This study reports on negative group velocities in a lumped transmission line, where capacitors and inductors connected to resistors are placed in the series and shunt branches of the periodic line, ...respectively. The propagation characteristics of the left-handed transmission line are examined along with two methods. The first method consists of analysing the lumped-element ladder network by solving in the time domain a system of differential equations derived from the Kirchhoff's voltage and current laws. In the second method, transmission matrix of the unit cell is applied to obtain the dispersion diagram from which the time group delay induced by the periodic network is derived as a function of frequency. Also, non-analytical input signals are considered, whereby transient effects occur at both ends of modulated half-sine wave packets propagating under negative group delay (NGD) regime of the left-handed line. NGD effects arise from ohmic dissipation due to the resistors which establish a frequency range in which NGD propagation is allowed. This finding is numerically demonstrated by injecting into the line modulated Gaussian wave packets, for which the negative time delays determined from the numerical solution of circuit equations and from the dispersion relation are in good agreement.
Purpose: Our study was designed to determine ophthalmologists' dexterity in performing standard ophthalmic procedures at various levels of expertise via a structured questionnaire. Methods: A ...structured questionnaire was administered via the Google platform from August 20 to September 19, 2022, to assess the perspectives and preferences of ophthalmologists concerning their proficiency in using their right hand, left hand, or both hands to perform routine tasks required in the practice of ophthalmic medicine and surgery. Results: Two hundred and three participants took part in the survey. A majority (n = 162, 79.8%) of the clinicians considered themselves right-handed, nine (4.4%) considered themselves left-handed, and 32 (15.7%) considered themselves ambidextrous. Also, 86% (n = 174) of the participants considered ambidexterity an essential trait in the practice of ophthalmic medicine and surgery. The number of cataract surgeries performed had an impact on the comfort of using both hands for performing anterior vitrectomy (P < 0.001), injection of viscoelastic (P < 0.001), and toric marking (P < 0.05), but not on the performance of capsulorhexis and switching of foot pedals. The number of procedures carried out had an impact on the comfort of using both hands in gonioscopy (P < 0.001), 90 D evaluation (P < 0.001), and 20 D evaluation (P < 0.05). More years of experience had an impact on skills involving the use of both hands for slit lamp joystick usage (P < 0.05) and laser procedures (P < 0.001). Conclusion: Irrespective of a person's handedness, trained ambidexterity in the required fields is achievable and has a significant impact on one's ability to perform the required skill optimally and appropriately.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
We consider the transverse electric (TE) plasmonic modes supported by black phosphorene (BP) in a parallel waveguide structure with left-handed material (LHM) instead of the conventional ...right-handed dielectric material. The existence condition of the TE BP surface plasmon polariton (SPP) is
I
m
σ
>
0
. When an electric field is polarized along one of the two orthogonal crystal axes, the anisotropic symmetric and anti-symmetric plasmonic modes depend on the incident optical energy, the chemical potential, and the distance between two BP sheets can be observed. The symmetric mode has a more extensive effective refractive index, which possesses stronger field confinement. With a decreasing distance
d
between two BP sheets, the coupling strength between the two separate BPSPP waves increases. When
d
is small enough, the anti-symmetric mode root does not exist. LHMs can be used to realize a TE BPSPP mode to enhance the localization of the BPSPP, which is a practical method in optoelectronic devices based on black phosphorene.
A coplanar waveguide‐fed ultra‐wideband (UWB) composite right/left‐handed (CRLH) antenna is presented. It is designed by embedding CRLH unit‐cell on the top side and split‐ring resonator (SRR) on the ...bottom side of FR4 epoxy substrate. The UWB response is obtained by merging the resonances of CRLH unit‐cell and SRR with two additional resonances due to patch feed‐line and ground plane, respectively. Subsequently, the gain of UWB CRLH antenna is enhanced by loading two partial reactive impedance surfaces (PRISs) on the double layer FR4 substrate. First PRIS is embedded directly on the rear side of CRLH antenna (upper layer substrate) whereas the second PRIS is designed on the backside of the lower layer substrate. A considerable improvement in gain is observed over the frequency range from 6.2 to 10.6 GHz with peak enhancement of 1.75 dB. The proposed antenna is fabricated and measured. The measured results indicate −10 dB fractional bandwidth of 126.15% (3‐13.25 GHz) with realized gains of 2.2, 5.25, 5.5, and 7.3 dBi at 3.57, 7.46, 8.92, and 10.59 GHz, respectively. The simulated radiation efficiency is above 61% with a peak value of 86.21%. All measured and simulated results match reasonably well.
