cliff yau - Academia.edu (original) (raw)
Papers by cliff yau
Journal of Higher Education Policy and Management, 2012
Students' adjustment to the university environment is an important factor in predicting universit... more Students' adjustment to the university environment is an important factor in predicting university outcomes and is crucial to their future achievements. University support to students' transition to university life can be divided into three dimensions: academic adjustment, social adjustment and psychological adjustment. However, these relationships have not been studied simultaneously in previous studies. The purpose of this study is to examine the students' perception on the relationships between two of the three dimensions. The study is based on a survey of 265 students from five Hong Kong universities. The findings show that students perceive that (1) social adjustment has a positive impact on academic adjustment; (2) psychological adjustment has a positive impact on academic adjustment; and (3) social adjustment has a positive impact on psychological adjustment. The implications are explored and discussed.
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Journal of High Energy Physics, 2011
We construct flux-stabilised IIB compactifications whose extra dimensions (EDs) have very differe... more We construct flux-stabilised IIB compactifications whose extra dimensions (EDs) have very different sizes, and use these to describe several vacua with a TeV string scale. Because we can access regimes where 2 dimensions are hierarchically larger than the other 4, we find examples where 2 dimensions are micron-sized while the other 4 are at the weak scale in addition to standard examples with all 6 EDs equally large. Besides providing UV completeness, the phenomenology of these models is richer than vanilla large-dimensional models in several ways: (i) they are supersymmetric, with SUSY broken at sub-eV scales in the bulk but only nonlinearly realised in the SM sector, leading to no MSSM superpartners and many more bulk missing-energy channels, as in supersymmetric large extra dimensions (SLED); (ii) small cycles in the complicated extra-dimensional geometry allow some KK states to reside at TeV scales even if all 6 EDs are much larger; (iii) a rich spectrum of string and KK states at TeV scales; and (iv) an equally rich spectrum of light moduli having unusually small (but technically natural) masses, with potentially interesting implications for cosmology and astrophysics that nonetheless evade new-force constraints. The hierarchy problem is solved because the extra-dimensional volume is naturally stabilised at exponentially large values: the EDs are CY geometries with a 4D K3 or T^4-fibration over a 2D base, with moduli stabilised within the LARGE-Volume scenario. The new technical step is the use of poly-instanton corrections to the superpotential (which, unlike for simpler models, are likely to be present on K3 or T^4-fibered CY compactifications) to obtain a large hierarchy between the sizes of different dimensions. For several scenarios we identify the low-energy spectrum and briefly discuss some of their astrophysical, cosmological and phenomenological implications.
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Journal of High Energy Physics, 2011
Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo... more Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M KK , in extra-dimensional models, or the gravitino mass, M 3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M g , (e.g the string scale, M s , in string theory) is of order the Planck mass, \( {M_p} = \sqrt {{8\pi G}} \simeq {10^{18}} \) GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M g and M p is parameterized by the (large) size of the extra dimensional volume, \( \mathcal{V} \) (in string units), according to M p : M g : M KK : M 3/2 ∝ 1: \( {\mathcal{V}^{ - {{1} \left/ {2} \right.}}}:{\mathcal{V}^{ - {{2} \left/ {3} \right.}}}:{\mathcal{V}^{ - 1}} \) . We find that the generic size of quantum corrections to masses is of the order of M KK M 3/2/M p ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{5} \left/ {3} \right.}}}}} \right.} \) . The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M V ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{3} \left/ {2} \right.}}}}} \right.} \) ≪M 3/2 ≪M KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation.
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Phytoparasitica, 1997
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IEEE Transactions on Automatic Control, 2011
This technical note is concerned with exponential stability analysis of linear time-varying syste... more This technical note is concerned with exponential stability analysis of linear time-varying systems represented by the second-order vector differential equations with the singular leading coefficient matrix. Using bounding techniques on the trajectories of the linear time-varying systems, the stability problem of the time-varying systems is transformed to that of the time-invariant systems and a new sufficient condition for exponential stability
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Journal of High Energy Physics, 2007
Back-reaction effects can modify the dynamics of mobile D3 branes moving within type IIB vacua, i... more Back-reaction effects can modify the dynamics of mobile D3 branes moving within type IIB vacua, in a way which has recently become calculable. We identify some of the ways these effects can alter inflationary scenarios, with the following three results: (1) By examining how the forces on the brane due to moduli-stabilizing interactions modify the angular motion of D3 branes moving in Klebanov-Strassler type throats, we show how previous slow-roll analyses can remain unchanged for some brane trajectories, while being modified for other trajectories. These forces cause the D3 brane to sink to the bottom of the throat except in a narrow region close to the D7 brane, and do not ameliorate the \eta-problem of slow roll inflation in these throats; (2) We argue that a recently-proposed back-reaction on the dilaton field can be used to provide an alternative way of uplifting these compactifications to Minkowski or De Sitter vacua, without the need for a supersymmetry-breaking anti-D3 brane; and (3) by including also the D-term forces which arise when supersymmetry-breaking fluxes are included on D7 branes we identify the 4D supergravity interactions which capture the dynamics of D3 motion in D3/D7 inflationary scenarios. The form of these potentials sheds some light on recent discussions of how symmetries constrain D term interactions in the low-energy theory.
