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Papers by Tomas James

The Astrophysical Journal, 2021

We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 2... more We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 272 and 375 GHz toward Sgr A*'s circumnuclear disk (CND). Our data comprise eight individual pointings, with significant SiO (87–76) and SO (7–6) emission detected toward 98 positions within these pointings. Additionally, we identify H2CS (91,9–81,8), OCS (25–24), and CH3OH (21,1–20,2) toward a smaller subset of positions. By using the observed peak line flux density, together with a Bayesian inference technique informed by radiative transfer models, we systematically recover the physical gas conditions toward each of these positions. We estimate that the bulk of the surveyed gas has temperature T kin < 500 K and density n H ⪅ 106 cm−3, consistent with previous studies of similar positions as traced by HCN clumps. However, we identify an uncharacteristically hot (T kin ≈ 600 K) and dense (n H ≈ 106 cm−3) source in the Northeastern Arm. This position is found to be approximately con...

Deepfake content — typically a video whose subject has been faceswapped — poses a real and growin... more Deepfake content — typically a video whose subject has been faceswapped — poses a real and growing threat to online security, both from a political and consumer-centric perspective. To assess the risk that this content has, as well as how straightforward it would be for an attacker to produce deepfaked content, we produce an example deepfake using two leading open-source frameworks, as well as an open-source facial synthesis model before evaluating each framework’s results and effectiveness. We subsequently suggest risk mitigation techniques, as well as deepfake detection methods. Our demonstrations show that, whilst technologically impressive, deepfaked content produced on consumer computing hardware are not truly realistic. However, this content can be impactful and pose a threat should it be produced by an experienced and motivated user with access to a high-end GPU. To combat this, we suggest content is marked prominently with a watermark and that detection techniques, such as f...

Astronomy & Astrophysics, Jan 29, 2020

Aims. The physical structure of a shock wave may take a form unique to its shock type, implying t... more Aims. The physical structure of a shock wave may take a form unique to its shock type, implying that the chemistry of each shock type is unique as well. We aim to investigate the different chemistries of J-type and C-type shocks in order to identify unique molecular tracers of both shock types. We apply these diagnostics to the protostellar outflow L1157 to establish whether the B2 clump could host shocks exhibiting type-specific behaviour. Of particular interest is the L1157-B2 clump, which has been shown to exhibit bright emission in S-bearing species and HNCO. Methods. We simulate, using a parameterised approach, a planar, steady-state J-type shock wave using UCLCHEM. We compute a grid of models using both C-type and J-type shock models to determine the chemical abundance of shock-tracing species as a function of distance through the shock and apply it to the L1157 outflow. We focus on known shock-tracing molecules such as H 2 O, HCN, and CH 3 OH. Results. We find that a range of molecules including H 2 O and HCN have unique behaviour specific to a J-type shock, but that such differences in behaviour are only evident at low v s and low n H. We find that CH 3 OH is enhanced by shocks and is a reliable probe of the pre-shock gas density. However, we find no difference between its gas-phase abundance in C-type and J-type shocks. Finally, from our application to L1157, we find that the fractional abundances within the B2 region are consistent with both C-type and J-type shock emission.

The Astrophysical Journal, 2021

We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 2... more We report subarcsecond Atacama Large Millimeter/submillimeter Array (ALMA) observations between 272 and 375 GHz toward Sgr A*'s circumnuclear disk (CND). Our data comprise eight individual pointings, with significant SiO (87–76) and SO (7–6) emission detected toward 98 positions within these pointings. Additionally, we identify H2CS (91,9–81,8), OCS (25–24), and CH3OH (21,1–20,2) toward a smaller subset of positions. By using the observed peak line flux density, together with a Bayesian inference technique informed by radiative transfer models, we systematically recover the physical gas conditions toward each of these positions. We estimate that the bulk of the surveyed gas has temperature T kin < 500 K and density n H ⪅ 106 cm−3, consistent with previous studies of similar positions as traced by HCN clumps. However, we identify an uncharacteristically hot (T kin ≈ 600 K) and dense (n H ≈ 106 cm−3) source in the Northeastern Arm. This position is found to be approximately con...

Deepfake content — typically a video whose subject has been faceswapped — poses a real and growin... more Deepfake content — typically a video whose subject has been faceswapped — poses a real and growing threat to online security, both from a political and consumer-centric perspective. To assess the risk that this content has, as well as how straightforward it would be for an attacker to produce deepfaked content, we produce an example deepfake using two leading open-source frameworks, as well as an open-source facial synthesis model before evaluating each framework’s results and effectiveness. We subsequently suggest risk mitigation techniques, as well as deepfake detection methods. Our demonstrations show that, whilst technologically impressive, deepfaked content produced on consumer computing hardware are not truly realistic. However, this content can be impactful and pose a threat should it be produced by an experienced and motivated user with access to a high-end GPU. To combat this, we suggest content is marked prominently with a watermark and that detection techniques, such as f...

Astronomy & Astrophysics, Jan 29, 2020

Aims. The physical structure of a shock wave may take a form unique to its shock type, implying t... more Aims. The physical structure of a shock wave may take a form unique to its shock type, implying that the chemistry of each shock type is unique as well. We aim to investigate the different chemistries of J-type and C-type shocks in order to identify unique molecular tracers of both shock types. We apply these diagnostics to the protostellar outflow L1157 to establish whether the B2 clump could host shocks exhibiting type-specific behaviour. Of particular interest is the L1157-B2 clump, which has been shown to exhibit bright emission in S-bearing species and HNCO. Methods. We simulate, using a parameterised approach, a planar, steady-state J-type shock wave using UCLCHEM. We compute a grid of models using both C-type and J-type shock models to determine the chemical abundance of shock-tracing species as a function of distance through the shock and apply it to the L1157 outflow. We focus on known shock-tracing molecules such as H 2 O, HCN, and CH 3 OH. Results. We find that a range of molecules including H 2 O and HCN have unique behaviour specific to a J-type shock, but that such differences in behaviour are only evident at low v s and low n H. We find that CH 3 OH is enhanced by shocks and is a reliable probe of the pre-shock gas density. However, we find no difference between its gas-phase abundance in C-type and J-type shocks. Finally, from our application to L1157, we find that the fractional abundances within the B2 region are consistent with both C-type and J-type shock emission.