Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in Laser Wire-Based Directed Energy Deposition

A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser wire-based directed energy deposition is demonstrated with a novel modification, i.e., site-specific changes to the controller setpoint were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary three-dimensional (3D) printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as extra-toolpath geometry and is fundamentally different from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed

Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in LaserWire-Based Directed Energy Deposition

A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser wire-based directed energy deposition is demonstrated with a novel modification, i.e., site-specific changes to the controller setpoint were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary three-dimensional (3D) printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as extra-toolpath geometry and is fundamentally dierent from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed

The published research paper: is it an important indicator of successful operational research at programme level?

Is a published research paper an important indicator of successful operational research at programme level in low-income countries? In academia, publishing in peer-reviewed scientific journals is highly encouraged and strongly pursued for academic recognition and career progression. In contrast, for those who engage in operational research at programme level, there is often no necessity or reward for publishing the results of research studies; it may even be criticized as being an unnecessary detraction from programme-related work. We present arguments to support publishing operational research from low-income countries; we highlight some of the main reasons for failure of publication at programme level and suggest ways forward

Cross-sectional study of approaches to diagnosis and management of dogs with immune-mediated haemolytic anaemia in primary care and referral veterinary practices in the United Kingdom.

ObjectivesTo determine whether veterinarians in primary care practices (PCPs) and board-certified clinicians (BCCs) approach treatment of dogs with immune-mediated haemolytic anaemia (IMHA) similarly, and whether practitioners with more experience treat similarly to those with less experience. We hypothesised those in PCPs would show more variation in their approach to similar cases than BCCs.MethodsA cross-sectional study was conducted by distributing a questionnaire to BCCs and veterinarians in PCPs. The questionnaire included direct questions and a number of clinical scenarios intended to capture approaches to common treatment problems.ResultsQuestionnaire responses were received from 241 veterinarians, including 216 in PCPs and 25 BCCs. Veterinarians in both settings used similar tests for diagnosis of IMHA, but BCCs performed more tests to exclude underlying causes of 'associative' disease. All veterinarians reported use of similar initial dosages of glucocorticoids (median 2 mg/kg per day in both groups, p = 0.92) but those used by more experienced practitioners were higher than those with less experience. Most veterinarians made allowances for the weight of dogs, using lower prednisolone dosages in a clinical scenario involving a 40 kg dog compared to a 9 kg dog (p = 0.025 for PCP, p = 0.002 for BCC). BCCs reported greater use of combinations of immunosuppressive drugs (pConclusionsApproaches to treatment of dogs with IMHA differ between BCCs and those in PCP. These differences may affect design and implementation of future research studies and clinical guidelines

Spectropolarimetry of the Classical T Tauri Star TW Hydrae

We present high resolution (R ~ 60,000) circular spectropolarimetry of the classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines and measure the net longitudinal magnetic field for 6 consecutive nights. While no net polarization is detected the first five nights, a significant photospheric field of Bz = 149 \pm 33 G is found on the sixth night. To rule out spurious instrumental polarization, we apply the same analysis technique to several non-magnetic telluric lines, detecting no significant polarization. We further demonstrate the reality of this field detection by showing that the splitting between right and left polarized components in these 12 photospheric lines shows a linear trend with Lande g-factor times wavelength squared, as predicted by the Zeeman effect. However, this longitudinal field detection is still much lower than that which would result if a pure dipole magnetic geometry is responsible for the mean magnetic field strength of 2.6 kG previously reported for TW Hya. We also detect strong circular polarization in the He I 5876 and the Ca II 8498 emission lines, indicating a strong field in the line formation region of these features. The polarization of the Ca II line is substantially weaker than that of the He I line, which we interpret as due to a larger contribution to the Ca II line from chromospheric emission in which the polarization signals cancel. However, the presence of polarization in the Ca II line indicates that accretion shocks on Classical T Tauri stars do produce narrow emission features in the infrared triplet lines of Calcium.Comment: One tar file. The paper has 22 pages, 5 figures. Accepted by AJ on Sep 10, 200