Helices are ubiquitous in art and nature. Independent of their pitch and sense of rotation (handedness), helices in sculpture, painting, architecture, scientific illustrations, conference ...announcements, logos, and advertising are eye-catching and aesthetically pleasing. Helices can turn either clockwise (right-handed helix) or anti-clockwise (left-handed helix). The Formula: see text-helix formed by l-amino acids and the double helices formed by Formula: see text-d-2
′
-deoxyribonucleic acid (A- and B-form DNA) and Formula: see text-d-ribonucleic acid (A-form RNA) are all right-handed. Artistic license provides the freedom to create helices of any shape and sense; indeed, many helical sculptures do not follow the natural convention observed in proteins and DNA. What is more surprising, given that models of the Formula: see text-helix and the DNA double helix were published over 70 years ago, is how common left-handed DNA double helices are in the context of scientific papers and books as well as in popular science writing and reporting. In all cases except for left-handed Z-DNA, the use of left-handed helices in scientific illustrations or models is incorrect. Here, we revisit the helix types adopted by peptides, DNA, and RNA, and review examples of right and wrong helical models in science, art, and elsewhere.
The active tuning of surface waves supported by left-handed materials (LHMs) is a major challenge for their practical applications and usability, and graphene has been proposed as an agent for the ...active tuning of surface waves. In this study, tunable surface waves supported by graphene-layered LHM structures are investigated theoretically. The analytical and numerical results are computed for transverse electric (TE) and transverse magnetic (TM)-polarized surface waves. According to the spectral range, two configurations of LHMs (i.e., gigahertz (GHz)-LHM and terahertz (THz)-LHM) are discussed. The physical modeling of graphene is done using the conductivity model based on random phase approximation-based Kubo formalism. The split ring resonator (SRR) model and Kramers–Kronig relations-based causality principle are used for the physical realization of LHMs. To simulate the graphene-layered LHM interface, impedance boundary conditions (IBCs) are applied. Numerical results are computed for dispersion curves, effective wave numbers, and field profiles of surface waves supported by graphene-covered GHz-LHM and THz-LHM. The influence of graphene parameters on the resonance frequency, dispersion curves, and confinement characteristics of surface waves is analyzed for both configurations of LHMs. It is concluded that the graphene-covered GHz-LHM structure supports the tunable surface waves as surface plasmon polaritons (SPPs) support TM-polarized waves. However, with the TE-polarized surface wave, the structure supports the surface polaritons, which do not depend upon the graphene parameters. For the case of the graphene-covered THz-LHM structure, it is concluded that the structure supports the plasmon modes for both polarized waves and the resonance frequency ranges from THz to infrared (IR). The confinement of the TE-polarized surface waves on the graphene layer can be enhanced up to fourfold as compared to the suspended monolayer graphene by using a THz-LHM substrate. Further, the numerical results are found to be consistent with the literature under special conditions. The proposed graphene-layered LHM structure may have potential uses in the active tuning of surface waves, near-field communication and imaging devices, surface waveguide design, and LHM-based metasurfaces.
•Surface waves.•Left-handed material (LHM).•Graphene.•Metamaterial.•Split ring resonator (SRR).
Abstract
Circular dichroism is characterized by distinct optical responses for left-handed and right-handed circularly polarized waves widely used for biological monitoring, analytical chemistry, and ...plasmonic sensing. This work proposes a chiral metasurface composed of a Mushroom-shaped (MS) pattern to achieve circular dichroism in reflection mode at THz frequencies. The maximum achieved absorption efficiency is 98.49% for the left-handed circularly polarized (LCP) incident wave. In comparison, the right-handed circularly polarized (RCP) incident wave is 7.39% at the resonant frequency of 12.4 THz. This high absorption results in remarkable circular dichroism (CD) of 91. 10%. Moreover, a stable response has been observed with the variation of incident angles from 0° to 30°. Meanwhile, power loss distribution, current distribution, and retrieved effective physical parameters have been used in analyzing the absorption mechanism. The high polarization selective absorption efficiency, angular stability, and compact size qualify the proposed design for a diverse range of THz applications.