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Surgical Endoscopy and Other Interventional Techniques, 2006
Background A newly constructed Endoscopic-Laparoscopic operating room (Endo-Lap OR) started to op... more Background A newly constructed Endoscopic-Laparoscopic operating room (Endo-Lap OR) started to operate in our department in January 2005. A prospective study was conducted to evaluate its feasibility, efficacy, and safety, as well as the staff’s satisfaction. Patients and methods From January 2005 to September 2005, all patients undergoing operation in this Endo-Lap OR were included in the study. The patient’s diagnosis, types of operating procedures, incidents of operating failure (either due to the hardware or the software of Endo-Lap OR) that led to a delay in the patient’s transfer or that extended the total operating time were recorded. In addition, questionnaires regarding staff satisfaction with the new operating room were distributed to nurses, anesthetists, and surgeons. Results A total of 640 cases were included in the study period, 245 cases of open surgery, 282 cases of laparoscopic surgery, 82 cases of endoscopic surgery, 17 cases of video-assisted thoracoscopic surgery, and 14 cases of combined endoscopic-laparoscopic surgery. There were no reported incidents of operating failure related to hardware or software problems. The overall staff satisfaction was excellent. Conclusions The integration of endoscopic and laparoscopic surgery into this newly constructed Endo-Lap OR is feasible and safe. The running of the operating room was smooth and it received a high level of acceptance and satisfaction from different staff members.
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Tertiary Education and Management, 2012
The purpose of this study is to determine if there are gender differences in the perception of un... more The purpose of this study is to determine if there are gender differences in the perception of university support. The study is based on a survey of 368 students in a Hong Kong university. The findings of the study are threefold. First, female students perceive the university as being more supportive in their academic adjustment than do male students (t = −4.256, p < 0.001). Second, male students perceive the university as being more supportive in their social adjustment than do female students (t = 2.156, p < 0.05). Last, male students perceive the university as being more supportive in their psychological adjustment than do female students (t = 2.401, p < 0.05).
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Journal of Higher Education Policy and Management, 2012
Students' adjustment to the university environment is an important factor in predicting universit... more Students' adjustment to the university environment is an important factor in predicting university outcomes and is crucial to their future achievements. University support to students' transition to university life can be divided into three dimensions: academic adjustment, social adjustment and psychological adjustment. However, these relationships have not been studied simultaneously in previous studies. The purpose of this study is to examine the students' perception on the relationships between two of the three dimensions. The study is based on a survey of 265 students from five Hong Kong universities. The findings show that students perceive that (1) social adjustment has a positive impact on academic adjustment; (2) psychological adjustment has a positive impact on academic adjustment; and (3) social adjustment has a positive impact on psychological adjustment. The implications are explored and discussed.
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Journal of High Energy Physics, 2011
We construct flux-stabilised IIB compactifications whose extra dimensions (EDs) have very differe... more We construct flux-stabilised IIB compactifications whose extra dimensions (EDs) have very different sizes, and use these to describe several vacua with a TeV string scale. Because we can access regimes where 2 dimensions are hierarchically larger than the other 4, we find examples where 2 dimensions are micron-sized while the other 4 are at the weak scale in addition to standard examples with all 6 EDs equally large. Besides providing UV completeness, the phenomenology of these models is richer than vanilla large-dimensional models in several ways: (i) they are supersymmetric, with SUSY broken at sub-eV scales in the bulk but only nonlinearly realised in the SM sector, leading to no MSSM superpartners and many more bulk missing-energy channels, as in supersymmetric large extra dimensions (SLED); (ii) small cycles in the complicated extra-dimensional geometry allow some KK states to reside at TeV scales even if all 6 EDs are much larger; (iii) a rich spectrum of string and KK states at TeV scales; and (iv) an equally rich spectrum of light moduli having unusually small (but technically natural) masses, with potentially interesting implications for cosmology and astrophysics that nonetheless evade new-force constraints. The hierarchy problem is solved because the extra-dimensional volume is naturally stabilised at exponentially large values: the EDs are CY geometries with a 4D K3 or T^4-fibration over a 2D base, with moduli stabilised within the LARGE-Volume scenario. The new technical step is the use of poly-instanton corrections to the superpotential (which, unlike for simpler models, are likely to be present on K3 or T^4-fibered CY compactifications) to obtain a large hierarchy between the sizes of different dimensions. For several scenarios we identify the low-energy spectrum and briefly discuss some of their astrophysical, cosmological and phenomenological implications.
