371 research outputs found
On the monotonicity principle of optimal Skorokhod embedding problem
In this paper, we provide an alternative proof of the monotonicity principle
for the optimal Skorokhod embedding problem established by Beiglb\"ock, Cox and
Huesmann. This principle presents a geometric characterization that reflects
the desired optimality properties of Skorokhod embeddings. Our proof is based
on the adaptation of the Monge-Kantorovich duality in our context together with
a delicate application of the optional cross-section theorem and a clever
conditioning argument
Optimal Skorokhod embedding under finitely-many marginal constraints
The Skorokhod embedding problem aims to represent a given probability measure
on the real line as the distribution of Brownian motion stopped at a chosen
stopping time. In this paper, we consider an extension of the optimal Skorokhod
embedding problem to the case of finitely-many marginal constraints. Using the
classical convex duality approach together with the optimal stopping theory, we
obtain the duality results which are formulated by means of probability
measures on an enlarged space. We also relate these results to the problem of
martingale optimal transport under multiple marginal constraints
Tightness and duality of martingale transport on the Skorokhod space
The martingale optimal transport aims to optimally transfer a probability
measure to another along the class of martingales. This problem is mainly
motivated by the robust superhedging of exotic derivatives in financial
mathematics, which turns out to be the corresponding Kantorovich dual. In this
paper we consider the continuous-time martingale transport on the Skorokhod
space of cadlag paths. Similar to the classical setting of optimal transport,
we introduce different dual problems and establish the corresponding dualities
by a crucial use of the S-topology and the dynamic programming principle
Words from a Brick in the Wall (Or, What the Dialectical Poet Tries to Say But Fails to Say, and What He Might Whistle or Sing)
This is the manifesto from the end of my novel I am China. The novel is about a Chinese punk musician in exile in the west and his love and hate relation to the state as well as his relationship with his poetess lover in China. The novel is written in an epistolary form – in the story the letters and diaries are discovered by an English literary translator from Britain. The manifesto is supposed to be written by the musician Kublai Jian, and focuses on the political nature of being an artist in this world and the possibility/impossibility of revolution. The manifesto suggests that a true artist is committed to perpetual revolution
Simulation and Design of an UWB Imaging System for Breast Cancer Detection
Breast cancer is the most frequently diagnosed cancer among women. In recent
years, the mortality rate due to this disease is greatly decreased thanks to both
enormous progress in cancer research, and screening campaigns which have allowed
the increase in the number of early diagnoses of the disease. In fact, if the tumor is
identied in its early stage, e.g. when it has a diameter of less than one centimeter,
the possibility of a cure can reach 93%. However, statistics show that more young
aged women are suered breast cancer.
The goal of screening exams for early breast cancer detection is to nd cancers
before they start to cause symptoms. Regular mass screening of all women at risk
is a good option to achieve that. Instead of meeting very high diagnostic standards,
it is expected to yield an early warning, not a denitive diagnosis. In the last
decades, X-ray mammography is the most ecient screening technique. However,
it uses ionizing radiation and, therefore, should not be used for frequent check-ups.
Besides, it requires signicant breast compression, which is often painful. In this
scenario many alternative technologies were developed to overcome the limitations
of mammography. Among these possibilities, Magnetic Resonance Imaging (MRI)
is too expensive and time-consuming, Ultrasound is considered to be too operatordependent
and low specicity, which are not suitable for mass screening. Microwave
imaging techniques, especially Ultra WideBand (UWB) radar imaging, is the most
interesting one. The reason of this interest relies on the fact that microwaves are
non-ionizing thus permitting frequent examinations. Moreover, it is potentially lowcost
and more ecient for young women. Since it has been demonstrated in the
literatures that the dielectric constants between cancerous and healthy tissues are
quite dierent, the technique consists in illuminating these biological tissues with
microwave radiations by one or more antennas and analyzing the re
ected signals.
An UWB imaging system consists of transmitters, receivers and antennas for
the RF part, the transmission channel and of a digital backend imaging unit for
processing the received signals. When an UWB pulse strikes the breast, the pulse is
re
ected due to the dielectric discontinuity in tissues, the bigger the dierence, the
bigger the backscatter. The re
ected signals are acquired and processed to create
the energy maps. This thesis aims to develop an UWB system at high resolution for the detection of carcinoma breast already in its initial phase. To favor the adoption
of this method in screening campaigns, it is necessary to replace the expensive and
bulky RF instrumentation used so far with ad-hoc designed circuits and systems.
In order to realize that, at the very beginning, the overall system environment must
be built and veried, which mainly consists of the transmission channel{the breast
model and the imaging unit. The used transmission channel data come from MRI
of the prone patient. In order to correctly use this numerical model, a simulator was
built, which was implemented in Matlab, according to the Finite-Dierence-Time-
Domain (FDTD) method. FDTD algorithm solves the electric and magnetic eld
both in time and in space, thus, simulates the propagation of electromagnetic waves
in the breast model. To better understand the eect of the system non-idealities,
two 2D breast models are investigated, one is homogeneous, the other is heterogeneous.