Left handedness in cardiac surgery—boon or bane? Gohil, Ishan; Sanghavi, Utkarsh; Kothari, Jignesh
Indian journal of thoracic and cardiovascular surgery,
11/2023, Letnik:
39, Številka:
6
Journal Article
Recenzirano
Left-handed individuals consist of around 11% of the population and true ambidextrous consists of only 2–3% of the total population. Almost a similar ratio is seen in medical profession also. ...Difficulties are obvious for left-handed cardiac surgeons in the operating room due to regular right-handed instruments, laterality, and positioning of the patients. In this article, we discuss about the problems and the potential solutions for left-handed cardiac surgeons.
Left‐handedness in otolaryngology, who is right? Alhussien, Ahmed; Alamri, Ahlam; Almjhad, Abdulrahman ...
Laryngoscope investigative otolaryngology,
June 2024, Letnik:
9, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Objectives
This study aimed to ascertain the prevalence of left‐handedness (LH) among otolaryngology—head and neck surgery (ORLHN) practitioners, investigate dexterity's impact on LH trainees, and ...identify common patterns in their training to improve the training experience.
Methods
A web‐based survey was distributed anonymously via email to members of the Saudi Otorhinolaryngology Society. The survey targeted ORLHN attending consultants, board‐certified registrars, and current residents. It consisted of three sections: the first focused on the experience of attending consultants in training LH individuals, the second investigated common maneuvers employed by rhinologists, and the third explored the experiences and impacts reported by LH trainees.
Results
The study included 174 participants, and found a 13.2% LH prevalence among them. Rhinologists showed disparities, with 50% advising trainees to stand on the left side of the bed and use their left hand for the scope, whereas the other half asked otherwise. Additionally, 94.4% of the participants had not encountered any courses specifically tailored for LH trainees. Among LH trainees, 57% and 41% reported difficulties in learning and performing side‐specific procedures such as functional endoscopic sinus surgery and endoscopic septoplasty, respectively, often attempting to switch to their nondominant hand, and feeling disadvantaged due to their laterality.
Conclusions
Left‐handedness presents challenges for both LH trainees and their trainers in surgical specialties, particularly in ORLHN, in which specific positioning and instruments are crucial to gain access to the desired surgical field. Despite these challenges, there is insufficient support for LH individuals. We recommend encouraging LH trainees to openly disclose and discuss their left‐handedness, provide them with mentors, establish standardized operating room setups and techniques, supply appropriate instruments, and demonstrate flexibility in accommodating their needs.
Level of evidence
Level 5.
The purpose of this article is to shed light on the unique challenges faced by left‐handed individuals during otolaryngology—head and neck surgery training residency. It explores the impact of left‐handedness on surgical techniques, instrument availability, learning experiences, anxiety, and future subspeciality choice. By addressing this underrepresented topic, our article aims to provide insights and recommendations to enhance the training experience and inclusivity for left‐handed otolaryngology residents.
Electromagnetic metamaterials are man-made structures that have novel properties such as a negative refraction index, not attainable in naturally occurring materials. Although negative index ...materials (NIMs) in microwave frequencies were demonstrated in 2001, it is still challenging to design NIMs for optical frequencies especially those with both negative permittivity and negative permeability (known as left-handed metamaterials (LHMs)). Here, by going beyond the traditional concept of the combination of artificial electronic and magnetic meta-atoms to design NIMs, we propose a novel LHM composed of an array of upright split-ring pairs working in the near-infrared region. Our electromagnetic simulations reveal the underlying mechanism that the coupling of the two rings can stimulate simultaneously both the electric and magnetic resonances. The proposed structure has a highest refractive index of −2, a highest figure of merit of 21, good air-matched impedance and 180 nm double negative bandwidth, which excel the performances of many previous proposals. We also numerically demonstrate the negative refraction of this metamaterial in both the single-layer form and wedge-shaped lens.
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