The Magnetic Fields of Classical T Tauri Stars

We report new magnetic field measurements for 14 classical T Tauri stars (CTTSs). We combine these data with one previous field determination in order to compare our observed field strengths with the field strengths predicted by magnetospheric accretion models. We use literature data on the stellar mass, radius, rotation period, and disk accretion rate to predict the field strength that should be present on each of our stars according to these magnetospheric accretion models. We show that our measured field values do not correlate with the field strengths predicted by simple magnetospheric accretion theory. We also use our field strength measurements and literature X-ray luminosity data to test a recent relationship expressing X-ray luminosity as a function of surface magnetic flux derived from various solar feature and main sequence star measurements. We find that the T Tauri stars we have observed have weaker than expected X-ray emission by over an order of magnitude on average using this relationship. We suggest the cause for this is actually a result of the very strong fields on these stars which decreases the efficiency with which gas motions in the photosphere can tangle magnetic flux tubes in the corona.Comment: 25 pages, 5 figure

A comparison of incompressible limits for resistive plasmas

The constraint of incompressibility is often used to simplify the magnetohydrodynamic (MHD) description of linearized plasma dynamics because it does not affect the ideal MHD marginal stability point. In this paper two methods for introducing incompressibility are compared in a cylindrical plasma model: In the first method, the limit $\gamma \to \infty$ is taken, where $\gamma$ is the ratio of specific heats; in the second, an anisotropic mass tensor $\mathbf{\rho}$ is used, with the component parallel to the magnetic field taken to vanish, $\rho_{\parallel} \to 0$. Use of resistive MHD reveals the nature of these two limits because the Alfv\'en and slow magnetosonic continua of ideal MHD are converted to point spectra and moved into the complex plane. Both limits profoundly change the slow-magnetosonic spectrum, but only the second limit faithfully reproduces the resistive Alfv\'en spectrum and its wavemodes. In ideal MHD, the slow magnetosonic continuum degenerates to the Alfv\'en continuum in the first method, while it is moved to infinity by the second. The degeneracy in the first is broken by finite resistivity. For numerical and semi-analytical study of these models, we choose plasma equilibria which cast light on puzzling aspects of results found in earlier literature.Comment: 14 pages, 10 figure

Maximum gravitational-wave energy emissible in magnetar flares

Recent searches of gravitational-wave (GW) data raise the question of what maximum GW energies could be emitted during gamma-ray flares of highly magnetized neutron stars (magnetars). The highest energies (\sim 10^{49} erg) predicted so far come from a model [K. Ioka, Mon. Not. Roy. Astron. Soc. 327, 639 (2001)] in which the internal magnetic field of a magnetar experiences a global reconfiguration, changing the hydromagnetic equilibrium structure of the star and tapping the gravitational potential energy without changing the magnetic potential energy. The largest energies in this model assume very special conditions, including a large change in moment of inertia (which was observed in at most one flare), a very high internal magnetic field, and a very soft equation of state. Here we show that energies of 10^{48}-10^{49} erg are possible under more generic conditions by tapping the magnetic energy, and we note that similar energies may also be available through cracking of exotic solid cores. Current observational limits on gravitational waves from magnetar fundamental modes are just reaching these energies and will beat them in the era of advanced interferometers.Comment: 16 pages, 5 figures, 1 tabl

Hydromagnetic Instability in Differentially Rotating Flows

We study the stability of a compressible differentially rotating flows in the presence of the magnetic field, and we show that the compressibility profoundly alters the previous results for a magnetized incompressible flow. The necessary condition of newly found instability can be easily satisfied in various flows in laboratory and astrophysical conditions and reads $B_{s} B_{\phi} \Omega' \neq 0$ where $B_{s}$ and $B_{\phi}$ are the radial and azimuthal components of the magnetic field, $\Omega' = d \Omega/ds$ with $s$ being the cylindrical radius. Contrary to the well-known magnetorotational instability that occurs only if $\Omega$ decreases with $s$, the instability considered in this paper may occur at any sign of $\Omega'$. The instability can operate even in a very strong magnetic field which entirely suppresses the standard magnetorotational instability. The growth time of instability can be as short as few rotation periods.Comment: 5 pages, 3 figure