Moreover, the modeling takes into account all critical aspects, including
stability and medium dispersion. Given the types of tissues under examination, the
frequency dependence of tissue dielectric properties is incorporated into wideband
FDTD simulations using Debye dispersion parameters. A performed further study
is in the implementation of the boundary conditions. The Convolution Perfectly
Matched Layer (CPML) is used to implement the absorbing boundaries.
The objective of the imaging unit is to obtain an energy map representing the
amount of energy re
ected from each point of the breast, by recombining the sampled
backscattered signals. For this purpose, the study has been carried out on various
beamforming in the literature. The basic idea is called as "delay and sum", which
is to align the received signals in such a way as to focus a given point in space and
then add up all the contributions, so as to obtain a constructive interference at that
point if this is a diseased tissue. In this work, Microwave Imaging via Space Time
(MIST) Beamforming algorithm is applied, which is based on the above principle
and add more elaborations of the signals in order to make the algorithm less sensitive
to propagation phenomena in the medium and to the non-idealities of the system.
It is divided into two distinct steps: the rst step, called SKin Artifact Removal
(SKAR), takes care of removing the contributions from the signal caused by the
direct path between the transmitter and receiver, the re
ection of skin, as they are
orders of magnitude higher compared to the re
ections caused by cancers; the second
step, which is BEAmForming (BEAF), performs the algorithm of reconstruction by
forming a weighted combination of time delayed version of the calibrated re
ected
signals.
As discussed above, more attention must be paid on the implementation of the
ad-hoc integration circuits. In this scenario, due to the strict requirements on the
RF receiver component, two dierent approaches of the implementation of the RF
front-end, Direct Conversion (DC) receiver and Coherent Equivalent Time Sampling
(CETS) receiver are compared. They are modeled behaviorally and the eects of
various impairments, such as thermal, jitter, and phase noise, as well as phase inaccuracies, non-linearity, ADC quantization noise and distortion, on energy maps
and on quantitative metrics such as SCR and SMR are evaluated. Dierential
Gaussian pulse is chosen as the exciting source. Results show that DC receiver
performs higher sensitivity to phase inaccuracies, which makes it less robust than
the CETS receiver. Another advantage of the CETS receiver is that it can work
in time domain with UWB pulses, other than in frequency domain with stepped
frequency continuous waves like the DC one, which reduces the acquisition time
without impacting the performance.
Based on the results of the behavioral simulations, low noise amplier (LNA)
and Track and Hold Amplier (THA) can be regarded as the most critical parts
for the proposed CETS receiver, as well as the UWB antenna. This work therefore
focuses on their hardware implementations. The LNA, which shows critical performance
limitation at bandwidth and noise gure of receiver, has been developed based
on common-gate conguration. And the THA based on Switched Source Follower
(SSF) scheme has been presented and improved to obtain high input bandwidth,
high sampling rate, high linearity and low power consumption. LNA and THA
are implemented in CMOS 130nm technology and the circuit performance evaluation
has been taken place separately and together. The small size UWB wide-slot
antenna is designed and simulated in HFSS.
Finally, in order to evaluate the eect of the implemented transistor level components
on system performance, a multi-resolution top-down system methodology
is applied. Therfore, the entire
ow is analyzed for dierent levels of the RF frontend.
Initially the system components are described behaviorally as ideal elements.
The main activity consists in the analysis and development of the entire frontend
system, observing and complementing each other blocks in a single
ow simulation,
clear and well-dened in its various interfaces. To achieve that the receiver is modeled
and analyzed using VHDL-AMS language block by block, moreover, the impact
of quantization, noise, jitter, and non-linearity is also evaluated. At last, the behavioral
description of antenna, LNA and THA is replaced with a circuit-level one
without changing the rest of the system, which permits a system-level assessment
of low-level issues
Alumni: Another Piece of the Puzzle - The Study of Alumni Service Quality in a New Zealand Academic Library
Alumni are recognized as one of the academic library user groups although traditionally alumni were only considered as donors. This paper briefly reviewed the background of alumni studies and library service quality studies. According to the previous research, there is an absence of studies about alumni’s expectation and perception toward library services. A better understanding of alumni library memberships’ service quality can help the library to develop more suitable services and programmes for alumni, which is beneficial to the library, the alumni office and the university.
