. These data provide no evidence whatsoever for a strong magnetic field in the photosphere of RR Lyrae, a result consistent with Preston's ([CITE]) results, but inconsistent with apparent magnetic field detections by Babcock ([CITE]) and Romanov et al. ([CITE], [CITE]). Following discussion of these disparate results, we conclude that RR Lyrae is a bona fide non-magnetic star, a conclusion which leads to the general falsification of models of the Blazkho effect requiring strong photospheric magnetic fields. Furthermore, due to the 4 year baseline of our observations, we can also dismiss the hypothesis that RR Lyrae undergoes a 4-year “magnetic cycle”. Therefore the origin of the observed 4–year modulation of RR Lyrae remains unexplained, and we stress the need for additional theoretical efforts to come to a better understanding of this phenomenon.

Two newly identified Ae stars, νCyg and κUMa, were discovered in the course of the Magnetic Survey of Bright main sequence stars (Monin et al. 2002). We present their Hαprofiles along with measurements of their equivalent width and parameters of emission features. Emission in the Hαline of νCyg is variable on a time scale of 3 years. κUMa exhibits weak emission which is rather stable. The emission is thought to arise from a circumstellar disk, and we have estimated the size of that disk.Both new emission stars are IRAS sources. Their IR color excesses are consistent with those of classical Ae stars. Thus, νCyg and κUMa appear not to belong to the class of Herbig Ae/Be stars. We argue that the frequency of Ae stars may be underestimated due to the difficulty of detection of weak emission in some A stars.

We have been searching for magnetic Ap stars in open clusters, in order to clarify the time evolution of magnetic fields in middle main sequence stars from the ZAMS to the TAMS. We have discovered that the star HD 66318 in the open cluster NGC 2516 has an extraordinarily large magnetic field: the measured mean longitudinal component $B_{\rm l} \approx 4.5$kG, and the mean field modulus $B_{\rm s} \approx 14.5$kG. This star thus has one of the largest fields so far discovered in a non-degenerate star, and the largest field known in a current Ap star cluster member.?We estimate that HD 66318 has completed about $16 \pm 5$% of its main sequence life. It thus appears to contradict the hypothesis of Hubrig et al. that magnetic fields are only found in stars that have completed at least 30% of their main sequence lifetimes.?There is no indication that the spectrum or brightness of the star is variable, and the spectral lines are very sharp. The star probably has a very long rotation period (years). ?We have modelled some parts of the observed spectrum, assuming that the chemical composition is uniform both horizontally and vertically, and using a simple multipolar expansion for the field structure; although our model does not reproduce exactly the observed spectrum, it is clear that the atmospheric chemical composition of the star is very peculiar, with Ti, Cr and Fe overabundant by between 1.5 and 2.5 dex. Both La iiand iiiare apparently about 4 dex overabundant. In contrast, evidence for the presence of other rare earths is difficult to find in the spectrum. It appears that Ce iii, Pr iii, Nd iiand iii, and Eu iiare detected with inferred overabundances ranging between 1.5 and 5 dex, but for most of these elements, the abundance of the non-detected ionization state is significantly lower than that inferred for the detected state. HD 66318 thus seems to exhibit strong discrepancies between abundances deduced for different ionization states of rare earths, a phenomenon so far found only in somewhat cooler stars. ?Even within one ionization state it has not been found possible to fit most observed lines with a single value of abundance. For example, when we fit medium strength lines of Fe ii, the calculated strong lines of this ion are deeper than observed, and the calculated weak lines are less deep than observed. This situation is probably due to strong vertical abundance stratification of most of the elements studied.?Finally, HD 66318 also shows a new form of core-wing anomaly in Hain which the observed line profile falls belowthe computed one in the core. These characteristics clearly suggest that the atmospheric structure of HD 66318 is not closely similar to that of a normal main sequence A star of similar parameters.?