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Journal of High Energy Physics, 2011
Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo... more Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M KK , in extra-dimensional models, or the gravitino mass, M 3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M g , (e.g the string scale, M s , in string theory) is of order the Planck mass, \( {M_p} = \sqrt {{8\pi G}} \simeq {10^{18}} \) GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M g and M p is parameterized by the (large) size of the extra dimensional volume, \( \mathcal{V} \) (in string units), according to M p : M g : M KK : M 3/2 ∝ 1: \( {\mathcal{V}^{ - {{1} \left/ {2} \right.}}}:{\mathcal{V}^{ - {{2} \left/ {3} \right.}}}:{\mathcal{V}^{ - 1}} \) . We find that the generic size of quantum corrections to masses is of the order of M KK M 3/2/M p ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{5} \left/ {3} \right.}}}}} \right.} \) . The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M V ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{3} \left/ {2} \right.}}}}} \right.} \) ≪M 3/2 ≪M KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation.
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Phytoparasitica, 1997
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IEEE Transactions on Automatic Control, 2011
This technical note is concerned with exponential stability analysis of linear time-varying syste... more This technical note is concerned with exponential stability analysis of linear time-varying systems represented by the second-order vector differential equations with the singular leading coefficient matrix. Using bounding techniques on the trajectories of the linear time-varying systems, the stability problem of the time-varying systems is transformed to that of the time-invariant systems and a new sufficient condition for exponential stability
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Journal of High Energy Physics, 2007
Back-reaction effects can modify the dynamics of mobile D3 branes moving within type IIB vacua, i... more Back-reaction effects can modify the dynamics of mobile D3 branes moving within type IIB vacua, in a way which has recently become calculable. We identify some of the ways these effects can alter inflationary scenarios, with the following three results: (1) By examining how the forces on the brane due to moduli-stabilizing interactions modify the angular motion of D3 branes moving in Klebanov-Strassler type throats, we show how previous slow-roll analyses can remain unchanged for some brane trajectories, while being modified for other trajectories. These forces cause the D3 brane to sink to the bottom of the throat except in a narrow region close to the D7 brane, and do not ameliorate the \eta-problem of slow roll inflation in these throats; (2) We argue that a recently-proposed back-reaction on the dilaton field can be used to provide an alternative way of uplifting these compactifications to Minkowski or De Sitter vacua, without the need for a supersymmetry-breaking anti-D3 brane; and (3) by including also the D-term forces which arise when supersymmetry-breaking fluxes are included on D7 branes we identify the 4D supergravity interactions which capture the dynamics of D3 motion in D3/D7 inflationary scenarios. The form of these potentials sheds some light on recent discussions of how symmetries constrain D term interactions in the low-energy theory.
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Surgical Endoscopy and Other Interventional Techniques, 2006
Background A newly constructed Endoscopic-Laparoscopic operating room (Endo-Lap OR) started to op... more Background A newly constructed Endoscopic-Laparoscopic operating room (Endo-Lap OR) started to operate in our department in January 2005. A prospective study was conducted to evaluate its feasibility, efficacy, and safety, as well as the staff’s satisfaction. Patients and methods From January 2005 to September 2005, all patients undergoing operation in this Endo-Lap OR were included in the study. The patient’s diagnosis, types of operating procedures, incidents of operating failure (either due to the hardware or the software of Endo-Lap OR) that led to a delay in the patient’s transfer or that extended the total operating time were recorded. In addition, questionnaires regarding staff satisfaction with the new operating room were distributed to nurses, anesthetists, and surgeons. Results A total of 640 cases were included in the study period, 245 cases of open surgery, 282 cases of laparoscopic surgery, 82 cases of endoscopic surgery, 17 cases of video-assisted thoracoscopic surgery, and 14 cases of combined endoscopic-laparoscopic surgery. There were no reported incidents of operating failure related to hardware or software problems. The overall staff satisfaction was excellent. Conclusions The integration of endoscopic and laparoscopic surgery into this newly constructed Endo-Lap OR is feasible and safe. The running of the operating room was smooth and it received a high level of acceptance and satisfaction from different staff members.
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Tertiary Education and Management, 2012
The purpose of this study is to determine if there are gender differences in the perception of un... more The purpose of this study is to determine if there are gender differences in the perception of university support. The study is based on a survey of 368 students in a Hong Kong university. The findings of the study are threefold. First, female students perceive the university as being more supportive in their academic adjustment than do male students (t = −4.256, p < 0.001). Second, male students perceive the university as being more supportive in their social adjustment than do female students (t = 2.156, p < 0.05). Last, male students perceive the university as being more supportive in their psychological adjustment than do female students (t = 2.401, p < 0.05).
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