This research measured the service quality of library alumni service in three dimensions, reliability, library staff and library resources. The results indicated alumni are mostly comfortable with the library services. Reliability was the most important service quality dimension which received the highest rating from alumni. The result also suggested that alumni expect the library membership package to provide access to a bigger collection of e-journals and databases
Comparison between transgenic maize with exotic betaine aldehyde dehydrogenase (BADH) gene and its untransformed counterpart
We investigated the performance of a transgenic maize (Zea mays L) line with an exotic betaine aldehyde dehydrogenase (BADH) gene and its untransformed counterpart under drought and normal water conditions. Membrane permeability, osmoprotectant contents, and antioxidant enzyme activities of the maize lines as well as plant height and biomass were compared. The results showed that, under drought stress, compared with the untransgenic line, the contents of glycine betaine (GB), soluble sugars, soluble proteins and proline of the trans- genic line were significantly higher, so was the peroxidase (POD) activity; the contents of superoxide anion free radical, malondialdehyde (MDA) and the electrical conductivity of the transgenic line were lower; plant height and the biomass of the transgenic line were significantly higher. Under normal water conditions, the contents of soluble protein and MDA content of the transgenic line were significantly lower; but it was not the case for the content of superoxide anion free radical, electrical conductivity and superoxide dismutase (SOD) activity. No significant difference was observed in GB content and, the plant height and the biomass between the 2 lines. We conclude that the transgenic maize with exotic BADH gene was superior over its untransformed counterpart under drought stress and they performed similarly under normal water conditions
Analysis of characteristics of infectious pathogens in malignant tumors combined with bloodstream infection and significance of serum glucose detection
Background and purpose: The incidence rate of bloodstream infection (BSI) in patients with malignant tumor increases gradually with the progress of anti-tumor treatment. The treatment outcome is closely related to the infection of pathogen. At the same time, blood glucose also has a significant impact on the occurrence and development of the disease in this type of patients. This research aimed to retrospectively analyze the distribution characteristics of infectious pathogens isolated in patients with malignant tumors combined with bloodstream infection, the significance of serum glucose detection and prognostic value of its variation trend. Methods: Data of 434 malignant tumor patients with BSI and 409 patients without BSI treated in Fudan University Shanghai Cancer Center were retrospectively analyzed in this research. We utilized SPSS 26.0, Graphpad, Medcalc and Office software etc. to statistically analyze all the data covering clinical characteristics, infectious pathogens and biochemical parameters which were collected from Oct. 2019 to Dec. 2022. Results: The top three isolates in malignant tumor patients with BSI were Escherichia coli (29.4%), Klebsiella pneumoniae (13.8%) and Pseudomonas aeruginosa (4.8%). There were two or more mixed pathogenic bacteria in 8.5% patients. There were totally 100 deadly strains, among which the top three isolates were Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, accounting for 21.0%, 12.0% and 10.0% of the diseases, respectively. Survival analysis showed that mixed infection had a poorer prognosis compared to single infection (P=0.000). The fasting blood glucose level at the initial stage of symptoms was significantly higher in malignant tumor patients with BSI (median 7.39 mmol/L, interquartile range 5.95-9.88 mmol/L) than in tumor patients without BSI (median 5.97 mmol/L, interquartile range 5.25-7.06 mmol/L, P=0.000). The area under curve (AUC) of the receiver operating characteristic (ROC) curve of the patients with BSI determined by the fasting glucose level at the beginning of the disease was 0.718, which was higher compared with procalcitonin (PCT), the classic diagnostic marker (AUC=0.708). The combination of these two parameters could even improve diagnostic efficiency (AUC=0.761). Furthermore, survival analysis showed that the prognosis of patients with high level of fasting glucose at the beginning of BSI was poor (HR=3.067, 95% CI: 1.375-6.838, P=0.000). In addition, the greater the glycemic variability at the beginning of BSI, the higher the risk of death was shown (HR=2.150, 95% CI: 1.125-4.109, P<0.01). Conclusion: It is suggested that patients with clinically suspected BSI should use antibiotics based on the distribution of isolates, and glucose levels should be monitored to access the infection early so as to take timely intervention and obtain greater treatment benefits
Automatic interictal epileptiform discharge (IED) detection based on convolutional neural network (CNN)
Clinical diagnosis of epilepsy significantly relies on identifying interictal epileptiform discharge (IED) in electroencephalogram (EEG). IED is generally interpreted manually, and the related process is very time-consuming. Meanwhile, the process is expert-biased, which can easily lead to missed diagnosis and misdiagnosis. In recent years, with the development of deep learning, related algorithms have been used in automatic EEG analysis, but there are still few attempts in IED detection. This study uses the currently most popular convolutional neural network (CNN) framework for EEG analysis for automatic IED detection. The research topic is transferred into a 4-labels classification problem. The algorithm is validated on the long-term EEG of 11 pediatric patients with epilepsy. The computational results confirm that the CNN-based model can obtain high classification accuracy, up to 87%. The study may provide a reference for the future application of deep learning in automatic IED detection
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