It has been known for more than 70 years that synaptic strength is dynamically regulated in a use-dependent manner. At synapses with a low initial release probability, closely spaced presynaptic action potentials can result in facilitation, a short-term form of enhancement in which each subsequent action potential evokes greater neurotransmitter release. Facilitation can enhance neurotransmitter release considerably and can profoundly influence information transfer across synapses, but the underlying mechanism remains a mystery. One proposed mechanism is that a specialized calcium sensor for facilitation transiently increases the probability of release, and this sensor is distinct from the fast sensors that mediate rapid neurotransmitter release. Yet such a sensor has never been identified, and its very existence has been disputed. Here we show that synaptotagmin 7 (Syt7) is a calcium sensor that is required for facilitation at several central synapses. In Syt7-knockout mice, facilitation is eliminated even though the initial probability of release and the presynaptic residual calcium signals are unaltered. Expression of wild-type Syt7 in presynaptic neurons restored facilitation, whereas expression of a mutated Syt7 with a calcium-insensitive C2A domain did not. By revealing the role of Syt7 in synaptic facilitation, these results resolve a longstanding debate about a widespread form of short-term plasticity, and will enable future studies that may lead to a deeper understanding of the functional importance of facilitation.

Circular spectropolarimetric observations of 74 stars were obtained in an attempt to detect magnetic fields via the longitudinal Zeeman effect in their spectral lines. The sample observed includes 22 normal B, A and F stars, four emission-line B and A stars, 25 Am stars, 10 HgMn stars, two λBoo stars and 11 magnetic Ap stars. Using the Least-Squares Deconvolution multi-line analysis approach (Donati et al. [CITE]), high precision Stokes Iand Vmean signatures were extracted from each spectrum. We find absolutely no evidence for magnetic fields in the normal, Am and HgMn stars, with upper limits on longitudinal field measurements usually considerably smaller than any previously obtained for these objects. We conclude that if any magnetic fields exist in the photospheres of these stars, these fields are not ordered as in the magnetic Ap stars, nor do they resemble the fields of active late-type stars. We also detect for the first time a field in the A2pSr star HD 108945 and make new precise measurements of longitudinal fields in five previously known magnetic Ap stars, but do not detect fields in five other stars classified as Ap SrCrEu. We also report new results for several binary systems, including a new $v\sin i$for the rapidly rotating secondary of the Am-δDel SB2 HD 110951.

We report new high resolution Stokes Vspectropolarimetry and ultra-high precision longitudinal magnetic field measurements of the pulsating classical Cepheid ηAql which fail to corroborate the report by Plachinda ([CITE]) of a ~100 G magnetic field in this star.

This paper describes an experiment aimed at evaluating the capability of the FORS1instrument at the VLTfor measuring weak ($\simeq $0.1%) Zeeman circular polarization signatures in stellar H Balmer lines. We have obtained low-resolution polarized spectra at 3500–5800 Å of two bright A-type stars, HD 94660, and HD 96441. The former is a well known magnetic star, the latter an apparently non-magnetic, unpolarized star that was observed for comparison purposes. In order to test the possibility of performing multi-object spectropolarimetric measurements (e.g., for cluster studies), observations were taken both on-axis (i.e., at the CCD field center) and off-axis (i.e., at the edges of the CCD). In HD 94660 (the magnetic star), we detected a clear signal of circular polarization in all observed hydrogen Balmer lines (i.e., from Hβto the Balmer limit), with a typical peak-to-peak amplitude of about 0.8%. From the analysis of Stokes Vunder the weak-field approximation, we have estimated a mean longitudinal field of $-2085 \pm 85$G, a value fully consistent with previous studies of this star. Notably, we found that at wavelengths shorter than about 4100 Å, the polarization signal detected off-axis is about 20–30% smaller than that detected on-axis. No polarization due to the Zeeman effect was detected in the comparison star HD 96441, and we estimate that the contribution due to instrumental circular polarization is limited to the order of $0.01\%$. This experiment demonstrates the effectiveness of FORS1at the VLTas a tool for high-sensitivity diagnosis of the magnetic field in upper main sequence stars, providing the potential for measuring fields in fainter and more rapidly rotating stars than has previously been possible.

With the aim of establishing a benchmark for the detailed calculation of the polarised line profiles of magnetic stars, we describe an intercomparison of LTE Stokes profiles calculated using three independent, state-of-the-art magnetic spectrum synthesis codes: Cossam, ı10 and Zeeman2. We find, upon establishing a homogeneous basis for the calculations (identical definitions of the Stokes parameters and the magnetic and stellar reference frames, identical input model stellar atmosphere, identical input atomic data, and identical chemical element abundances and magnetic field distributions), that local and disc-integrated Stokes IQUVprofiles of Fe ${\scriptstyle {\rm II}} \lambda 4923.9$calculated using the three codes agree very well. For the illustrative case of disc-integrated profiles calculated for abundance $\log {n_{\rm Fe}}/{n_{\rm tot}}=-4.60$, dipole magnetic field intensity $B_{\rm d}=5$kG, and projected rotational velocity $v_{\rm e}\sin i=20$km s-1, Stokes Iprofiles (depth ∼40% of the continuum flux Ic) agree to within about 0.05% rms of Ic, Stokes Vprofiles (full amplitude ∼10% ) to within about 0.02% rms of Ic, and Stokes Qand Uprofiles (full amplitudes ∼2% ) at the sub-0.01% rms level. These differences are sufficiently small so as to allow for congruent interpretation of the best spectropolarimetric data available, as well as for any data likely to become available during the near future. This indicates that uncertainties in modeling Stokes profiles result overwhelmingly from uncertainties in input atomic and physical data, especially the state and structure of model stellar atmospheres.

We present a comparison of observed and calculated Stokes IQUVspectra of two well-known magnetic chemically peculiar stars, βCoronae Borealis and 53 Camelopardalis. The observed Stokes spectra were recently described by Wade et al. ([CITE]), and have been complemented with additional circularly polarized spectra obtained at the Special Astrophysical Observatory. The calculated spectra represent the predictions of new and previously published magnetic field models derived from the analysis of some surface averaged field estimates (e.g., longitudinal field, magnetic field modulus, etc.). We find that these magnetic models are not sufficient to account fully for the observed Stokes profiles -particularly remarkable is the disagreement between the predicted and observed Stokes Qand Uprofiles of 53 Cam. We suggest that this should be interpreted in terms of magnetic morphologies which are significantly more complex than the second-order multipolar expansions assumed in the models. However, it is clear that some of our inability to reproduce the detailed shapes of the Stokes IQUVprofiles is unrelated to the magnetic models. For many metallic ions, for both stars, we found it impossible to account for the strengths and shapes of the observed spectral line profiles when we adopted a unique value for the individual ion abundance. We suggest that this results from strongly non-uniform distributions of these ions as a function of optical depth (i.e., chemical stratification), a hypothesis that is supported by comparison with simple chemically stratified models.

Clinical trials have provided guidance in developing triggers for transfusing in the hemodynamically stable patient. These studies have identified that improved outcomes can be obtained in the massively transfused patient when platelets and fresh frozen plasma are transfused with packed red blood cells. Studies that characterize the complications of transfusions, such as transfusion-related acute lung injury and poor cancer-related outcomes, are discussed. Emerging data that characterize the risk factors associated with transfusion-related acute lung injury and suggest metastasis and local recurrence occur at a higher rate in the transfused patient are discussed. Hematologic disorders commonly encountered by surgeons are discussed.

We present in this paper the technical characteristics of a new polarimetric unit dedicated to the MuSiCoS échelle spectrograph. The first test runs indicate that our instrument is very good at measuring polarisation or depolarisation structures in line profiles. It is therefore one of the very few facilities worldwide for studying magnetic topologies of active and chemically peculiar stars through rotational modulation of linearly and circularly polarised Zeeman signatures in line profiles. It is also a very interesting tool for investigating geometries of non-axisymmetric circumstellar environments through depolarisation of spectral lines formed within the scattering envelope.

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, the brightness and temperature variations of stars generally brighter than mag(V) ? 4 with precision and time coverage not possible from the ground. The current mission design consists of six nanosats (hence Constellation): two from Austria, two from Canada, and two from Poland. Each 7 kg nanosat carries an optical telescope of aperture 3 cm feeding an uncooled CCD. One instrument in each pair is equipped with a blue filter; the other with a red filter. Each BRITE instrument has a wide field of view (?24°), so up to about 15 bright stars can be observed simultaneously, sampled in 32 × 32 pixels sub-rasters. Photometry of additional fainter targets, with reduced precision but thorough time sampling, will be possible through onboard data processing. The BRITE sample is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases. The goals of BRITE-Constellation are to (1) measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology; (2) look for varying spots on the stars surfaces carried across the stellar disks by rotation, which are the sources of co-rotating interaction regions in the winds of the most luminous stars, probably arising from magnetic subsurface convection; and (3) search for planetary transits.